Grey or gray line propagation is a form of HF radio propagation apparent at dawn and dusk where signals traveling along the line are heard at much higher strengths.
Grey line or gray line propagation is a form of radio signal propagation that provides surprisingly long distance radio communications at dawn and dusk sometimes when other forms of ionospheric propagation may not be expected to provide signal paths of these distances.
Grey line propagation is only present around dawn and dusk and therefore it cannot be used to support global radio communications at any time. Accordingly it tends to be used chiefly by radio amateurs and a few other users who can accommodate the timing and other limitations of its availability.
For grey line propagation signals travel along the grey or twilight zone between night and day. This is area where night and day meet and it is also known as the terminator. In this region signals on some frequencies are attenuated much less than might normally be experienced and as a result signals can be received at surprisingly high levels over very long distances – even from the other side of the globe.
The improved propagation conditions around the grey line are most noticeable primarily on the lower frequency bands in the HF portion of the spectrum where the level of ionization in the D layer has a much greater effect on signals that on those frequencies higher up.
The diagram below shows how the illumination remains on the F region much longer than on the D region, and this creates a situation where the D region has faded away, but the F region remains intact.
In reality, the D region fades before dusk as the illumination from the sun reduces around dusk at the Earths surface. The level of ionization in the D region drops very quickly around dusk and after dark because the air density is high and recombination of the free electrons and positive ions occurs comparatively quickly.
This occurs while the level of ionization is still high within the F layer, which gives most of the radio propagation for long distance radio communications. This occurs because the F region is much higher in altitude, and as the Sun sets it remains illuminated by the Sun’s radiation for longer than the D region, which is lower down. Also recombination of the ions takes longer because the air is very much thinner at the altitude of the F region compared to that of the D region.
The same occurs in the morning as the Sun rises. The F region receives radiation from the Sun before the D region and its ionization level starts to rise before that of the D region. As the level of the D region ionization is low, this means that the degree of attenuation to which the lower frequency signals are subjected to is very much less than in the day. This also occurs at a time when the F region ionization is still very high, and good reflections are still achievable. Accordingly this results in much lower overall path losses around the grey line than are normally seen.
In terms of the diagram above, the altitude of the D and F regions have been highly exaggerated to show the mechanism behind the grey line. This means that the fading of the D region starts to occur well before dusk and the F region remains in place until after dusk – and grey line propagation occurs around the region of dusk and dawn.
In fact, when looking at the region of the radio terminator it should be remembered that there are a variety of variables that mean that it does not exactly follow the day time / night time terminator as seen on the Earth’s surface. The ionized regions are well above the Earth’s surface and are accordingly illuminated for longer, although against this the Sun is low in the sky and the level of ionization is low. Furthermore there is a finite time required for the level of ionization to rise and decay. As there are many variables associated with the “radio signal propagation” terminator, the ordinary terminator should only be taken as a rough guide for radio signal propagation conditions.
Although it may be obvious to mention, grey line propagation can only exist for stations at locations that fall along the grey line or terminator. This significantly limits the number of areas for a given station at a particular location to set up long distance communication, although there will be slight changes over the course of the year for many stations.
Frequencies that are affected by this form of propagation are generally limited to frequencies up to about 10 MHz. Frequencies higher in frequency than 10 MHz tend to be attenuated to only a minor degree by the D region and therefore there is little or no enhancement around dusk and dawn by this mechanism.
Grey line propagation is particularly noticeable on lower frequencies, for example the 3.5 MHz amateur radio band. Normally signals may be heard over distances of a few hundred kilometers in the day, and possibly up to or two thousand kilometers at night for those stations with good antennas.
Grey line propagation regularly enables long distance radio communication contacts to be made with stations the other side of the globe at very good strength levels.
The optimum times are normally around the spring and autumn equinoxes as neither end of the link is subject to the propagation extremes of summer and winter. It is at these times of year that long distance radio communication can be established with stations on the other side of the globe at remarkably good signal strength levels.
