The 2022-2026 Technician License question pool notes that signals propagated through the ionosphere, or "skip" propagation, often fade in and out in strength at the receiving station. Why is this? T3A08: What is a likely cause of irregular fading of signals propagated by the ionosphere? A. Frequency shift due to Faraday rotation B. Interference from thunderstorms C. Intermodulation distortion D. Random combining of signals arriving via different paths With long distance propagation using ionospheric skip received signals will often fade in and out, being stronger and weaker over the course of a few seconds. What’s the cause of this irregular fading? A signal arriving at your station antenna may take more than one path to get from its originating station. Signals taking off at slightly different angles from the transmitting station may encounter different densities of ions in the ionosphere and be bent back to the earth along slightly different paths, but each still arriving at the receiving antenna. Signals may also be reflected from the earth’s irregular surface at different angles, both vertically and laterally, resulting again in significant path differences taken between transmitting station and receiving station. But, how does that cause signal fading? Let’s consider the simplest case of two signal waveforms arriving at a receiving antenna. In the figures 1-4 one signal is indicated in red and the other blue. Signal Combination #1: In the first case, the two signals took slightly different skip paths to the receiving antenna, but they arrive very nearly in phase with one another. That is, the waveforms’ electric fields are aligned, or in step, with the positive voltage halves of the cycles and the negative voltage halves of the cycles reinforcing one another. The electric field voltages are summed by the receiving antenna, so the well-aligned waves produce a combined signal on the antenna that is about twice as strong as either signal alone. This is depicted with the upper purple waveform in which the signal amplitude is shown to be about twice that of the individual waves’ amplitudes. This high amplitude produces a relatively strong signal at the receiving antenna. Signal Combination #2: In the second graphic the waves have again taken different paths to the antenna, but the path lengths worked out so that the two waveforms are almost exactly out of phase with one another. When the red signal has a peak positive voltage the blue signal has a peak negative voltage. When these two signals are summed at the antenna the positive voltages and negative voltages sum to zero volts, canceling one another out! (A very low amplitude signal is depicted as the summation in purple, assuming the alignment of the two is not quite exactly opposed.) Signal Combination #3: Of course, other relative relationships of the received signals are possible between the two extremes of perfect alignment and perfect misalignment. The third scenario depicts the two waves somewhat out of phase, but not perfectly opposed. Again, the electric field voltages depicted as amplitude will sum for each position on the waveforms, in this case producing an intermediate amplitude summation signal. You can imagine that there are an infinite number of combination possibilities resulting in variable signal strengths when summed as the receiving antenna’s induced voltages. Signal Combination #4: Another factor that comes into play is signal polarization, as illustrated in the fourth graphic. Not only will signals travel by different path lengths and have variable phase relationships, but the orientation of the electric field oscillations gets scrambled during skip propagation, too. Signals arriving at the receiving antenna with a polarization identical to the antenna’s polarization will produce relatively strong signals (red waveform) as compared to signals arriving with unaligned polarization (blue waveform). So, consider that a receiving antenna may combine two, three, dozens, or thousands of signals arriving via different path lengths, and the phase relationships of all those different waves will be combined into some signal strength at the antenna. Consider further that the polarization of those signals will all be somewhat different, contributing yet more variability into the antenna’s summation function. And finally, consider that as ionospheric conditions of density and ion cloud location shift over time, and even as items on the earth from which signals may reflect move along the surface (ground vehicles, for instance), both the arrival phase relationships and the polarizations will change and shift from moment to moment! The result at the receiving antenna is a moment-to-moment variation in the summation signal strength that produces an irregular fading of signals. The answer to Technician Class question T3A08, “What is a likely cause of irregular fading of signals propagated by the ionosphere?” is “D. Random combining of signals arriving via different paths.” -- Stu WØSTU

Amateur radio operators communicate around the globe on the HF bands thanks to signals propagating by ionspheric skip. High layers of the atmosphere become densely populated with ions - charged particles that result from solar radiation. HF signals, and sometimes VHF signals, are bent (refracted) back toward the earth by these layers of the ionosphere to allow long-distance, over-the-horizon communications. (Read more basics about ionospheric propagation in the suggested related articles below.) The longest distance typical of a single F-layer ionsopheric skip is about 2500 miles. However, reflection of signals from the earth back into the ionosphere are common, allowing multi-skip propagation and much greater communications distances. Multi-skip signals become very weak, in part due to earthly reflections in which signals get absorbed by the earth and scattered by irregular surface terrain and manmade features. However, under some conditions ionospheric propagation can occur without surface reflections, thereby reducing signal losses and achieving very long distance communications. Signals traveling in multiple refractions within the ionosphere before returning to earth can support long-path propagation in which signals travel around the globe in the opposite direction of the shortest distance over the surface between stations. Under some ionospheric conditions, a station may even be able to receive its own signal from propagation around the world, and other stations may hear a slight echo effect from reception of both the short path and long path signals. How is this possible? What's going on here? The refractive strength of ionospheric layers changes with solar conditions, the time of day, and the signal frequency. The steepness of the angle of an ionospheric skip will change commensurately with these factors. When sunspot numbers are great, the ionosphere becomes very densely populated with electrons and positively charged ions, and it is very effective at bending HF signals steeply back to the surface of earth. However, higher frequencies, such as the 10-meter band's 28 MHz signals, will be refracted at shallower angles than lower frequencies, such as the 20-meter band's 14 MHz signals. The refractive effect reduces as frequency increases. Additionally, on the night side of earth where the ionosphere weakens, signals of any frequency will not be refracted as steeply as on the daylight side of the planet where the ionosphere remains strong. Given a proper balance of ionospheric conditions and emitted frequency, the geometry of ionospheric refraction can resemble that of Figure 2 that presents potential ray traces of an HF signal propagating by chordal hops. The name of this propagation phenomenon comes from a geometric term. A chord is a line within and across an arc of a circle or sphere. Signal ray traces over the night side of the earth refract shallowly to form multiple chords until reaching the daylight side where they are more steeply bent back to the earth to be received by stations. The daylight-side ionosphere maintains a stronger refractive effect with its dense population of ions, while the night-side effect is sufficient only to produce the shallow angles of the chordal hops. From this geometry it is easy to see how long-path propagation can result with chordal hops. Since the signals are traveling great distances without the need to reflect from the earth, signal strength is better preserved. -- Stu WØSTU

The 2023-2027 General License question pool inquires about factors effecting propagation of HF signals: G3A10: What causes HF propagation conditions to vary periodically in a 26- to 28-day cycle? A. Long term oscillations in the upper atmosphere B. Cyclic variation in the Earth’s radiation belts C. Rotation of the Sun’s surface layers around its axis D. The position of the Moon in its orbit As I draft this article, the 11-year solar cycle is ramping up cycle 25, with increasing sunspot numbers that are significantly higher than the official predictions. A few years ago, Spot AR2192 shown in the image here was equivalent in area to 33 planet earths in surface area and could be clearly seen by the naked eye when solar illumination was attenuated by smoke, cloud, or fog. [For the record, Ham Radio School does not promote, advocate, or even slightly recommend staring at the sun under any viewing conditions. Bad idea almost anytime.] So, what’s the big deal with sunspots and ham radio? Although sunspots are magnetic regions of relatively cool temperatures that form the darker “spot” in appearance, they are brimming with ultraviolet radiation. The more sunspot area on the face of the sun, the greater the UV rays reaching earth. More UV rays passing through our atmosphere will produce more ions and make the ionosphere denser. A dense ionosphere does a great job of bending some RF signals back toward earth, improving over-the-horizon propagation and communications around the world. So, in short, greater sunspots usually mean enhanced ham radio fun. When the sun it very active with spots, the higher HF bands such as the 10-meter band will open for long-distance communications and provide tons of fun with very little power required. The density of contacts reported in the DXmaps image below gives you the idea. The image here is of self-reported contacts on the 10-meter band within a 15 minute period. The green lines are 10-meter F2 ionospheric layer skip contacts, and the red lines are shorter 10-meter sporadic-E skip contacts. This provides some insight into the nice propagation that high sunspot activity can provide. But the conditions won’t last forever. Sunspots vary over time and, as this question points out, HF propagation conditions will vary along with the sunspots. Two primary cyclical activities impact the sunspot variations. 11 year sunspot cycle: The sun is a complex and dynamic star, and its magnetic activity that drives sunspot creation varies naturally over an 11 year period. Sunspots will increase during the “solar maximum” and decrease near the “solar minimum.” The sun is currently moving toward a solar maximum expected in mid-2025. Solar Rotation: Like the earth, the sun rotates on its axis. The period of surface layer rotation is about 28 days. As the sun rotates the sunspots will pass across the solar disk slowly and eventually rotate out of earth view. Long-lived and large sunspots will often return to again pass across the earth-facing hemisphere of the sun after having rolled around the back side over a couple of weeks’ time. The answer to General Class question G2B10, “What causes HF propagation conditions to vary periodically in a 26- to 28-day cycle?” is “C. Rotation of the Sun's surface layers around its axis.” -- Stu WØSTU

