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I plan on installing a vertical antenna soon. I expect it to cover from 80 meters to 10 (or perhaps 6). I plan on putting down 32 radials.

I am wondering if 16 66' and 16 33' radials will be just as efficient for the higher bands as would having fewer radials separately cut for each band of interest. (Eg. 8 radials each for 80, 40, 20 & 10.)

The same question differently: If I cut all the radials for 80 meters, would it negatively affect the signals of 40, 20, 10, etc.?

Does anyone know the answer to this or where I can find it?

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    $\begingroup$ What type of vertical antenna, Marq? Is it designed to be a multiband antenna or is it just a single mast or wire with no traps, etc.? $\endgroup$ Commented Sep 23, 2018 at 17:15
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    $\begingroup$ In addition to Mike's questions - elevated radials? If so, height? $\endgroup$
    – Glenn W9IQ
    Commented Sep 23, 2018 at 17:32
  • $\begingroup$ These radials will not be elevated. They will be on the ground. Regarding the antenna, I am leaning toward either the Hustler 6BTV which has band traps or the Jetstream JTV 680 which I understand to be just aluminum tubes clamped together. $\endgroup$
    – MarqTwine
    Commented Sep 24, 2018 at 22:07
  • $\begingroup$ Phil gave you a very good answer. This page may also be of use to you. $\endgroup$ Commented Sep 24, 2018 at 23:12

1 Answer 1

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Rule of thumb: if the radials are elevated, at least two resonant radials for each band.

If the radials are buried or lying on the surface, at least 16 radials, each at least a 1/4 wavelength at the lowest operating frequency, and don't worry about resonance: just get as much wire in the ground as you can. More and/or longer is better.

The objective of any radial system is to avoid current in the soil by presenting a lower impedance alternative. Current in soil is undesirable since it dissipates power in ohmic losses, reducing antenna efficiency.

In an elevated radial system, the separation between the radials and the soil surface provides isolation, meaning the current in each is largely independent. The soil and radials could be considered two parallel current paths, as such the one with the lowest impedance will take most of the current. Thus, it's important to minimize the radial impedance by ensuring some radials are resonant on any band used.

In a buried radial system, soil and radials are tightly coupled due to their proximity. Low ground losses are achieved not by providing a low impedance alternative but rather by effectively increasing soil conductivity by stuffing it full of copper. Thus, attempting to reduce radial impedance by cutting some of the radials to be shorter to be resonant on higher frequencies is futile or even counterproductive.

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  • $\begingroup$ Are you saying that if I put 30 radials down for 80 meters, that it won't negatively affect the higher frequencies? $\endgroup$
    – MarqTwine
    Commented Sep 24, 2018 at 22:16
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    $\begingroup$ @MarqTwine Yes, that's what I'm saying. Your objective is to approximate an infinite, lossless conductive plane. Being an infinite theoretical object, it isn't "for" any band. Just say down as much copper as you can. $\endgroup$ Commented Sep 24, 2018 at 22:25
  • $\begingroup$ Phil W8II posted Answer 1 originally, but his comments were lost during my addition/edit of them today. Hopefully a moderator can fix that, or, if Phil has a record of those original comments and PMs them to me, I will return them to his Answer 1. $\endgroup$ Commented Jan 7, 2020 at 10:03
  • $\begingroup$ @RichardFry I think your edits changed too much to be acceptable as an edit. Generally I try to limit edits to fixing obvious errors (like a missing "not" or a math error), broken links, correcting spelling, improving formatting, maybe correcting grammar when the author is not a native speaker. Anything more substantial can be suggested in comments, or you can always add an additional answer. $\endgroup$ Commented Jan 8, 2020 at 16:40

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