A friend's coax-fed G5RV worked ok with his 990 (built-in matching unit).
No external "tuner" needed. It worked all bands 160 to 10m: on 160 I made
him a simple switch to short the coax and tune/match against ground. His
needs were modest - no dx, just local chit chat. It was sensitive to coax
length and I coiled up the first 10ft or so at the junction to the ladder
line. He replaced it with an expensive Carolina Windom which worked just as
well but not as reliable.
David
G3UNA
----- Original Message -----
From: "Brett gazdzinski" <[EMAIL PROTECTED]>
To: "'Elecraft'" <[email protected]>
Sent: Thursday, May 17, 2007 1:27 PM
Subject: RE: [Elecraft] OT - G5RV antenna & baluns
What many do is put up as much wire as possible, then
take the feedline down to a remote balanced tuner in a dog house,
then run coax or hardline to the shack.
That is the best setup for high power AM multi band work
I suspect.
Running AM, you have to derate everything like baluns and traps
to 1/4 power or less.
I once had a B+W folded all band dipole rated at 1.5kw that
B+W told me was only good for about 150 watts of AM!
I used to have resonant 80 and 40 meter dipoles, but the 80
meter one was directly over the house lengthwise and
got into everything. When the coax went bad, I took it and the 40
meter dipole down and put up various antenna's, and the best working
thing I can fit was the home made G5RV.
On high power, it works on 80 and 40 meters without anything getting
hot (coax, tuner), and works great on 40, on 80 I have to watch
the power as the tuner arcs on the upper frequencies.
That took some experimenting with lengths to move the high
voltage point away from the tuner some.
There are lots more choices when running ssb or cw, traps,
baluns, and auto antenna tuners can all handle those modes.
Not sure about the digital stuff, but part of the AM problem
is the very high short duration peaks that can sneak past
any limiting, 3 or 4 kw in my case, which can be very high voltage
at a high swr.
The big advantage of the G5RV is that if done right, the swr
is not real horrible on most bands, and loss is not real high
in the coax if its short.
A good trap dipole might be better if you run lower power,
but the G5RV has nothing to wear out or get water/bugs into,
is light and easy to put up, and easy to make.
Brett
N2DTS
> I have G5RV's original article introducing the antenna.
> He specifically states that it is a 20M antenna, and yet it's
> now somehow become a do-all-bands wonder ... an almost
> "cult" thing.
In all the G5RV articles I've read, including the original,
it's a multiband
antenna. It was specifically designed that way by G5RV.
What's special about the G5RV is that if it is properly built
and installed,
it will present a low (but not 1:1) SWR and good efficiency
on the non-WARC
bands.
And it's simple.
> The same thing happened with the single-wire fed
> Windom years ago. EVERYONE had them.
>
That antenna goes back to the 1920s. The "Windoms" we have
today are really
off-center-fed (OCF) dipoles.
> Why would one want to clobber up an open-wire fed dipole?
> The G5RV version requires a tuner when used on bands other
> than 20M, so why not bring the open-wire to the tuner and
> dispense with the open-wire-to-coax transition kludge hanging
> outside in the sky? It's a simple application made difficult.
No, it isn't.
The reason for the popularity of G5RVs and OCFs is this:
Properly made and installed, they are capable of low SWR (not
unity) on
multiple bands, and they wind up with a coax feeder of random
length coming into
the shack.
While a tuner may be needed to get 1:1 SWR at the rig, the
tuner need not be
balanced, nor does it need to have a wide matching range. A
simple, low cost
tuner can do the job of tuning out the relatively-small mismatch.
OTOH, if you simply put up the classic
dipole-fed-with-ladder-line and don't
concern yourself too much with lengths of dipole and feeder,
the result can be
a wide range of impedances at the shack end of the line. So
you need a much
more expensive tuner to get the system to work efficiently.
All three systems will work well if done right. After all,
they're all just
dipoles with different feed systems. The question is, what
resources are
available?
73 de Jim, N2EY
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