Manufacturers love to brag about it… Operators tend to love the convenience of it… But very few beginner amateurs have a basic understanding of it! Digital Signal Processing, or DSP. What is it all about? What does it do for my station? Before we consider some of the very cool things that DSP can do in our transceiver, let’s make sure we have a little understanding of the whole “digital” thing. Just what is a digital signal? Keeping it practical and related to ham radio, let’s consider the digitization of an RF waveform… from the git go. An RF signal in an electric circuit is an alternating current (AC) signal. That is, the electrons flow back and forth in the circuit at radio frequencies as the voltage reverses polarization, providing electric potential first in one direction and then reversing to the opposite direction. We refer to the polarized voltages as positive and negative voltage. We depict such signals (and their electromagnetic counterparts that are radiated from our antennas) with sine wave forms like that shown to the left, where the amplitude (height) of the wave from the center propagation axis is the instantaneous voltage of the signal as it pulses back and forth. Imagine we are measuring this signal, perhaps with a nice oscilloscope that will show us this waveform on its screen. To the left side of the screen is a scale by which we can measure the amplitude (signal voltage) at any position on the waveform. The oscilloscope is providing us an image of the continuous analog wave – by definition, a continuous or unbroken measurement of the wave, and particularly of its amplitude. But a continuous measurement is difficult to record or represent beyond that nice flowing waveform image. What if we want to represent the waveform with numbers, and specifically, with a limited set of numbers instead of a huge laundry list of values? We could set our oscilloscope to measure the wave’s amplitude in discrete steps across the waveform, perhaps 10 separate instantaneous measurements per wavelength over equal intervals of time. In the figure below each blue dot represents a point in time of a discrete sample of amplitude. A table of measures is included that indicates how these discrete samples of waveform amplitude can be numerically represented, sampling over time left-to-right across the waveform. If we were to create a waveform strictly from the numerical data in the table it might look something like the oscilloscope image to the right. The amplitude value is updated only with each new discrete measurement, so the waveform takes on a stepwise form – the information between the measurements is lost, but much of the information contained in the waveform is still recoverable, such as amplitudes, frequency, and wavelength information. If we take a lot more samples in the same amount of time, measuring more frequently, we will record a more accurate depiction of the waveform more closely resembling its true smooth form. That will require recording lots more numbers. If we sample too sparsely we reach a threshold at which the numerical information is insufficient to accurately depict the waveform. Recording discrete measurements like this over time is one form of analog to digital conversion (ADC). The digital signal is simply a list of numbers like in the table above. We can assault the list of numbers with a wide variety of mathematical weapons in our DSP arsenal, forcing the digital waveform to comply with our whims. Of course, in the Digital Signal Processing of a receiver the digital representations are created by sampling with very fast and efficient electronic circuits in lieu of a clunky oscilloscope. The processor itself is much like the microprocessor in a modern personal computer, only optimized for rapid processing of the signal numerical data. Further, after the mathematical processing of the digital signals, the DSP must perform a digital to analog conversion (DAC) so that re-smoothed waveforms are provided to later demodulation stages and ultimately to the receiver’s audio circuits for sound reproduction. By the application of filters, averaging circuits, and other techniques the stepwise digital signal representations are smoothed back into analog signals. So, a typical Digital Signal Processing system will perform an analog to digital conversion on received signals, operate mathematically on the digital representations, and then perform a digital to analog conversion for modified RF signal output, like this: If you have studied the signal processing stream of a heterodyne receiver, as in Section 6.2,Receiving, of the HamRadioSchool.com Technician License Course, you’ll recall the block diagram of the receiver’s components and the signal processing accomplished by each stage. And I know you have the burning question in your head, “Just where does this DSP stuff happen in the receiver processing stream?” The Digital Signal Processing may be applied in a couple of different places and with multiple purposes. Some modern receivers with very fast-sampling electronics will digitize the RF signal immediately -- that is, the digital representation is of the RF signal itself before any analog processing occurs. Often, these receivers are in what is termed a software defined radio (SDR). The RF signal is processed as digital information throughout the demodulation stream, including the processes described below, and finally converted to analog audio signals for sound output. Other receivers of perhaps slightly older vintage may employ DSP following the intermediate filter (IF) stage. Remember, the IF results from the analog mixing process between RF signals and a variable frequency oscillator, shifting the modulated signal to a much lower frequency on the demodulation path to audio. (See our Heterodyne Receiver article.) The IF is sampled and operated upon in near-real time by the DSP to do any of the following: Filter out undesirable mixing products from the receiver’s IF passband Filter out noise using any of several digital noise reduction algorithms Identify any potential offending strong carrier signals and notch filter it (or them) out of the passband Change the width of the IF passband filter to fit the bandwidth of the operating mode (SSB, CW, AM, or digital mode variations) Provide custom filter shapes and effects as defined by the operator …and other possible signal processing, depending upon the manufacturers inclusions. Digital Signal Processing may also be applied in the audio processing stage following the product detector (labeled “Mixer 1” in figure below). While many of the same types of filters and effects can be implemented at this stage as at the IF stage, it is usually more effective to perform those functions at the IF filter stage and avoid passing undesired signals further along the receiver processing path. However, DSP can be readily applied to perform audio functions such as equalizing received audio, audio filtering, audio mixing, and speech processing such as compression or expansion. DSP can be used to provide some of these audio processing features in a transmitter as well, particularly to perform speech processing to enhance your transmitted signal’s intelligibility. The algorithms used in DSP are complex and will not be described in detail in this article. However, let’s consider one light and somewhat simplified view of a commonly implemented technique that will help provide an intuitive understanding of how DSP’s innards work. Imagine we have a sample of a very complex RF waveform. By applying a mathematical transform known as the Fourier Transform, the waveform’s time-based representation can be converted into a frequency representation. That is, the DSP can compute all the different sine wave component frequencies comprising the complex signal form, as well as the amplitude of each frequency. (See sidenote below.) A Fourier Transform Note: Any waveform can be created by a combination of multiple sine wave components of different frequencies and amplitudes. So, any RF signal can be “decomposed” into a larger set of nice sine wave signals. The Fourier Transform shows us the set of frequencies and the amplitude of each that sum together to create a more complex or irregularly shaped signal. With the digital signal data organized into a frequency spectrum representation, the frequencies may be filtered in many different ways. For example, all frequencies above a desired cutoff value can be digitally eliminated (amplitude value set to zero), and all frequencies below a different cutoff value can be similarly eliminated, thereby leaving only a narrowed desired band of frequencies, as depicted below. The high and low cutoff frequencies define the filter width, or passband. This narrower band may be DA converted back into analog form for further receiver processing, leaving the undesired signals behind. Imagine that a very narrow spike frequency amplitude exists in this spectrum – a tiny range of frequencies with amplitude much greater than the surrounding frequencies – indicating the presence of an undesired carrier frequency in this band. This scenario is depicted below. The Digital Signal Processing can identify the unusually strong carrier signal by its high amplitude numerical values and use logic to create a filter that sets the amplitude of just that narrow band of unusually strong frequencies to zero. Poof! It’s gone in a puff of digital logic! This is a notch filter, ridding the desired passband of the annoying strong carrier signal. Many other techniques are used in Digital Signal Processing algorithms to implement noise reduction and other functions. DSP can help you bring in those really weak signals from distant stations that you may otherwise miss altogether! If your SSB receiver has DSP features, or if you have a capable software defined radio, read your user’s manual and become familiar with the basic controls and capabilities for using DSP. Now that you have a basic introduction to Digital Signal Processing, you should be able to interpret most of the functions and descriptions. Good luck, and 73! -- Stu WØSTU

