Jon,
Just to set the record straight, the R7 is a 3/8 Wavelength design (versus
the 3/16 WL you gave).
73,
Joe, W1JR
At 01:23 PM 3/7/2002 -0500, W4ZW wrote:
>Remember that the two most common "verticals", the R-7 series by
>Cushcraft and the DX-77 by Hy-gain are not 1/4 wave verticals. The R-7 is
>a 3/16 wl vertical and the DX-77 is a hybrid windom fed 1/2 wave vertical.
>
>I've found that both antennas work better if they are elevated to minimize
>ground losses. I have found the R-7 and DX-77 to be excellent performers
>when elevated at least 1/4 wl above ground, or even better 1/2 wave above
>ground on their lowest cut frequency. That's about 66' or 1 full wl on
>20M. I read W4RNL's piece to say that the radials made a difference of
>less than 1Db over poor ground diminishing as the existing ground improved
>(less lossy). Note that this observation was for vertical dipoles that
>were virtually ground mounted. Dipoles should exhibit less ground loss
>than verticals since they are electrically and physically complete.
>
>Both the R-7 and the DX-77 use a counterpoise to minimize ground losses,
>not eliminate them. I would love to see a direct comparison of these
>"radial free" verticals and a true dipole vertical. The Force 12 ZR-3 is
>a short vertical dipole that uses linear loading by means of rings to
>achieve electrical and physical length. Even as short as it is, I would
>not be surprised to see it perform better than a ground mounted
>"radial-free" vertical.
>
>I have done rather extensive on-the-air comparisons of the R-7 and the
>DX-77 as compared to a tribander and a dipole, but the antennas were all
>mounted above 150' in one test and above 240' in the other so they won't
>track most installations. I did find that the vertical often gave me
>better DX take-offs than the dipole and on some occasions better than the
>tribanders. I expect that was due mostly to polarization. I, for one,
>think they are pretty good antennas for what they are. Simple to install
>and small real estate requirements providing you can get them up at least
>33' in the air which is about 1/2 wl on 20M. A push-up mast works pretty
>well. Automatic band switching for seven bands in a compact package makes
>an attractive package for the real estate challenged. I even installed a
>R-7 on a 10' mast on the roof of my house in a deed restricted community
>rigged with a gate hinge and pulleys. I made a small saddle for the
>antenna to lie in while horizontal to protect the upper capacity hat. At
>night I simply pulled my line and I was on the air. It even worked while
>horizontal with my FT-1000D's built-in tuner. My neighbors believed it
>was an elaborate lightening system.
>
>Now that I have no restrictions, I'm back to yagis and wire arrays, but I
>still keep one R-7 or DX-77 up as an alternate antenna.
>
>
>Jon Hamlet, W4ZW
>Casey Key Island, Florida
>
>"A little bit of paradise in the Gulf of Mexico"
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