It is still possible for higher frequency signals to be affected by a grey line type enhancements. This occurs as a result of the fact that a propagation path is opening in one area and closing in another giving a short window during which the path is open on a particular frequency or band of frequencies.
Looking at the MUFs over the course of the day can demonstrate the way in which this occurs. The level of ionization in the F layer falls after dusk, and rises at dawn. This results in the MUF falling after dark.
Accordingly, stations experiencing dawn find the MUF rises and those experiencing dusk find it that it falls. For frequencies that are above the night time MUF, and for stations where one is experiencing dusk and the other dawn, there is only a limited time where the path will remain open. This results in a similar effect to that seen by the lower frequency grey-line enhancement.
The path of the grey line changes during the course of the year. As the angle subtended by the Sun’s rays changes with the seasons, so the line taken by the terminator changes. This results from the fact that during the winter months, the Northern Hemisphere of the earth is titled away from the Sun, and towards it during the summer months.
The converse is obviously true for the southern hemisphere. In addition to this the width of the grey line also changes. It is much wider towards the poles because the line between dark and light is less will defined as a result of the fact that the Sun never rises high in the sky at the poles. It is also much narrower at the equator. This results in grey line propagation being active for longer at the poles than at the equator.
Grey line propagation provides an opportunity for long distance radio communication contacts and links to be made, often with stations the other side of the globe. Signals travel along the grey line, or terminator and suffer comparatively little attenuation. An opening via grey line propagation may only last for half an hour, but it gives the opportunity for radio communication to be established between stations as far away as the other side of the globe.
Attention D1 Emergency Coordinators. If you would like to post any Public Service announcements or upcoming Events on the District 1 Website public service page, just send an email to Mark, KC7NYR and I will get your event posted or use the contact page with the request.
This service is open to all Counties in District 1 Counties; Clackamas, Clatsop, Columbia, Multnomah, Tillamook, Washington.
If you like me to also make announcements on the D1 Net about your upcoming Event, just let me know and I would be happy to do this on your behalf.
Public Service Page
To contact as many stations as possible on the 160, 80, 40, 20,15 and 10 Meter HF bands, as well as all bands 50 MHz and above, and to learn to operate in abnormal situations in less than optimal conditions.
Field Day is open to all amateurs in the areas covered by the ARRL/RAC Field Organizations and countries within IARU Region 2. DX stations residing in other regions may be contacted for credit, but are not eligible to submit entries.
Each claimed contact must include contemporaneous direct initiation by the operator on both sides of the contact. Initiation of a contact may be either locally or by remote.
ARES District 1 Net meets daily for the purpose of preparation and coordination of District 1 ARES communications in the event of an actual emergency.
Net Information: Meets Daily 7:30-PM-8:00PM on the linked K7RPT Repeaters, Our primary repeaters are the 147.32, 442.325, 444.400 and 147.04 megahertz linked repeaters all having a 100hZ tone, also the 146.72 megahertz repeater on Wickiup Mountain with a 114.8 hz tone. We also have an alternate repeater on 146.84 megahertz.
We meet 7 days a week 365 days a year. There are 7 Regular Net Control Stations and 14 active Alternate Net Control Stations. We also have an additional 13 inactive alternates that can be activated at anytime.
The D1 Net Control Schedule is updated and maintained by Mark, KC7NYR the Assistant Net Manager and Net Secretary and also Hal, KC7ZZB the Net Manager. If your interested in becoming an Alternate Net Control Station, just contact KC7NYR or KC7ZZB and we will get you set up.
Recently a student in our Technician License Class realized that it may take quite a few antennas to cover all of the available ham bands. He asked, “So how many antennas do I need?”
Of course, my answer was “you can never have too many antennas.”
This is a very valid question. Radio amateurs have so many bands available to them, it does present a challenge to figure out the antenna situation. Someone recently said to me, “getting the radio is the easy part — figuring out the antennas is the real challenge.” So true.