The 2020-2024 Extra License question pool asks you to identify characteristics of a spectrum analyzer, a common RF engineering signal measurement device: E4A02: Which of the following parameters does a spectrum analyzer display on the vertical and horizontal axes? A. RF amplitude and time B. RF amplitude and frequency C. SWR and frequency D. SWR and time Let’s first frame this question about a measurement device with a general description of the types of signals that hams commonly wish to measure, and the correct response will precipitate right out of the signal description. In the General License Course we introduce a 3D model of waveform signals from which either a time domain view or a frequency domain view may be considered. This 3D model is reprised in the Extra License Course book, and we'll use it again here in examining Extra question E4A02. (For an examination of time and domain views of signals, see this Ham Radio School article: Time & Frequency Domain Views.) The 3D model depicts a complex signal comprised of a few thousand hertz of bandwidth. In this particular depiction the model is depicting an audio band from approximately 200 Hz to 3000 Hz, typical of an audio band that might modulate a SSB RF signal. For viewing clarity, only a sampling of a few specific frequency waveforms are shown across this bandwidth, else the image would be too cluttered with 3000+ waveform images. Further, you can imagine a similar complex RF signal by bumping up the frequency values by several megahertz. In the model, waveforms are imagined to be moving across the axis that indicates their frequencies, and each waveform of different frequency varies in amplitude as it flows along, commensurate with the variations of power in each frequency. For this audio signal, perhaps encoding an operator’s voice, the lower frequencies that are typical of vowel sounds are usually of greater amplitude than the higher frequencies more commonly produced by consonant sounds. If our model was dynamic instead of statically welded in an image on this page, we would observe the waveforms flowing happily along, each one growing and shrinking in height as the characteristics of the voice’s sound ebbed and flowed and enunciated a variety of words. An oscilloscope is a measurement device that displays the time domain view of a signal. When an AC signal is fed into the input of the oscilloscope, the scope measures the voltage of the signal over a brief time period that is usually selected by the scope operator. The oscilloscope plots the measured voltage of the signal on the vertical axis of the display, thereby depicting the amplitude of the input signal over time that is plotted on the horizontal axis. The image is from the perspective of our model viewer on the left, a sine wave varying over time -- the time domain view. The model viewer on the right, however, is getting a much different picture. He has a view across the range of frequencies contained in the signal, seeing each frequency as a vertically plotted bar. He observes the changing amplitude of each different frequency as the changing height of each frequency’s bar over time. However, he has no “time axis” to view. While the amplitudes of the frequencies are depicted on the vertical axis similar to the oscilloscope plot, the horizontal axis is now depicting frequency, or the signal spectrum. This view is very similar to that observed on many audio frequency equalizer displays, on which the amplitudes of frequencies dance up and down with the voice or music signal routed through the equalizer. This is the frequency domain view. The view of our friend on the right is that depicted by a measurement device called a spectrum analyzer, and these devices display a range of frequencies across the horizontal axis and amplitude on the vertical axis. The answer to Extra Class question E4A02, "Which of the following parameters does a spectrum analyzer display on the vertical and horizontal axes?" is “B. RF amplitude and frequency.” -- Stu WØSTU

Operational amplifiers (commonly called op amps) are a ubiquitous building block for designing electronic circuits. Today, these devices are fabricated as small integrated circuits but the concept started long ago using vacuum tubes. Op amps are commonly used for DC and audio circuits but high-performance op amps can be used at radio frequencies. Ideal Operational Amplifier To understand basic op amp functions, we use the concept of the Ideal Op Amp. The Ideal Op Amp is a voltage-controlled voltage source as shown in Figure 1, with these attributes: 1. Infinite gain (Av) and infinite bandwidth 2. Zero output impedance 3. Infinite input impedance (zero input current) An important fourth attribute is usually included but it is only valid if there is negative feedback applied to the op amp: 4. Zero volts between the two inputs These ideal op amp assumptions are quite amazing: infinite bandwidth and infinite gain? A key point is that for typical low frequency circuits, these assumptions hold quite well due to the excellent performance of common op amps. For more demanding applications, we may need to do a more careful analysis to understand how the circuit will perform. But for our purposes, we will just use the ideal assumptions. The cool thing about op amps is that for many non-critical applications the op amp performance (gain, bandwidth, impedance, etc.) is so good compared to the circuit requirements that they really do act like ideal op amps. They are easy to design with and have become an essential building block for electronic systems. In case you are wondering how this op amp gets its power, there are two power supply connections (positive and negative) for the device, often neglected when discussing the circuit design (but are absolutely essential when wiring up a real circuit). Typically, bipolar power is supplied, + 15 and - 15 volts, which supports a healthy signal swing. Non-Inverting Amplifier The first common op amp configuration we will look at is the Non-Inverting Amplifier. (I always wonder why we don’t call this the “regular amplifier” configuration or maybe just “amplifier.”) In this configuration, we see that we have feedback from the output back to the inverting input. This means that the two inputs will always have zero voltage across them. Because no current can flow into the inputs, the voltage present at the non-inverting input is determined by the voltage divider formed by R1 and R2. Rearranging to obtain the gain of the amplifier, Notice that the voltage gain of the circuit does not depend on the gain of the op amp. We are assuming that if the op amp gain is really big, then enough feedback will be applied to the non-inverting input to produce the desired function. Let us check that assumption about the two op amp inputs having zero voltage between them. Suppose the non-inverting input is a few millivolts higher than the inverting input. The huge voltage gain of the op amp would cause the output to increase, which would feedback via the resistor divider to the inverting input. An increased voltage on the inverting input will cause the op amp output to decrease until both inputs have the same voltage. Thus, the high gain of the op amp plus negative feedback keeps the input voltages the same. Buffer Amplifier A special case of the non-inverting amplifier is the buffer amplifier (also called unity-gain amplifier or voltage follower), having a voltage gain of one. This is equivalent to making R2 zero and R1 infinite in the non-inverting amplifier configuration. Again, negative feedback is applied such that the voltage between the op amp inputs is zero. This makes for a good buffer amplifier, with infinite impedance on the input and zero impedance on the output. Ideally, at least. Inverting Amplifier Another common op amp circuit is the inverting amplifier as shown in Figure 4. As the name implies, the output voltage is amplified with opposite polarity as the input. This circuit is analyzed by noting that both inputs of the op amp will be at zero volts. The non-inverting input is connected to ground and the inverting input will be driven to the same voltage via feedback through the resistors. We also note that current i flows through both resistors because no current enters the inverting input of the op amp. Rearranging to obtain the gain of the amplifier, The minus sign in the gain is important and must be considered in applying the circuit. In some situations, it may not matter, you just may need to amplify the input signal without regard to changes in polarity. In other cases, the polarity may be critical and your signal could end up being “upside down.” We assumed that we have ideal op amps but we didn’t say anything about the resistors. The gain of these circuits will depend on the actual values of the resistors and therefore their tolerance. Summary These common op amp circuits are useful for amplifying various analog signals. The ideal op amp model helps us understand how these circuits operate. For more detailed information on op amp circuits, refer to the excellent material in References 1 and 2. References 1. Handbook of Operational Amplifier Applications, Bruce Carter and Thomas R. Brown, Texas Instruments, Sept 2016, http://www.ti.com/lit/an/sboa092b/sboa092b.pdf 2. Op Amps for Everyone, Ron Mancini, editor, August 2002, https://web.mit.edu/6.101/www/reference/op_amps_everyone.pdf

