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The Worry and Apprehension of VHF Antenna Polarization
By John Wendt, WA6BFH While this article will primarily address the bands of 10 and 6 Meters, I will add some thoughts on other VHF and UHF wavelengths as we get into the meat of the issue.
Probably the first wavelength band that I need to address is in reference to my mention of 10 Meters! You see 6 Meters is often referred to as the “Magic Wavelength Band”; and this is because it often works like an HF wavelength band, when it is in fact a VHF band. Well 10 Meters, an HF band, often works like a VHF band in terms of its signal propagation. So I guess some of that magical pixie dust has just sprinkled on down frequency almost one octave!
Now with this next band, 6 Meters, I have lots of experience, about 38 years worth! It is a truly magic band, although I feel the same way about several bands above it! Anyway, 6 Meters will avail itself of all of these below listed forms of distant (DX) communication:
F-layer skip every 11 years at or near the Solar peak-- along with the HF spectrum.
E-layer skip, regularly at the Spring of every year, and other times; also seen on 10 Meters
Meteor Scatter (skip) several times each and every year (at regularly noted meteor showers.
Auroral Skip, at times when major solar events ionize the D-layer of the ionosphere.
Tropospheric Ducting, at weather plus maybe E, or F layer events.
Knife Edge Refraction over mountain tops, not too great for distance, but fun!
These are the physical elements that make the Magic! You see when you have bands of frequencies that can be propagated by ducts of differential air temperature, that’s pretty magic. When you can have bands of frequencies where signal propagation can be facilitated by the exhaust gasses of jet aircraft, that’s Magic, and of course I don’t mean that in a literal sense. My point is that it is fun and interesting to exploit these methods of signal propagation, and learn about them.
The counterpoint of this is when we run into people who will tell us that this is not important, fun, or that there are only certain ways that WE MUST PROCEED in these endeavors. Noted fables that I have heard through the years are:
1) You must use horizontally polarized antennas!
2) Cubical Quads don’t work on VHF!
3) Vertical omni-directional antennas will not work on 6 Meters for DX!
4) “J” or J-pole antennas are less efficient than Ground Plane antennas!
I think that part of the fun is to de-bunk such ideas! It is also fun to learn the perspective of any amount or shred of truth that might be contained in such broad statements! Let’s take a look at each one of these; and see what might have been meant by any negative aspersion, and lets see if we can benefit from the contrasting truths.
Why must you use a horizontal antenna? This is often done so as to improve “Signal to Noise Ratio”. It is true that much, or maybe even most, electrical noise has a vertical component. This is “pulse noise” generated by ignition sparkplugs, or other arc bursts of energy. Remember though that pulse noise is the easiest sort of electrical noise to effectively cancel!
In any case, while this noise is most notable, in larger cities, where overhead power lines are prevalent, horizontal noise will be the most obvious! It will be so predominant that it will virtually make a blanket of noise at relatively high signal levels. When this S3, S4, S5 or higher noise level exists, many radio signals or VHF band openings may get lost in the noise.
I know of many practical instances over the years when I with either a vertical quarter wavelength Ground Plane, or a home-made copper “J” antenna -- both of which don’t work on 6 Meters -- was able to work either E-layer openings, Meteor Scatter, Auroral, or F-layer skip, before many ‘big gun’ horizontal Ham’s could hear the DX signals. Why was this?
A vertical antenna has a lower angle of radiation than does a horizontal antenna. That is in fact why horizontal Yagi’s etc must be raised to appropriate height to provide an optimum launch angle. Most 6 Meter Ham’s who are serious about working DX will have an antenna tower of some 60 feet or better, and one or more Yagi beam antennas of at least 1.5 wavelength booms. Or, perhaps better to say, they will try to at least provide a good 10 dBd of antenna gain. A 25-foot boom Yagi will do that, as will two 4 element Yagi’s on 12-foot booms.
So if a simple unity gain, or less than unity gain (the Ground Plane) antenna will work quite nicely for 6 Meter DX, after all, I worked 50 states and several countries with such verticals, what would be the best beam antenna configuration.
You can stack multiple beams on a tower and improve radiation angle. If you want to keep things simpler though, put two Yagi’s up vertically polarized. Two 4 element Yagi’s as I mentioned before will yield 11.2 dBd of gain. Subtract about 1 dB for transmission line loss, and you still have better than 10 dB’s at a very nice low angle of radiation. This also works with even shorter tower heights. A short tower will kill horizontal antenna performance but not when they are vertical!
How about that statement that Cubical Quads don’t work on VHF! This was said in all seriousness once at a VHF/UHF conference in the California town of Santa Maria. This conference even sponsored “an Antenna Gain Contest” on Sunday near the close of the conference. After the statement had been made, Saturday, a hasty visit to the local hardware store garnered some 12-gauge wire, some wooden furring strips, and an S-239 coax connector was obtained from somewhere.
After a few fevered hours of sawing, drilling, assembling and testing, the 4 element Quad was produced that you will see in the web posted article below. The winning entrant is that antenna that has the greatest gain, for the shortest boom length. That is the advantage of quads, they produce much higher gain, over relatively short boom lengths. They do unfortunately develop “I squared R” losses pretty quickly as well, such that after the 5th or 6th element, further gain is minimal. Yagi’s by contrast can be as long as is mechanically practical, and they will just keep developing gain!
This quad did won the contest by the way! The next best antenna a “KLM Band-pass Log Fed Yagi” produce 13 dB’s of gain but it was more than twice as long!
I have already touched on vertical Omni’s but, I thought that comment about “J” or J-pole antennas being less efficient really tossed me for a loop. A “J” antenna is simply an end-fed dipole, with a Q-line matching device. There is no more efficient matching method other than the Q-line transformer! Take a nice vertical half-wave antenna, match it to any desired impedance -- with practically no loss -- how can that be bad!
What about the other bands? I’m not so certain, as I have not had nearly as much or as broad experiences on 2 Meters, 135, 70, 33, or 23 centimeters. Experience and self-learning is key! It would be nice to find out and test these concepts however. I guess most Ham’s don’t do this because they don’t want to take a chance. I’m getting to be a little long in the tooth, with gray chin whiskers, and legs that don’t climb antenna towers as easily as I used to. I know one Ham on 135 centimeters that tries things just to find out! Now to me, that’s what Ham radio is all about!
