I'm asking a couple of questions for a friend for whom I've been passing
along portions of this thread to, and who is involved in getting a 80m 4sq
up and running. Test equipment is limited. He's using elevated radials - 9
per vertical- and a home brew quadrature coupler from ON4UN's book. The
verticals are nearly full size, with just a small matching network at each
base. It's working quite well but there is concern about some of the
problems with feedline interaction that this thread has been talking about
recently.
Specifically, how are the vertical radiators isolated from the 1/4 wave 75
ohm feeders? There isn't enough spare coax to wind a choke. Buried 3/4 wave
feeders and a coax choke? How many turns is "enough" for 80? Ferrite
beads? If so what mix and quantity is needed?
The main feedline back to the station is about 230 feet long and buried,
varying from a few inches to a few feet. We suspect a coaxial choke wouldn't
hurt but is it needed with the assumed choking action from the buried
length?
Another friend wanted me ask about using stainless .035 mig wire for
radials. It has a rather high resistance, measuring about 10 ohms for a 1/4
80m radial length. I say that's WAY too high and he needs to forget about
using it. However he'd like a 2nd opinion.....
73 Don
VE6JY
>
> > Did you know that you lose field strength with elevated systems if you
> don't use a choke or current balun to
> > isolate the system from earth? I don't see many people isolate feedlines
> from the feedpoint of small radial
> > systems, yet it can be as much as a dB or so change!
>
> Somehow I confused the feed lines (plural) statement with the impedance
> transformer/phasing lines that feed each element. I do have current
baluns
> at the feed point to the Comtek phasing boxes, which does as you say.
>
> > Like the comments before none of this says "don't use them".
> > It just points out the quirks of using a sparse radial system of any
type
> and things you have to watch for.
>
> > If you look at:
> > http://www.w8ji.com/verticals_and_baluns.htm and
> http://www.w8ji.com/end-fed_vertical_j-pole_and_horizontal_zepp.htm
> > you'll see how important it is to isolate feedlines even on
groundplanes
> with four radials.
>
> I use baluns on all of my antennas - just because. I think the balun
gives
> me a more symetrical radiation pattern.
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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