The 2023-2027 General License question pool asks about the inner workings of vacuum tubes used as amplifiers: G6A10: Which element of a triode vacuum tube is used to regulate the flow of electrons between cathode and plate? A. Control grid B. Heater C. Screen grid D. Trigger electrode Vacuum tube amplifiers are widely used in amateur radio to boost RF signal transmission power. The basic operation of a vacuum tube is much like a field effect transistor (FET), with a transmitter signal voltage controlling a large current to boost the power of transmission to the antenna. Triode: A triode vacuum tube has three primary elements: Cathode, Plate, and Control Grid. A heater, or filament, is energized near the negative potential cathode to cause electrons to be released. The positive potential plate, or anode, attracts the released electrons, so a current flows from cathode to plate. This current can become quite large for high power operations. A control grid is positioned between the cathode and plate. This grid is essentially a screen of fine filaments or wires connected to a controlling voltage from the transmitter. By varying the voltage on the intervening control grid the current flowing from cathode to plate may be commensurately varied. When the voltage of the control grid is positive it will help to accelerate electrons from the cathode. The vast majority of these will accelerate rapidly toward the control grid and pass right through its gaps and on to the positive potential plate. When the control grid voltage is negative it will repel the cathode’s electrons, reducing or terminating the current flow to the plate. As the voltage of the signal to the control grid varies across a range of values associated with the signal of transmission the current through the vacuum tube mimics this signal and provides amplification for a powerful transmission. Tetrode: A related question pool item (G6A12) involves a four-element vacuum tube called the tetrode. The tetrode is nearly identical to the triode except for the addition of another grid called the screen grid. The screen grid is positioned between the control grid and plate, usually closer to the control grid than to the plate. Normally the screen grid is connected to a positive DC voltage slightly less than that of the plate. The screen grid’s purpose is to reduce capacitance that arises between the control grid and the plate. Such parasitic capacitance can cause the tube’s circuit to become self-resonant at some frequencies, and it will reduce the tube’s achievable gain at higher frequencies. This problem is called the Miller Effect, and the screen grid helps to resolve it. A triode amplifier will typically require some type of “neutralization” circuit outside of the vacuum tube to avoid the detriments of the Miller Effect. Configuration: Although these graphics depict the cathode, grids, and plate in a flat configuration within the vacuum tube enclosure, the more common configuration is a concentric circular or oval arrangement for these elements. The heater and cathode are the inner-most elements, surrounded by the grids, and the plate encircling the outer perimeter. Electrons flow from the inner cathode out to the surrounding plate through the grids. The answer to General License question G6A10, “Which element of a triode vacuum tube is used to regulate the flow of electrons between cathode and plate?” is “A. Control Grid.” -- Stu WØSTU

It seems that when people are studying for their ham radio Technician license exam, they understandably get very focused on learning the material and passing the FCC exam. Suddenly, the Volunteer Examiner tells them “you passed” and the thrill of success bursts forth! This is sometimes followed by the question: I got my license, now what? The most general answer to this question is “find something you are interested in doing and do it.” For many new hams, this is easy— they just need to think about what got them interested in ham radio and follow that path. But other folks have this basic idea that they “want to do ham radio” but may not be sure how to actually get started. This article is to give you some ideas on what to do, assuming you have a Tech license and some basic 2m or 70 cm radio equipment. If you haven’t already connected up with some local radio hams, give that a try. Having someone to talk to about various ham radio activities can really help. If you have a radio club in the area, be sure to connect up with them and attend a meeting. (See the ARRL listing of ham radio clubs.) Here are some ideas for radio activity to help get you started (in no particular order): Public Service Often people get interested in amateur radio to provide a service to the community. There are many opportunities to get involved in helping out with events such as walkathons, marathons, bike races, etc. Communications support may be provided by a ham radio club or, more likely, the local Amateur Radio Emergency Service (ARES) group. The Radio Amateur Civil Emergency Service (RACES) is another public service organization, normally associated with a governmental agency such as the county sheriffs department. Sometimes ARES and RACES are combined into one group. The ARRL has a web page that compares the two organizations. Most ARES and RACES groups have some kind of “registration database” for you to sign up. However, it usually works best to reach out and find the local hams that are in charge of these groups and let them know you are interested. Find out when they hold their meetings and on-the-air nets and join in. Make yourself visible and available. Emergency Communications Often I hear new hams say they are interested in emergency communications or as the ARRL says When All Else Fails. They’ve heard about or experienced landline and mobile phones getting overloaded during blizzards, hurricanes and wildfires and want to have alternative communications. The prepper community refers to this as SHTF. Being prepared for emergencies boils down to two basic questions: 1) what are the conditions that you are preparing for? 2) who do you want to communicate with? Most likely, you need to be ready for a power outage of some duration, which implies the use of battery backup or a gasoline generator to power your radio equipment. Who you want to communicate with varies from just your immediate family over short distances to being able to contact other hams much further away. Thinking through the answers to these two questions will get you started on creating the desired communication capability. Find A VHF/UHF Repeater Another way to connect with the local amateur radio community is via VHF/UHF repeaters. These things are the utility mode for communicating locally. Take a look at How to Choose a Repeater for some tips on finding a repeater that works for you. Introduction to VHF/UHF Repeaters provides an excellent overview of how repeaters work. Develop Your Home Station Many hams start out with a VHF/UHF handheld transceiver (HT), which gets them on the air quickly. This really is a ham shack in your hand, which is useful for many activities. By itself, the HT has limited range, so many hams are interested in extending its range. One thing you can do is attached an external antenna to the HT to give it greater radio coverage (see Considering a VHF/UHF Antenna for Your Home?). This will increase your simplex range and allow you to hit more distant repeaters. Another thing to consider is establishing a VHF/UHF home base station (see A VHF FM Station at Home), which provides more output power to increase coverage. Single Sideband on VHF While the majority of VHF operating is using FM, there is a whole ‘nuther world out there in the weak-signal operating modes. We call this “weak signal” since we are often pulling signals out of the noise to make a contact. Signal Sideband (SSB) is the preferred voice mode when signals are weak since FM performs poorly when the signal level drops. You’ll also find quite a bit of Morse Code CW (Continuous Wave) communication used since it is even better than SSB when the signals are weak. To play with SSB, you need an all-mode transceiver that operates on VHF such as the Yaesu FT-857D or FT-817ND. You’ll also need to get a suitable antenna, one that is horizontally polarized and probably a yagi antenna with gain. See these related articles: SSB on 2-meters: The other VHF mode Getting Started on 2-Meter SSB Single Sideband Advantages The 6m band is known as The Magic Band because it can suddenly come alive with signals bouncing off sporadic-e clouds in the ionosphere. On most days, 6 meters acts like any other VHF band with mostly local propagation. But when the sporadic-e hits (very common in the summer months), you can talk across North America. When the normal sunspot cycle is strong, we can also get F2 propagation, which allows contacts to be made into Europe, South America and Asia. Learn more about VHF over-the-horizon propagation with this article: 10m, 6m, 2m Over-the-Horizon Propagation Space Contacts Another great use of the 2m and 70 cm bands is to contact outer space. The International Space Station (ISS) has a ham radio station on board and most of the astronauts have their amateur radio license (see ARISS). The primary use of this station is for contacts with schools as part of NASA education outreach mission. However, the astronauts sometimes decide to make contacts on their own time. It really depends on the interests of the astronaut and a few of them have really gotten into making random ham radio contacts. Also, very often there is a packet radio station transmitting from the ISS such that you can “digipeat” through the station to contact other hams on earth. It is even a fun exercise