A new Technician often decides to just focus on VHF/UHF with an emphasis on FM simplex and repeater operation. The focus of this article is broader than that, with the addition of HF operation. Keep in mind that a Technician Class license gives you access to all of the VHF/UHF bands and a relatively small slice of the HF bands (10 meter phone plus 80m, 40m, 15m and 10m CW). The General Class license provides greatly expanded privileges on HF. Imagine that you just bought one of those “do everything rigs” that cover all of the HF bands, 6m, 2m and 70 cm (e.g., Yaesu FT-857, FT-991, Kenwood TS-2000, or Icom IC-7100). That’s a lot of spectrum to cover and no single antenna will do it all efficiently.
DIamond X-50A Dual-Band Antenna (2m+70cm)
A basic antenna setup for such a station is to use a dualband VHF/UHF antenna to cover 2m and 70cm, along with a multi-band HF antenna. This won’t actually result in an antenna system that covers all of the ham bands, but it can be a good start.
The dual-band VHF/UHF antenna could be a Diamond X-50A, a Comet GP-3, or similar antenna. Another popular design is the Arrow Open Stub J-Pole antenna. These antennas are vertically polarized, covering basic 2m and 70 cm simplex and repeater operating. They won’t do a good job with weak-signal SSB or CW operating, where horizontal polarization is preferred. Some folks may argue for just putting up a single-band antenna for 2m only, which is the most popular VHF band.
For operating on the HF bands, you’ll want an efficient antenna that covers multiple bands. You could put up single-band antennas for every band, but that gets complicated and typically results lots of antennas and lots of cable runs back to the ham shack. Focusing on the new ham, it makes sense to go for a multiband antenna and keep the number of individual coaxial cable runs to just a couple.
The first question that pops up is “which bands?” Well, that depends. My biases are towards the higher bands (20m and up) because I like to work other countries around the world during daylight hours. If you are more interested in North American contacts, especially in the evening hours, you might want to cover the 40m and 80m bands. For a new ham, this may be difficult to figure out, until you get some experience and discover your preferred ham bands.
So, a good compromise for the new HF operator is a multiband antenna that allows operations on a couple of higher bands (perhaps 20-meters, 15-meters, and/or 10-meters), and operation on at least one lower band (perhaps 40-meters and/or 80-meters). Some reasonably inexpensive commercial options with such band allowances are readily available as horizontal wire fan dipoles or trap dipoles. Let’s consider these options:
Fan Dipole (also known as a parallel dipole) – This is a half-wave dipole with additional elements added to cover additional bands. While there is some interaction between the different dipole elements, they are normally fed by a common coaxial cable, avoiding the need for multiple cable runs.
A fan dipole configures multiple dipoles trimmed to different bands using a single feedline. (Not to scale)
Trap Dipole – This antenna uses tuned circuits (“traps”) to enable a single dipole to operate on multiple bands. The dipole length is determined by the lowest frequency band and the traps are used to electrically shorten the dipole for higher bands. Trap antennas can usually be designed to work well with two or three different HF bands, and designs combining fan and trap dipole features can provide more, with some trade-offs in efficiency and performance.
A trap antenna has resonant circuits inserted in the radiating element that electrically shorten the antenna for use at higher frequencies. (Not to scale)
End Fed Half Wave (multiband) – This half-wave antenna is similar to a dipole but the coaxial cable is connected to one end of the half wave wire, allowed easier mounting than the typical center-fed dipole. A well designed matching transformer at the end feed point facilitates this antenna configuration. Multiband versions of this antenna exist and are a convenient way to enable several bands at once. The popular Vibroplex Par EndFedZ® product line offers several multiband options.
The Vibroplex EndFedZ EF-Quad antenna operates well on 10m, 15m, 20m, and 40m bands. It is 65 feet long, uses three short stub extensions along the length, and has an end-of-wire feed point transformer with coaxial connector. (Courtesy Vibroplex, Inc.)
