In practice, I have followed the recommended practice of cutting radials for Vertical antennas to a quarter wavelength of the antenna. However, in searching through Chapter 3, The Effects of Ground, of the ARRL Antenna Book, 21st Edition, I can't find any reference to resonant radials.
In fact, in reading Chapter 3, it shows that the more radials - the better, and the longer the better - up to a certain point of diminishing returns. And, if there isn't room for long radials, then the deficiency can be made up by increasing the number of short radials to decrease the resistance of the signal return path.
I haven't found any articles that point out the advantages of a resonant ground vs: non-resonant ground. Yet most Vertical antenna articles specify Resonant Radials. Is there a different or improved radiated patern, or SWR or Impedance by using resonant radials? Can someone point me in the right direction?
If you can elevate the radials then 4 resonant radials will do the work of 120 buried radials. The radials need not run in a straight line although doing so will give a slightly better efficiency. A while back tests were run on the AM broadcast band (experiments were made from 600 kHz to 1500 kHz) and 4 radials elevated 6 feet above ground performed pretty much the same as 120 buried radials. A height of 6 feet at 500 kHz equates to about 1 foot on the 80 meter band. Therefore, even a radial at 12 inches above ground will work fine for the amateur radio bands.
I have elevated radials on both my vertical antennas. Now the radials do not run in straight lines. The radials run along my wood stockade fence, around the slab of my house, and around the retaining wall to my swimming pool. Although they start at the base of the ground mounted verticals they spread out to between about a foot above ground to almost 6 feet above ground.
Before my swimming pool was installed I had 48 buried radials "under" my HyGain HyTower. The antenna worked well. However, when the swimming pool was installed most of the buried radials were "dug up" and I had to do something else. At that time I installed 4 each radials for 80 meters, 40 meter, and 4 "random length". The performance of the vertical increased dramatically.
For elevated radials you do need to make them a full quarter-wave length long and NOT the 95 percent length that is generally used for radiating elements (this figure accounts for the "end effect" of the wire). As such, you need to use the formula 246/F (where F is in MHz) instead of the "normal" formula of 234/F that is used for the length of the radiating element.
There's an excellent article just this month is QEX that has empirical testing of various radial combinations including elevated and ground level and various numbers.
It's part of an ongoing series on vertical antenna operation, and well worth your reading.
In practice, I have followed the recommended practice of cutting radials for Vertical antennas to a quarter wavelength of the antenna. However, in searching through Chapter 3, The Effects of Ground, of the ARRL Antenna Book, 21st Edition, I can't find any reference to resonant radials.
In fact, in reading Chapter 3, it shows that the more radials - the better, and the longer the better - up to a certain point of diminishing returns. And, if there isn't room for long radials, then the deficiency can be made up by increasing the number of short radials to decrease the resistance of the signal return path.
I haven't found any articles that point out the advantages of a resonant ground vs: non-resonant ground. Yet most Vertical antenna articles specify Resonant Radials. Is there a different or improved radiated patern, or SWR or Impedance by using resonant radials? Can someone point me in the right direction?
Thanks,
Pierce W4ZDI
ON4UN's Low Band DXing has a lot more detailed information on resonant radials. It is far more meaningful to have resonant radials if you have FEW of them, and they're elevated.
But you have to be careful....technically, it's the SYSTEM that's resonant....or not. A radial is not going to be resonant by itself. (Nor is a quarter wave vertical!) What resonating (or, occasionally, LOADING) radials does for you is to scoot the current distribution around to where it's going to do you more good. Resonating radials does NOTHING to reduce ground loss...that has to be done with MORE radials, or a higher elevation.
Eric
__________________
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Steve, the N6LF study was interesting. Though it wasn't stated, the reader has to assume that all radials in all the measurements undertaken were resonant except for the case where non-resonant radials were compared a few tenth of an inch above the ground. Thank you for sending that link. One thing really stood out to me: the change of antenna current vs: distance from center. Strange..
Eric, I'm trying to find a local copy of ON4UN's book. I'm also subscribing to QEX today. Thanks KG6WOU.
Glen, I wonder if you can quote the source of your last paragraph? As I said in my query, I'm trying to find any articles that take an opposite viewpoint as that of the ARRL Antenna Handbook in regards to Vertical antenna radials.
Pierce,
Look at this article.
HF tests by Al Christman – KB8I; “Elevated Vertical Antenna Systems,” QST, August 1988, p 35
I think it also appears in the ARRL antenna Compendium Volume 5.
73,
Evan
Evan, thanks for that reference. Interesting reading. I see now that even the ARRL Antenna Handbook took different sides in different years, stating in one that resonant radials were required, then in another issue, stating that resonant radials were not required.
Nevertheless, the authors of the articles pointed out by you guys have given me a completely different outlook on setting up the counterpoise for a vertical. I learned a lot.
Evan, thanks for that reference. Interesting reading. I see now that even the ARRL Antenna Handbook took different sides in different years, stating in one that resonant radials were required, then in another issue, stating that resonant radials were not required.
Nevertheless, the authors of the articles pointed out by you guys have given me a completely different outlook on setting up the counterpoise for a vertical. I learned a lot.
Thanks to all,
Pierce W4ZDI
This is my opinion, if the radials are buried then there needs to be many of them, as in up to 120 for a commercial AM radio station. If the radials are up off the ground then 2-4 of them are enough.
This is my opinion, if the radials are buried then there needs to be many of them, as in up to 120 for a commercial AM radio station. If the radials are up off the ground then 2-4 of them are enough.
Yes, and the articles that were referenced in the previous post made it quite clear, as did the ARRL Antenna Handbook. 21st edition Chapter 3.
I was interested in finding the source of information that so many articles on Vertical Antennas have relied on when calling for resonant radials in the construction of the antenna. I've come to the conclusion that they're just not well informed.
I'm in the final stages of tuning a 16.5ft aluminum tubing vertical mounted on the roof crest of my rear storage room at about 15ft above ground level with three random length, 120 degree spaced radials. The first adjustment easily brought the SWR down to less than 1:1.5 with an R=45 and X=3. I have to pick up some small wood screw hooks today to use for keeping the radial end points firmly attached to the roof shingles/plywood underneath. Once that's done, the final adjustments should bring the SWR down further.
We appreciate your support.
Vertical Antenna Quarter Wavelength Radials
Linear Mode