to see if you can successfully track the ISS and then hear the packet station transmitting. The ISS is in low earth orbit (LEO), so it is usually overhead for only 10 minutes or so, depending on the pass. Another type of space operation is using OSCAR (Orbiting Satellite Carrying Amateur Radio) satellites, which are basically repeaters in the sky. These satellites are also in LEO so you repeat through them to contact other hams while you both have the satellite within range. Some of these satellites use FM, so you can work through them using just a dualband (2m/70cm) HT and a small yagi antenna. It does take a bit of study and practice to track the satellites, figure out the right frequency, point the antenna and adjust for doppler shift. But that is what makes it a fun learning experience and radio challenge. See the AMSAT web site for more information, and check out this Ham Radio School article: Amateur Satellite Contacts. For a summary video on satellite ops, see WØSTU's "Satellite Operations" video in Chapter 11 Space Contacts of the Technician Learning media page. Summits On The Air The Summits On The Air (SOTA) program is a great combination of hiking and portable ham radio operating. The basic idea of SOTA is to operate from a designated list of summits or to work other radio operators when they activate the summits. The designated summits are assigned scoring points based on elevation with scoring systems for both activators (radio operators on a summit) and chasers (radio operators working someone on a summit). A basic VHF SOTA station is a handheld FM transceiver with a ½-wave telescoping antenna. The standard rubber duck on a handheld transceiver (HT) is generally a poor radiator so using a ½-wave antenna is a huge improvement. Just stuff the HT and antenna in a backpack along with the usual hiking essentials and head for the summit. See How To Do a VHF SOTA Activation. Packet Radio and APRS Some new hams are interested in digital communications via amateur radio. This is a great way to blend computer technology and radio communications. There are many ways to do this but packet radio is one of the most common on the VHF/UHF bands. Simply put, packet radio uses relatively slow speed modem tones (1200 or 9600 baud) fed into an FM transceiver using a Terminal Node Controller (TNC). The transmissions are in “packet form” using the AX.25 protocol, which is handled by the TNC. Think of it as “SMS text messaging before there was text messaging.” One of the most common usages of AX.25 packet is the Automatic Packet Reporting System (APRS). APRS is quite versatile but the most common use is position reporting, with a robust set of internet-based mapping tools to plot the position of a particular ham radio stations. For example, the figure to the right shows the track of Steve WG0AT as he ascended a SOTA mountaintop in Colorado. Work the High Frequency Bands I’ve mostly given examples of VHF/UHF operating, but a Technician license does give you some useful operating privileges on the High Frequency (HF) bands. In particular, Techs have voice privileges on 10 meters (28.3 to 28.5 MHz). When the sunspots are active, 10m is an awesome worldwide DX band. You literally can talk around the world. To do this, you’ll need a transceiver capable of SSB on the 10m band and a suitable antenna. The antenna does not have to be exotic — a simple dipole or 1/4-wave vertical can do well. If you get hooked on the fun of HF DX, then you’ll want to start working on your General Class License. But that is a topic for another day. -- Bob KØNR

Most new hams get started on the ham bands using FM, with 2m and 70cm being the most popular bands. This is a great way to get started using VHF simplex and repeater communications. FM is the most popular mode primarily due to the wide availability of FM repeaters. These repeaters extend the operating range on VHF and enable low power handheld transceivers to communicate over 100 miles. FM is also used on simplex to make contacts directly without repeaters. The main disadvantage of FM is relatively poor performance when signals are weak, which is where SSB really shines. A weak FM signal can disappear completely into the noise while a comparable SSB signal is still quite readable. How big of a difference does this really make? Perhaps 10 dB or more, which corresponds to one or two S-units. Put a different way, using SSB instead of FM can be equivalent to having a beam antenna with 10 dB of gain, just by changing modulation types. So this is a big deal and radio amateurs interested in serious VHF work have naturally chosen SSB as the preferred voice mode. (You will also hear them using Morse code or CW transmissions, which is even more efficient that SSB.) As an example of what is possible on SSB, during one VHF contest I was operating portable in Colorado Springs. I had just dismantled my 2m yagi antenna and was listening to 2M SSB on a short mobile whip antenna. Suddenly, I heard WA7KYM in Cheyenne, Wyoming calling CQ from about 160 miles away. I figured that with my puny little antenna and only 10 watts of power, there was no way he was going to hear me. But, what they heck, it was a contest and it would be more points so I gave him a call. To my surprise, WA7KYM heard me and we made the contact without much signal strength to spare. Now, to be accurate, this contact has more to do with WA7KYM’s “big gun” station (linear amplifier, low noise preamp and large antenna array) than it had to do with my 10 watts and a small whip. The key point here is that this contact would not have happened using FM and was only possible because of SSB. When and Where to Operate The SSB portion of the 2m band runs from 144.100 MHz to 144.275 MHz and Upper Sideband (USB) is used. The 2M SSB calling frequency is 144.200 MHz, so that is the first place to look for activity or to call CQ. SSB operation is not channelized like FM simplex and repeater operations, so you’ll need to tune around to find other stations on the band. A station may be operating anywhere in the SSB sub band, and not one any specifically designated frequency or channel. As a result, and as compared with FM, adjusting the transceiver frequency is much more critical. If you are not precisely aligned on the same frequency as the station you are listening to, the audio will sound odd. Fine tuning adjustments will be needed to get the audio tone of the received station just right. One of the realities of 2M SSB operation is that many times, no one is on the air. There is just not that much activity out there, as compared to 2m FM. Some amateurs get discouraged, turn off the radio and and miss the thrill of working distant stations during a band opening. To get started on 2m SSB, the trick is to get on the air at times when you know there will be activity— during VHF nets and VHF contests. VHF Nets You will need to check around to see if there is a SSB VHF Net in your area. Find out what time it is held and the frequency of operation. Checking into the net is a great way to try out SSB and to make contact with the 2m SSB operators in your area. VHF Contests Think of VHF contests as “VHF activity weekend” since they are a great opportunity to just get on the air and work 2M SSB enthusiasts. The main contests are the ARRL June VHF Contest, the ARRL January VHF Sweepstakes, the ARRL September VHF Contest and the CQ Worldwide VHF Contest in July. For more information, take a look at this article from my personal ham radio blog: How to Work a VHF Contest. Equipment The required equipment for getting started on 2M SSB is pretty basic – a transceiver capable of 2M SSB and a 2M antenna. The 2M antenna you already have is probably vertically polarized since that is what we use for 2M FM, both mobile and base stations. All of the 1/4-wave and 5/8-wave antennas that are commonly used for 2M mobile work are vertically polarized. Most omni-directional base station antennas such as those made by Cushcraft, Diamond, Comet, etc. are vertical, too. These antennas will work for SSB but most of the really active 2m SSB stations use horizontally-polarized antennas. Vertically-polarized stations can work horizontally-polarized stations but there will be a substantial signal loss (about 20dB). If vertical is all you have, then give it a try. If you can get a horizontal antenna, then your results will be much better. The most common horizontally-polarized antenna on 2m is a Yagi mounted so that its elements are parallel to the ground. There are a variety of horizontally-polarized, omni-directional mobile antennas, such as the HO antenna made by M2 (see http://www.m2inc.com). Get on the Air This information is intended to get you started on your way to operating 2m on the SSB portion of the band. You will learn more as you get into it and you will find that most of the people hanging out down on sideband are friendly, knowledgeable and helpful. They are always happy to see a new operator on 2m sideband. -- Bob K0NR

