Ron,
I've modeled my antennas using EZNEC. What I've found is that the
horizontal pattern is more sensitive to conductor length on dipoles.
Electrical height determines vertical angle of arrival. For NVIS work on
40 30' high is good; double that for 80. However,as you get higher than
1/4 wave the lobes start to lay down. there is an exception to this and
that is a null that is created at the horizon that can occur when you
get to certain heights between 1-2 wavelengths above ground. It's part
of an interference pattern.
The Carolina Windoms are really interesting affairs. they are
designed to have radiation from a part of the feed near the dipole. I've
chosen to use an18' radiation length on my 66 footer. This allows a
little better radiation at the horizon on the lower frequencies with a
small impact on ten. However, at 22' things got crazy, so, 18' became
the magic number.
Using these configurations for a fair number of years I find that
this seems to work. I do reach out and touch people when band conditions
are in good shape, and in the present iteration, the antenna is at about
40' on one end and about 30 feet on the other. This is not by design but
rather by aim and the slope of the ground. I do run both QRP, ~5 Watts
and QRO, 100 Watts.
What I do and what I say about antennas are NOT absolute. These are
good guides that can be tailored for specific locations. The only
important thing to remember, IMHO, is antenna tuners take care of many
bad estimates and low loss feed lines mask many mistakes.
73,
Barry
K3NDM
On 2/14/2013 1:29 AM, Ron D'Eau Claire wrote:
If you like to use it for chasing DX on 10 meters, you'll get better results
with a slightly shorter radiator - something about 42 feet overall. That's
because a longer antenna generates a big lobe pointing straight up on 10
meters - not very helpful for DX-ing on that band. At 42 feet the main
lobes are still down near the horizon on 10 meters.
At 42 feet, the efficiency is excellent down as low as 40 meters.
73, Ron AC7AC
-----Original Message-----
From: elecraft-boun...@mailman.qth.net
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of k3...@comcast.net
Sent: Wednesday, February 13, 2013 5:37 PM
To: Ken G Kopp
Cc: elecraft@mailman.qth.net
Subject: Re: [Elecraft] OT: G5RV's and variants
>From my experience, hams misunderstand antennas more than anything else
they have as a part of their station. What I've been able to discover for
the popularity of the G5RV is that you have an "all band antenna" in just
102'. The other issues have to do with the concept of resonance in an
antenna system and the need for it.
I guess I'm just not smart enough to worry about all of the issues. My
approach has been to just hang up 132' or 66' of wire fed in the center with
open wire to a 4:1 balun near the house. My transition into the house is
either something like LMR-240 or LMR-400 to my tuner. I can use this
configuration either 80-10 or 40-10. Resonance? I really don't worry about
it too much as my tuner can address the issue for me thereby making my
transmitter happy. I don't worry about losses either. With low loss feeds,
there is little loss, even at 10 meters, with SWRs as high as 10:1.
Simplicity is key here.
The antenna that I now have up is roughly equivalent to a 40 meter Carolina
Windom, modified. My thinking on this gets a little convoluted, but it
works. For a new installation with the room, I would suggest the center fed
dipole with low loss feeds into a good tuner. And, oh yes, get it up as high
as possible.
73,
Barry
K3NDM
----- Original Message -----
From: "Ken G Kopp" <kengk...@gmail.com>
To: elecraft@mailman.qth.net
Sent: Wednesday, February 13, 2013 6:06:25 PM
Subject: [Elecraft] OT: G5RV's and variants
It's already been pointed out that the original article by G5RV indicated
that the antenna was for 20M only.
I have the original article in my files.
I've always wondered why builders of the antenna simply don't make an
open-wire fed Zepp and stop there.
Why add a "magic" length of coax ... without any kind of impedance matching
... to what would otherwise be a Zepp? Yes, the length of the coax portion
of the feeder acts as an impedance transformer ... on 20M.
On other bands, all bets are off. (:-)
The antenna requires an antenna tuner to operate on bands other than 20M.
Many tuners contain a balun so one has the option of either coax or balanced
line feeders. Why not avoid the coax-to-balanced line splice with it's
almost certain mismatch losses and connect the balanced line portion of the
G5RV's feeder directly to the tuner? If the tuner as no internal balun, one
can be made or purchased.
I once knew a local who actually coiled the coax portion of his G5RV's feed
"system" behind his desk and then connected it to his tuner. The end of the
balanced portion was within inches of his tuner's balanced line connections.
The G5RV certainly qualifies as a "cult" antenna.
73!
Ken Kopp - K0PP
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