Multiband vertical – Quite a few different vertical antenna designs support multiple bands. For example, see the
Cushcraft R9 Multiband Vertical Antenna (Courtesy Cushcraft, Inc.)
or R9, GAP Challenger DX, Butternut HF9V and the Hustler 4BTV. When considering a vertical antenna, pay attention to whether the design requires ground radials to be installed. Nothing wrong with them, but radials can be critical to achieving efficient antenna performance. If you have restrictive covenants, you might consider a vertical antenna that is also a flag pole (really!). Take a look at ZeroFive Antennas for examples.
Antenna Tuners – When trying to cover lots of bands with just a few antennas, an antenna tuner will be really handy. This may be built into your radio or it may be a separate box inserted into the feedline between the transmitter and antenna.
An antenna tuner does not actually “tune your antenna” but it will tweak up the SWR of the antenna and allow it to be used across a broader range of frequencies. It also will keep your transmitter happily perceiving a nice 50-ohm feedline impedance that circumvents automatic power reductions that come with high SWR from an impedance mismatch.
Other Bands and Modes I’ve focused on the most popular ham bands, but there are many other frequencies to consider. The 6-meter band is a lot of fun and is accessible to Technicians. Most of the time, this band is good for local communication but it often opens up for over-the-horizon skip by sporadic-e propagation, especially during the summer months. Some of the multiband HF antennas mentioned above also cover 6 meters, or you can put up a separate 6m dipole to get started. The more serious 6m operators use a Yagi antenna to produce gain and a big signal. In most station configurations, a separate 6-meter antenna will dictate another dedicated coaxial cable run.
Another fun mode is 2m single sideband (SSB), the workhorse band for weak-signal VHF. You’ll need a horizontally-polarized 2-meter antenna, preferably with some gain. The most common antenna used is a Yagi with many elements, such as the M2 2M9SSB antenna or the portable Arrow models.
So, How Many? – You can make a lot of contacts and construct a superb HF to UHF station with just two quite simple antennas. The VHF/UHF vertical dual-band antenna paired with a multiband horizontal wire dipole is a cost-efficient, easy-to-erect combination providing FM simplex and repeater ops for local communications as well as long-distance HF skip on several bands. It’s a very good way to start.
Putting together an antenna system can seem like an overwhelming task for the beginner, so don’t get too freaked out about it. The main thing is to get something usable up in the air and make some contacts. Over time, you will probably add or change your antennas to get just what you want. That is part of the fun of amateur radio.
Ground wave propagation is a form of signal propagation where the signal travels over the surface of the ground, and as a result it is used to provide regional coverage on the long and medium wave bands.
Ground wave propagation is particularly important on the LF and MF portion of the radio spectrum. Ground wave radio propagation is used to provide relatively local radio communications coverage, especially by radio broadcast stations that require to cover a particular locality.
Ground wave radio signal propagation is ideal for relatively short distance propagation on these frequencies during the daytime. Sky-wave ionospheric propagation is not possible during the day because of the attenuation of the signals on these frequencies caused by the D region in the ionosphere. In view of this, radio communications stations need to rely on the ground-wave propagation to achieve their coverage.
A ground wave radio signal is made up from a number of constituents. If the antennas are in the line of sight then there will be a direct wave as well as a reflected signal. As the names suggest the direct signal is one that travels directly between the two antenna and is not affected by the locality. There will also be a reflected signal as the transmission will be reflected by a number of objects including the earth’s surface and any hills, or large buildings. That may be present.
In addition to this there is surface wave. This tends to follow the curvature of the Earth and enables coverage to be achieved beyond the horizon. It is the sum of all these components that is known as the ground wave.
Beyond the horizon the direct and reflected waves are blocked by the curvature of the Earth, and the signal is purely made up from the diffracted surface wave. It is for this reason that surface wave is commonly called ground wave propagation.
The radio signal spreads out from the transmitter along the surface of the Earth. Instead of just traveling in a straight line the radio signals tend to follow the curvature of the Earth. This is because currents are induced in the surface of the earth and this action slows down the wave-front in this region, causing the wave-front of the radio communications signal to tilt downwards towards the Earth. With the wave-front tilted in this direction it is able to curve around the Earth and be received well beyond the horizon.