You’ve just purchased your first handheld transceiver and have been chatting with both old and new friends around town on the 2 Meter band. There are many different frequencies to choose from, so how do you find an appropriate frequency to use? FCC Rules The first thing we need to know are the frequencies that the FCC has authorized for our particular license class. For the HF bands, the frequency privileges depend greatly on the license class of the operator. Above 50 MHz, the frequency allocations are the same for Technician licenses and higher. In particular, the 2m band extends from 144 MHz to 148 MHz. The FCC Rules say that any mode (FM, AM, SSB, CW, etc.) can be used on the band from 144.100 to 148.000 MHz. The FCC has restricted 144.0 to 144.100 MHz to CW operation only. Band Plans Knowing the FCC frequency authorizations is a good start but we need to check a bit further. Amateur radio operators use a variety of modulation techniques to carry out communications. Often, these modulation techniques are incompatible since a signal of one type can’t be received by a radio set to another modulation type. For example, an SSB signal can’t be received on an FM receiver (and vice versa). We need to use our authorized frequencies wisely by sharing the band with other users and avoiding unnecessary interference. Thus, it makes sense to have a band plan that divides the band up into segments for each type of operation. 2 Meter Band Plan As shown in the table, the ARRL 2 Meter amateur band plan supports a wide variety of radio operation. Large portions of the band are dedicated to FM operation, consistent with the popularity of the FM mode. There are portions of the band designated for repeater outputs (which is the frequency that we tune to receive the repeater) and repeater inputs (which is the frequency we transmit on to use the repeater). Notice that these segments are positioned 600 kHz apart consistent with the standard 2m repeater offset. There are also frequencies designated for FM simplex. On the low end of the band, we see segments for some of the more exotic modes. At the very bottom is the CW portion, which includes Earth-Moon-Earth (EME) operation. EME operators communicate by bouncing their signals off the moon. 2 Meter Band Plan Adapted from the ARRL web site Further up the band, we see segments for SSB operation and beacon operation. SSB is the preferred voice mode for so-called “weak signal” operators. The mode is more efficient than FM when signals are weak, so it is the way to go when you are trying to push the limits of 2m DX. Beacons are transmitters that are always on, transmitting a short CW message as a propagation indicator for distant stations. We often think of 2 Meters as a local coverage band but when conditions are right, contacts can be made with stations over a thousand miles away. Of course, conditions are not always right so having a beacon on the other end of the desired communication path lets you know how propagation is in that direction. Radio amateurs also use 2 meters for OSCAR (Orbiting Satellite Carrying Amateur Radio) operation, sending signals to a satellite (uplink) or receiving signals from the satellite (downlink). The OSCAR segments don’t specify a particular modulation type since CW, SSB and FM are all used for OSCAR operation. Because of their elevation above the earth, satellites can hear signals from all over the US simultaneously, so they are very susceptible to interference. Most of this non-FM operation can be easily interfered with by signals from other users. EME signals, for example, are usually quite small since the signal has to make the round trip from the earth to the moon and back. If a local FM operator fires up in the EME portion of the band, an EME signal that can’t be heard by an FM receiver can be wiped out by the FM signal. Similarly, an operator chatting across town on 2m could interfere with a satellite hundreds of miles away and not know it. This is particularly a problem with FM receivers, which won’t even notice low-level CW and SSB signals. FM Operating The most common VHF radios are basic FM mobile or handheld transceivers. These radios usually tune the entire 2m band from 144 MHz to 148 MHz in 5 kHz steps. The band plan indicates the proper range of frequencies for FM operation but there is more to the story. FM operation is “channelized”, meaning that specific 2m FM frequencies are identified by the band plan. The use of channels is especially important for repeaters since they don’t easily move around in frequency and are coordinated to minimize interference. The idea is to have all stations use frequencies that are spaced just far enough apart to accommodate the signal without interfering with the adjacent channels. You might think that the spacing between channels would be 5 kHz, which is the tuning step of most FM radios. This doesn’t work because a typical FM signal occupies a bandwidth that is about 16 kHz wide. The channel spacing needs to be at least as wide as the bandwidth of the signal, which allows room for each signal without interfering with the adjacent channel. In Colorado, the channel spacing is 15 kHz, which is a bit tight for our 16 kHz-wide signal. In other parts of the country, a 20-kHz spacing has been adopted to provide for more separation between channels. Obviously, you get more channels on the band with 15 kHz spacing than with 20 kHz, but you have to put up with more adjacent channel interference. When using a repeater, you just need to dial in the published repeater frequency and set the transmit offset, usually either + 600 kHz or – 600 kHz for a 2-meter band repeater. In some parts of North America, non-standard repeater offsets may be used, which will be indicated in the repeater directory. For repeaters that require a CTCSS tone for repeater access, you will have to set the proper tone frequency on transmit. Choosing an appropriate simplex frequency can be a little tricky, since it depends on whether your region uses the 15-kHz or 20-kHz channel spacing. Across all of North America, the National Simplex Frequency (also referred to as the calling frequency) is 146.52 MHz. In areas that use 15-kHz channels, the adjacent channels are 146.535, 146.550, 146.565 MHz, etc. moving upward. Below the calling frequency are 146.505, 146.490, 146.475 MHz and on. In areas that use 20 kHz channels, the frequencies are 146.540, 146.560, 146.580 MHz moving up and 146.500, 146.480, 146.460 MHz moving down. There is usually another group of FM simplex frequencies in the 147 MHz. The typical layout of simplex channels is the table below. However, it is important to note that your local band plan may be different than this. 2m FM Simplex Frequencies (typical usage, check your local band plan) 15 kHz Channels 146.400, 146.415, 146.430, 146.445, 146.460, 146.475, 146.490, 146.505, 146.520, 146.535, 146.550, 146.565, 146.580, 146.595, 147.405, 147.420, 147.435, 147.450, 147.465, 147.480, 147.495, 147.510, 147.525, 147.540, 147.555, 147.570, 147.585 20 kHz Channels 146.400, 146.420, 146.440, 146.460, 146.480, 146.500, 146.520, 146.540, 146.560, 146.580, 146.600, 147.400, 147.420, 147.440, 147.460, 147.480, 147.500, 147.520, 147.540, 147.560, 147.580 Band Plan While the ARRL band plan sets the guidelines for band use across the US, VHF band plans are really defined on a statewide or regional basis. This means it is best to find the specific band plan for your region. This may be a challenge to find the right information, but try searching the web for “2-meter band plan” and your state. A good source is your local frequency coordination body. Inquire with a local club or experienced ham about your local coordinating body, or conduct an online search for your area. Summary The fine points of the band plan can be a bit confusing. However, a few simple guidelines can help, especially if you are operating only FM. FM voice simplex and repeater operation should only occur in the designated band segments for your area. Stay out of the weak signal and satellite sub-bands. When operating through a repeater, make sure you are tuned to the published repeater frequency with the proper transmit offset. When operating simplex, use a simplex frequency designated by your local band plan. We’ve only covered the 2 Meter band in this article. If you are operating on other bands, be sure to check the appropriate band plan before transmitting. You can read about the 70 centimeter band plan in a counterpart article, What Frequency Do I Use on 70 Centimeters? Bob, KØNR

Are you ready to establish a home station for FM ops on the VHF and UHF bands, and are you wondering what you need to do about an antenna? Let’s review some of the things you need to consider in establishing a highly performing antenna for your home station, including antenna types, coaxial cable characteristics, connectors, and more! During a previous devastating wildfire in our area of central Colorado, my good friend and colleague, Randy, had great difficulty maintaining solid radio communications through our local repeater from his home. His signal just wasn’t quite strong enough to be readable. Our local hams kept the repeater very busy during the days of the fire relaying the latest information gleaned from emergency response links, commercial sources, ARES and RACES volunteers, and more. It was a valuable resource in our community for rapidly disseminating fire information. Randy has been using a 2-m/70-cm dual band HT with one of those really convenient, crappy antennas we refer to as a rubber duck. His home is located just on the leeward side of a hill from the repeater that is about 7.5 miles distant. The 5 watts of his HT coupled with the rubber duck antenna just didn’t quite provide the performance he needed to reliably hit the repeater with a readable signal. After the fire emergency, Randy decided it was time to upgrade his station for more reliable operations in the local area. While he plans a future station upgrade to a more powerful mobile-base transceiver, he sought first to improve his home antenna such that he can use the HT in the short term and integrate a mobile-base transceiver later. I had a terrific time helping Randy review some of the factors involved in erecting a VHF/UHF dual band antenna for 2m and 70cm bands and then helping him install and test it out. Let’s take a look at some of the things Randy and I considered for his antenna project and wrap up with a description of his solution. Some Antenna Considerations In one brief article we can’t cover every detail that you might want to think about in selecting a VHF/UHF antenna for your home or shack, but let’s hit a few important factors, including those that Randy had to consider with his project. We’ll start with a few important decisions you need to make. Commercial purchase or homebrew? There are many, many fine commercial antennas on the market for VHF/UHF operations. I use three or four different ones in my home and in portable station operations of various types. Most commercially available antennas are going to provide great performance and even greater convenience! In virtually all cases you can simply buy-and-install with only the requirement of connecting a feed line to the antenna. If you want to open the wallet instead of the tool box, a commercial antenna is your best choice. For a typical dual-band “base” VHF/UHF antenna designed for exterior mounting on a structure or mast you can expect to pay anywhere from several dozen dollars to