Effect of frequency on ground wave propagation
As the wavefront of the ground wave travels along the Earth’s surface it is attenuated. The degree of attenuation is dependent upon a variety of factors. Frequency of the radio signal is one of the major determining factor as losses rise with increasing frequency. As a result it makes this form of propagation impracticable above the bottom end of the HF portion of the spectrum (3 MHz). Typically a signal at 3.0 MHz will suffer an attenuation that may be in the region of 20 to 60 dB more than one at 0.5 MHz dependent upon a variety of factors in the signal path including the distance. In view of this it can be seen why even high power HF radio broadcast stations may only be audible for a few miles from the transmitting site via the ground wave.
Effect of the ground
The surface wave is also very dependent upon the nature of the ground over which the signal travels. Ground conductivity, terrain roughness and the dielectric constant all affect the signal attenuation. In addition to this the ground penetration varies, becoming greater at lower frequencies, and this means that it is not just the surface conductivity that is of interest. At the higher frequencies this is not of great importance, but at lower frequencies penetration means that ground strata down to 100 metres may have an effect.
Despite all these variables, it is found that terrain with good conductivity gives the best result. Thus soil type and the moisture content are of importance. Salty sea water is the best, and rich agricultural, or marshy land is also good. Dry sandy terrain and city centres are by far the worst. This means sea paths are optimum, although even these are subject to variations due to the roughness of the sea, resulting on path losses being slightly dependent upon the weather! It should also be noted that in view of the fact that signal penetration has an effect, the water table may have an effect dependent upon the frequency in use.
Polarisation & ground wave propagation
The type of antenna and its polarisation has a major effect on ground wave propagation. Vertical polarisation is subject to considerably less attenuation than horizontally polarised signals. In some cases the difference can amount to several tens of decibels. It is for this reason that medium wave broadcast stations use vertical antennas, even if they have to be made physically short by adding inductive loading. Ships making use of the MF marine bands often use inverted L antennas as these are able to radiate a significant proportion of the signal that is vertically polarised.
At distances that are typically towards the edge of the ground wave coverage area, some sky-wave signal may also be present, especially at night when the D layer attenuation is reduced. This may serve to reinforce or cancel the overall signal resulting in figures that will differ from those that may be expected.
You’ve probably heard the term “Q factor” tossed around in describing antennas, but maybe you haven’t quite yet picked up on exactly what it means from a practical standpoint. Let’s see if we can get at Q, or quality factor, as it relates to antenna circuits and amateur radio operations without reviewing any college level physics or higher math. When we’re done, you’ll have an intuitive understanding of Q that likely far exceeds that of the average ham.
In the grander picture beyond ham radio, the quality factor is a value that describes some characteristics of an oscillating or resonating system. In radio we’re mostly interested in electric circuits that do the oscillating, and an antenna circuit is of particular interest as oscillating circuits go. We’ll get to the practical upshot of an antenna’s Q factor shortly, but we can get a good sense of Q factor by thinking about some other kinds of oscillators, like a simple pendulum – a hefty weight hanging on the end of a long string, able to swing back and forth. Stick with me and we’ll get back to antennas with your exclamation of “Ahhhhhhh! I get it!” in just a moment.
Q factor defines the damping of a resonator. The pendulum in water is damped more than the same pendulum swinging in air.
Q factor defines the damping of a resonator. The pendulum in water is damped more than the same pendulum swinging in air.
Damping: Q factor defines the damping of a resonator. You may think of damping as how long it takes for an oscillator’s action to die out. Suppose with a single push you swing a lengthy and weighty pendulum that’s hanging in air from a high anchor point. Imagine a bowling ball strung up from the ceiling by a nylon cord. You push the ball up and then release it, and you count 200 back-and-forth swinging cycles until the bowling ball is perfectly still again. This pendulum oscillator is not damped very much, but the resistance of the air against the ball and perhaps a little friction at the anchor point delete a fraction of the initial energy you supplied with each cycle until the pendulum is again unmoving. The energy is lost slowly.