several hundred, depending on quality, durability, and performance factors such as gain. But if you’re the crafty type and enjoy a good challenge, you may want to homebrew your own antenna. There are many simple designs provided by a whole world of hams to choose from. For instance, the J-Pole antenna design for 2-m/70-cm ops is a very popular homebrew project, and it can be created with simple aluminum from the hardware store or even from segments of twin lead feed line. Even easier to construct is a single-band, half-wave dipole, and you can also find plans online for 2-m/70-cm dual band dipoles. Yagi directional antennas for VHF ops are great projects, if you seek that directional boost in signal gain for your situation. With a homebrew solution you can save some money, but be prepared to invest the time and effort necessary. And remember, every antenna is a compromise, so carefully check out the design and performance reports before finalizing your decision. Single band or multi-band antenna? With multi-band radios now so readily available to hams, the majority of folks are likely to desire a multi-band antenna with which a single feed line can be used. Probably the most popular combination is the 2-m/70-cm dual band scenario mentioned above, but tri-banders that include the 1.25-meter (220 MHz) band or the 6m (50 MHz) band are very popular, as well as combinations of 2-m/1.25-m, and other combinations. I highly recommend a dual band radio and antenna for the new Technician Class ham as a starter radio, most typically the 2-m/70-cm combo with an antenna to match. However, if the only repeater you intend to use from your home is a 2m machine, and you have no interest in other VHF/UHF band operations, then a single band VHF antenna may be your choice. (Ditto for only 1.25-m, 70-cm, or 6-m band ops). Consider the local radio resources available to you and how you wish to use them, and then decide what band capability your station and antenna require for those operations. Antenna location? The type of antenna you obtain and even the specific model or design will likely be influenced by your chosen mounting location. Many hams who live in covenant protected neighborhoods like to mount antennas in the attic to keep them out of sight. The height of your antenna may be limited by your attic’s apex, and some signal attenuation may be expected from roof materials, so an antenna that exhibits at least modest gain may be desirable. If you plan to mount your antenna outdoors you may wish to ensure you get a sturdy model that can withstand high winds and implement moisture protection at the coaxial cable feed point. If you mount in a tree, be sure the motion of tree and limbs will not damage or dislodge the antenna. Location and antenna selection are closely coupled, so think it through before you purchase or brew. Antenna gain? Depending upon your situation you may need a little boost in your effective radiated power, or the effective signal strength from your antenna. Many antennas provide signal gain, boosting the effective transmit power at the antenna. If you live quite a distance from a repeater that you’d like to use, and if your transmitter is somewhat limited in its power output, a high gain antenna may help your signal make it there. Antenna gain is defined in comparison to a reference antenna. Comparing antenna gain to a half-wave dipole is common, and the gain is designated in decibels with the unit reference dBd (the last ‘d’ for ‘dipole’). A model isotropic antenna is also a common reference point, designated by dBi (‘i’ for isotropic), in which the radiated power is a perfect spherical pattern. Recall from Technician License studies that a 3 dB increase or decrease is a factor of 2 ratio comparison. So, an antenna offering 3 dBi will provide double the signal strength (in its main lobe transmission pattern) as compared to the same transmission with the theoretical isotropic antenna that radiates equally in all spherical directions. If your antenna specification says 6 dBd, it provides main lobe gain 4X (2X + 2X) that of a dipole antenna. For a typical commercial vertical VHF/UHF antenna the gain will usually be compared to the isotropic reference. The signal pattern from such antennas tends to be disk-like in a horizontal omnidirectional pattern, 360 degrees around the antenna toward the horizon. So, the signal strength that the theoretical isotropic antenna would spew in every direction of the spherical pattern is vertically squeezed into this horizontal disk pattern, providing relative signal gain over the isotropic pattern. A dipole antenna produces lobes with the strongest signals at right-angles to the radiating element orientation. The weakest signals are out the ends of the radiator. So, a dipole has gain as compared to the spherical isotropic antenna pattern. Thus, when your VHF/UHF antenna is compared to a dipole (dBd gain figures), it is being compared to a higher performing standard than the isotropic reference. Pay attention to whether the gain is expressed as dBi or dBd when comparing antenna performance, and realize that a lower gain figure in dBd may actually be better than a higher figure in dBi. Compare apples to apples, oranges to oranges. [Note, a dipole exhibits about 2.15 dB gain relative to the isotropic case, so antenna comparisons to the dipole (dBd) will be 2.15 dB lower than comparisons to the isotropic antenna for the same actual gain produced.] Lastly regarding gain, if you choose a directional antenna like a Yagi with high gain in one pointing direction (but not omnidirectionally), you will usually want to plan for a mounting scheme that allows for rotating the antenna. A directional VHF/UHF antenna can help you reach out and tag that distant station, but unless you can readily rotate it you’re very limited in your direction of strongest propagation. Additional Considerations? Other antenna factors that you may want to consider include the height at which you mount your antenna (generally, higher is better), the mounting method you plan to use (mast, tree, attic clamp, strap to chimney, etc.), the length of coaxial cable necessary to reach the location from your transceiver (consider transmission line loss), and the polarization you desire (vertical for most FM ops, horizontal for SSB). If you go for that Yagi directional for FM ops, don’t forget to mount it with the elements running vertically instead of horizontally. If you need a 100 foot run of coax to get to your antenna, you’d better check your coaxial cable loss figures, as we’ll discuss below. Some Coaxial Cable Considerations Impedance: It is very important to select coaxial cable with a characteristic impedance that matches your transmitter output and your antenna feed point impedance. For VHF/UHF commercial antennas you are virtually guaranteed to have something close to a 50 ohm feed point as long as you keep the antenna away from other significant conductors in the environment by a wavelength or two. (You probably don’t want to mount your vertical antenna right next to the vertical aluminum downspout on your house, for instance.) But virtually all Amateur Radio VHF/UHF transmitters and antennas are designed for 50 ohm coaxial cable, and there are many varieties of 50-ohm coax to choose from. How do you know what to get? Feed Line Loss: One of the chief factors to consider in selecting coax is its loss figures. As signals travel along the conductors they will be attenuated. Higher frequency signals will have more loss in the transmission line than lower frequency signals, and different designs of coax cable will impose different magnitudes of loss overall. It is easy to compare loss figures among various coaxial cables – most distributors or manufacturers will publish the cable’s loss figures for various frequencies. The most common comparison metric is loss in decibels per 100 feet of cable, like the table here. Notice that for RG-58/U type cable at 100 MHz (close to the 2m band frequency range) the loss for 100 feet of transmission line is 3.8 dB. That means that at the antenna feed point your transmitter’s signal power will be less than one-half its indicated value on your transmitter (-3 dB = 0.5 power... a factor of 2 decrease). Generally, lower loss cable types are more expensive than higher loss – you get what you pay for. But if you have a short run of only a couple dozen feet to reach your antenna, the loss may not be that significant and you can save your money. If you have a longer run, more than 50 feet, you may find it advantageous to pay a little more and preserve your effective signal strength at the antenna. Further, you should also consider the gain of the antenna you select along with the loss imposed by the coax. While the comparison or compensation of antenna gain for feed line loss isn’t necessarily an apples-to-apples situation, you can get a general idea of the combined effects of pairing various cables/lengths and antennas when scheming on your antenna system design. Coaxial Cable Gauge: How and where you need to route your antenna coaxial cable and the length of run necessary may impact your selection of a coaxial cable gauge, or diameter. Narrow gauge coax such as RG-58 or RG-174 is low profile and quite flexible. It requires smaller holes and it fits around corners well. However, as noted in the table above, narrow gauge cables tend to impose higher signal losses. Larger gauge coax, such as RG-8, 9913, or LMR 400 is much more noticeable and is usually stiffer and somewhat more difficult to work with. However, the larger gauge cables tend to offer the lowest loss figures. Additionally, some of these larger diameter cables are produced in flexible varieties, such as Belden 9913F7. It combines very admirable loss figures with high flexibility for ease of routing, but it is limited in its power handling capacity to about 300 watts. Still, for most VHF/UHF FM operations this capacity is much more than adequate. Consider the coaxial cable routing for your potential antenna locations and identify the best combination of cable type for location, routing, and loss. Some Connector Considerations Common Connectors: A few of the most common connectors used in amateur radio are: PL259 / SO239 – The