Suddenly, the plumbing fails dramatically and the room fills with water. Fortunately, you’re a good swimmer and you displace the bowling ball again to the exact same location as before and then release it. You count only a handful of back-and-forth swinging cycles before the bowling ball is stationary in its watery surrounding. The pendulum oscillator is now highly damped by the water’s resistance. It loses the imparted energy very rapidly.
Resonance: Suppose you want to keep the pendulum oscillating with its natural frequency of resonance. You have to add just enough energy each cycle to overcome the energy lost to the resistance. With the bowling ball suspended in air you could easily make up for the lost energy each cycle by providing just a tiny little push at a convenient spot in the swinging cycle, perhaps just as the ball peaks in height and begins downward along its arced path. It’s easy to maintain resonant oscillations this way. But in the water you would have to issue a rather forceful shove each cycle to make up for all the energy lost in a single back-and-forth swing! Reinforcing resonance ain’t so easy with a highly damped oscillator!
Q Defined: Q factor is defined as the ratio of the energy stored in the oscillator to the energy that must be imparted per cycle to keep the oscillator swinging consistently. That is, the energy of the initial lift and shove of the bowling ball compared to the energy of just one of your regular reinforcing shoves to keep the ball swinging to the exact same height (amplitude) each cycle. The energy you add with a shove each cycle is exactly the same as the energy lost to resistance each cycle. So, in an equation form it looks like this:
Q = 2π x Energy Stored / Energy Lost Per Cycle
(The 2π term is a mathematical convenience that keeps things simple, so we won’t worry with it.)
From this simple equation you can see that our bowling ball suspended in air is a high Q oscillator – the energy lost per cycle is quite small compared to the energy stored from that initial shove, so Q will be a relatively high value. On the other hand, the bowling ball pendulum in water is a very low Q oscillator since gobs of energy are lost per cycle as compared with the initial stored energy, resulting in a lower comparative value for Q.
Now, enough of this bowling ball absurdity and back to some serious antenna talk!
Loading coil and capacitance hat. Compliments Hi-Q-Antennas.
Back to Antennas: Energized antennas are oscillators too. Current surges back and forth in radiating elements and, just like a bowling ball dangling from your ceiling and flying back-and-forth, there is a natural resonant frequency for an antenna. When you trim an antenna’s length you are adjusting the resonant frequency by changing the distance that current has to flow from end to end of the element, and hence, the time required for it to do so!
The time required for current to surge back and forth along the element’s length can also be impacted by inserting components like coils (inductors) or capacitors. It’s sort of like cheating; inserting the components to make the antenna act like a much longer antenna than its true physical length. You may hear terms such as “loading coils” and “capacitance hats,” or a “loaded antenna,” simply meaning that such tricks have been used to fool the antenna into thinking it’s a bigger boy than its diminutive height or length indicates.
“So,” you now ask, “why are some antennas still really long if we can just load them up with coils and hats and keep them shorter?” Good question, and the answer is Q.
Q and SWR Bandwidth: Q factor has no units – no ohms or henry or amps or anything – just a number. And there’s more than one way to calculate Q for an antenna. We can’t practically use the equation listed earlier, but magical mathematical transformations provide us the following more practical definition of Q when applied to oscillators that have relatively high Q values (>>1), like most antennas:
Q = ƒc ÷ (ƒ2 – ƒ1)
…where ƒc is the frequency of resonance (the center frequency to which the antenna is trimmed), and …ƒ1 and ƒ2 are the frequencies above and below the center frequency to which the antenna will operate, or achieve and acceptable value of SWR. (Properly, this is where the frequency results in 3 dB of power loss compared to the center frequency power transfer, but you can also use the frequencies where SWR increases to 2:1 as a practical comparison measure between antenna systems.)
You’re probably starting to feel that “Ahhhhhh!” well up in your throat.