PL259 is the male connector while the SO239 is the female counterpart. This connector is sometimes referred to as a “UHF connector,” even though its performance at UHF frequencies is not that stellar. This connector combo is very commonly found on mobile and base station antenna connections, and it serves very well in the HF and UHF ranges. You can obtain PL259 connectors for most of the coaxial cable gauges, although they usually will not be coupled with the narrowest gauge cables such as RG-316 or RG-174. N-Connector – The N-connector has excellent performance into the UHF range, although it is rarely found at the coax connect point on transceivers. The N-connector offers better protection against water intrusion than the PL259. SMA Connector – The small SMA connector is very popular on modern HTs, and it offers very good performance into the UHF range and higher frequencies. It is comfortably coupled with even the smallest diameter cables. BNC Connector – This older connector is less commonly used with the advent of the SMA, but it will still be found on some products and older HT radios. It offers good performance for VHF and UHF, and it is mechanically very solid. Adapters: Converting from one connector type to another can be done with adapters. Almost every conceivable combination is available as single adapters or as short cables with differing connectors on opposite ends. A common adapter is PL259 / SMA combination. With this connector you can readily attach a home antenna system to an HT radio that uses the SMA connector, or dispense with the adapter to connect the PL259 feedline connector into a base station transceiver. Barrel connectors are also useful for extending a cable’s length or connecting two male-type connectors via a dual-female barrel. Randy’s Solution Antenna: Randy wanted to go with an inexpensive commercial antenna, specifically a dual band 2m/440 product. He wasn’t too concerned with high gain, as he was able to hit several area mountaintop repeaters with his HT, and he probably needed just a little more height to get over the hilltop for our local community machine. So, he was willing to trade off high gain for low expense. He also had to consider his neighborhood HOA covenants that prohibit highly visible external antennas. His first preference was to try an attic antenna over his garage and close to his home office operating position. This option provided the shortest coaxial cable length requirements as well, but it was unclear what kind of attenuation he would get from his roof materials. His backup option was to mount a low profile rooftop antenna, strapped to a chimney box, positioned such that it was not obviously visible to surrounding neighbors. This higher, exterior location should provide improved performance over the attic option, if needed. The attic option imposed a height restriction on the antenna of 66 inches maximum, and if the rooftop exterior option was necessary Randy wanted a low profile antenna. After evaluating several commercial options he selected the Arrow OSJ 146/440 J-Pole antenna. A J-Pole offers about the same gain performance as a half-wave dipole (about 2 dBi). It is a simple, inexpensive antenna, and this specific antenna stands about 60 inches high. Randy’s approach was a common one in ham radio: Let’s just try it! We would try the J-Pole in the attic location first and see if the performance was acceptable in that configuration, and we would go for the more difficult rooftop location only if necessary. Feedline: The coax run from the attic location, along the ceiling and down a wall was about 50 feet total, and Randy had purchased 60 feet of Belden 9913F7. He examined several varieties of coax cable and settled on the 9913F7 due to it’s moderate expense, its flexibility for making tight turns, and its good loss performance in the 440 MHz range (2.8 dB/100’ at 400 MHz) – the local community repeater is in the 70 cm band. Since he planned to use his 5 watt HT initially with the antenna system and would not have a higher power transmitter until later, keeping the transmission line loss low was a key consideration. Using the fully available 60 feet of this cable we estimated the loss to be approximately 1.8 dB in the 70 cm band. This would attenuate his 440 MHz effective power at the antenna by about 1/3, or resulting in about 3.3 watts at the antenna with the HT. Given the additional attenuation by the roofing materials, we were dubious that the attic solution was going to be sufficient! Connectors: Randy purchased the coaxial cable prefabricated, or with connectors already attached. Because the J-Pole antenna was available with an SO239 only, and because most mobile/base transceivers also use the SO239 connector, Randy selected the male counterpart PL259 connectors for each end of the coax segment. Although the N-connector tends to offer better performance for UHF, this was not an option for this antenna. Once again, a bit more loss was to be expected for the UHF transmissions! Still, we would just try it and see! Finally, Randy used a cable adapter as pictured above with an SO239 connector on one end and an SMA connector on the other to attach the antenna to his HT. Results: Randy mounted the J-Pole in a temporary configuration in the attic just adjacent to the garage pull-down stair access. He routed the coaxial cable down into the garage and connected to the HT. I listened from my truck’s mobile station as he pushed-to-talk to the community repeater. It worked! Randy hit the repeater with a moderately strong and perfectly readable signal. Although not full quieting with just a mild “popcorn” static behind his audio, the signal was clear, steady, and completely readable. We traded positions so that Randy could hear the signal from his new antenna, and he deemed it quite good enough. Subsequently, Randy installed the J-Pole with more permanent mounting to a rafter in the attic. He routed the coaxial cable above the ceiling and down the garage wall, and then into his office with a nice cover plate on the interior wall. He’s been on the air reliably ever since, and we hope it doesn’t require another emergency to test the robustness of his rig again! Nice job Randy! Now, let’s talk about that base station… Stu WØSTU

The 2022-2026 Technician License Exam question pool asks how coaxial cable losses and signal frequency are related: T9B05: What happens as the frequency of a signal in coaxial cable is increased? A. The characteristic impedance decreases B. The loss decreases C. The characteristic impedance increases D. The loss increases Coaxial cable is the most commonly used type of amateur radio transmission line, or feedline, because it is easy to use and requires few special installation considerations. Coaxial cable can be effectively used from HF through VHF and UHF frequencies common in amateur radio, but every ham should be familiar with the characteristics of coax and understand its limitations, particularly as frequency increases into the UHF range. That’s what this question is getting at. Coaxial cable can impose some significant loss in signal strength compared to other types of feedlines, such as ladder line or twin-lead. There are two primary causes of signal loss with coax: 1) Resistive loss, and 2) Dielectric loss. Resistive loss arises from the resistance of the center conductor of the cable and results in dissipated heat. Radio frequency currents tend to flow along and near the surface of conductors. This is known as the skin effect. The greater the surface area of a conductor, the lower the resistance, and vice versa – small surface area means higher resistance. As signal frequency increases the skin effect becomes more pronounced. That is, the “depth” within the conductor through which currents flow becomes reduced as frequency increases. As these higher frequency signals are squeezed closer and closer to the surface of the conductor, the effective cross-section area of the conductor through which they may flow is decreased. When the current flow area is decreased the electrical resistance increases. (Think of the water analogy, in which the pipe is narrowing through which the current may flow.) Resistive loss has a significant effect even down in the HF frequency range. Dielectric loss refers to signal loss resulting from some complex interactions of the alternating electric field with the insulating material that separates the center conductor from the surrounding shield in the coaxial cable. Generally, the more dense the insulator the greater the dielectric loss that results. For frequencies in the HF range, dielectric loss is usually not significant for most coaxial cable constructions. However, as frequencies increase into the VHF range, and even more significantly into the UHF range, dielectric loss becomes quite significant with most coax insulating materials. So, as signal frequency increases the loss increases due to both resistive and dielectric loss characteristics. But resistive loss dominates in the HF range, and dielectric loss begins to become significant in the VHF range. In the UHF range these two characteristics are adding together to produce large loss values in many types of coax. Remember, the denser the dielectric insulating material the greater the dielectric loss. And the lower the conductor surface area (smaller diameter conductor) the greater the resistive loss. So, a very low density insulating material, such as air, combined with a large surface area center conductor, such as a large diameter multi-strand copper conductor, will produce the lowest loss figures for coax. The air insulated hard line provides just such a combination and the lowest loss characteristics of any type of coaxial cable. Signal loss is measured in decibels of power. Below is a table of some typical coax types and their loss figures for given frequencies. Each value is the loss in decibels per 100 feet of coax length. Notice how in each cable type the loss per 100 feet increases with signal frequency, and notice that the magnitude of increase gets larger in the 400 MHz (UHF) range. The answer to Technician question T9B05, “What happens as the frequency of a signal in coaxial cable is increased?” is D: The loss increases. -- Stu WØSTU