You see now, as in the SWR curve diagram below, that an antenna that operates well over a broad band of frequencies (ƒ2 – ƒ1) is going to result in a relatively low Q value. An antenna that operates well across only a very narrow range of frequencies is going to generate a relatively high Q value. Thinking back to our bowling ball pendulums, the high Q antenna (bowling ball in air) is going to oscillate very efficiently and requires only a little reinforcing energy from the transmitter when it is functioning near its resonant frequency. But if you tune away from the resonant frequency only slightly you are going to see rapidly rising SWR and reduced efficiency. That freely swinging bowling ball doesn’t like to be stopped or changed from its natural swinging frequency. Don’t try and reverse its path before it’s ready to do so!
On the other hand, while a low Q antenna is somewhat more damped and may require slightly more reinforcing energy, it can oscillate well across a much broader range of frequencies. Note, the bowling ball in water is an over-the-top extreme illustration of low Q. However, you can imagine that because the bowling ball loses energy so rapidly in the water, it would not be difficult to get it to move back-and-forth at frequencies other than its natural resonant frequency, given the force to drive it. Just shove it back and forth with a little greater effort at any rate you wish! It won’t be stubborn or knock you over with a high store of energy like the air pendulum.
Comparison SWR curves for a Low Q and a High Q antenna system. The 2:1 SWR bandwidth is used for comparison computations using associated frequencies.
Q, Physically Shortened, and Full Length Antennas: Again, our bowling ball illustrations are extreme cases, and with antennas the difference between high Q and low Q is not quite so starkly exhibited, but the effects are important! Here’s why, and here’s why every antenna is not loaded up with coils and hats to keep it short and convenient.
When an antenna is physically shortened for the desired operating frequency and a loading coil is added to help it resonate at that desired frequency anyway, the Q factor is increased. You may consider that the inductive coil’s effect is to reduce damping in the antenna circuit at the desired operating frequency. Generally, the greater the antenna loading the higher the Q factor, and thus, the narrower the SWR bandwidth of the antenna. But greater loading (higher Q) also allows physically shorter antennas for a given frequency.
The advantage of the low Q antenna is its efficient operation across a broad bandwidth, so a full length antenna is simple and effective and large, and great for home shack use. A full length half-wave dipole is an example, or a ¼-wave vertical with ground plane. For the HF bands these antennas may be many dozens of feet long, so mounting one atop the family van probably is not an option.
The advantage of a high Q antenna is its shortened length, so you’ll often see these mounted on vehicles for mobile HF operations. A loading coil and perhaps a disk, spoke, or swirly capacitance hat is the telltale sign of a vertical high-Q loaded antenna. They get the job done at or very near the resonant frequency of the loaded antenna.
Finally, you ask: “What good is a high Q antenna if you’re limited to only one amateur band and perhaps only a very narrow range of frequencies in that one band?” Yea, that would be sort of a drag, huh? Driving cross-country never able to leave 14.313 MHz. Never fear, there are common solutions.
Many high-Q mobile antenna manufacturers implement mechanized antennas that change the antenna’s resonant frequency itself! Although the SWR bandwidth is very narrow, the tuned operating frequency is made to always be the centered resonant frequency by changing the size of the loading coil as you tune from frequency to frequency, or band to band. Think of that sharp, V-shaped high Q SWR curve in the diagram above moving quickly up and down the band as you tune, or jumping to another band altogether to slide along with your tuning whim.
Usually this is implemented by using a movable tap on a large loading coil so that the number of turns used by the antenna changes commensurately with the desired operating frequency. The amount of loading is changed in this way depending on the operating frequency selected, thereby altering the antenna’s center resonant frequency. It’s a clever solution, if substantially more complex than a static wire or vertical radiator. Sometimes you’ll hear these referred to generically as “screwdriver antennas” due to a seminal design that employed an electric screwdriver motor component to move the tap up and down the coil. But several varieties are found on the amateur market by a variety of names.
High Q, low Q, and 10Q for reading. 10Q very much! I hope this helps you understand the world of loaded antennas a little better through the nature of Q. Good luck, 73,
I am guessing that most of you reading this have either heard about FT8 from fellow Hams or heard it on air as that strange repetitive buzzing sound between the CW and SSB portions of the bands. As one of the fastest growing modes of Amateur Radio it has been hard to miss, but you may be wondering how to get started and why you would want to?
First, what is it? FT8 is one of the many digital modes often referred to as sound card modes (SCM) because they utilize a computer’s sound card to bring in audio from your radio to be processed by software to decode the information embedded in the signal. Conversely, when you want to transmit, the software encodes your message into audio tones that are sent out via your sound card to your radio’s audio or Mic input.
For years there have been a variety of these new software modes including Phase-shift keying (PSK31 & PSK 65), Hellschreiber, Olivia, Pactor, etc. and even older hardware-based modes such as RTTY that we now use our computers to encode and decode. FT8 is one of a group of Multiple Frequency-Shift Keying (MFSK) modes that include JT9, JT65 and MSK144 created by Joe Taylor, K1JT and co-developers.
FT8 is designed to maximize communication even when signals are very weak (as low as -24dB). This means that even low-powered stations and stations with sub-optimal antennas can make contacts worldwide. With its popularity, quickly working DXCC or WAS with FT8 is easily within reach of almost any station. With FT8, activity is limited to a narrow band of frequencies, so it is ideal for use with loop antennas that require retuning when changing frequency, such as CHAMELEON ANTENNA F-Loop 2.0 Portable HF Antenna (CHA-F-LOOP-2-0). FT8 is also extremely popular on the 6 meter band, so there are many opportunities for long-distance communication even with a Technician Class License.
To use FT8 you need four things:
Although you can operate FT8 with older transceivers, the best experience will come by using a transceiver capable of both computer control and dedicated data mode. Fortunately, most modern radios have both of these. The extra feature that many of today’s radios have is a built-in sound card, eliminating the need for the extra sound card interface. Many reasonably priced popular radios have this feature, including the ICOM 7300 (ICO-IC-7300), Yaesu Ft-991A (YSU-FT-991A) and Kenwood TS-590SG (KWD-TS-590SG). If you are looking for a mobile/base radio, the ICOM IC-7100 HF/VHF/UHF (ICO-IC-7100) also has these features at a bargain price.
If your current radio does not have a built-in sound card interface, there are a few easy to use commercial devices available. The Tigertronics SignalLink™ USB Interface Unit is very popular. DX Engineering can provide you a SignalLink™ unit with a prebuilt cable to match most existing radios. Just choose one of the 16 part numbers for the combo designed for your radio, attach the interface cable to your radio, and connect a single USB cable to your computer. You are then ready to go not only for FT8 but also PSK31, JT65, JT9, FSK441, MSK144, WSPR, RTTY, SSTV, CW, Olivia, EchoLink Node and many more with appropriate software.
Another option is the MFJ 1204 Series USB Digital Mode Interfaces. Again, choose one of five part numbers for interface and cable combos from DX Engineering to match your rig, connect to the radio, connect a single USB cable to your computer, and you are ready to go.
WSJT-X is the most popular software for FT8. This great program is not only free but versions are available for Windows-based PCs and Macintosh OS, Linux (with pre-compiled Debian, Fedora and Raspbian distros). For details on installing and configuring the software, follow the onlineWSJT-X User Guide. Do not ignore the information on making sure your computer’s time is synchronized as this is vital to making contacts! After you install the software, you may also need to configure your radio’s settings.
An excellent guide on operating is “FT8 Operating Guide Weak Signal HF DXing … Enhanced” by Gary Hinson ZL2iFB. Don’t forget to join the WSJT Meteor Scatter and Weak Signal Yahoo Group for up-to-minute information on FT8. Free helper software programsJTAlert (or for Linux AlarmeJT) provide many additional features for FT8 operations. For additional information on a wide variety of digital modes and software visit www.k8zt.com/digital.
Source Credit: On All Bands
FT8 Digital Amateur Radio: A Complete Website with step by step Instructions with pictures.