In a message dated 96-09-17 10:09:30 EDT, you write:
>
>Anyone have any experience using or modeling a shunt fed vertical
>with elevated radials? Without isolation at the base of the
>vertical, it seems doubtful the impedance of the elevated radials
>would be low enough to help much, but I'm not sure.
>--
>Scott K9MA
Hi Scott, This question has been "bugging" me for years now. I have
attempted to measure a system here, and I have measurements made at a
broadcast station (made by other people) showing elevated radials, at least
in these two cases, do not live up to claims. They are about 4 dB or more off
from predictuions.
There is also data that shows NEC fails to model a low dipole accurately so
far as ground loss is concerened, in that case a low dipole modeled by NEC-2
shows about 4 or 5 dB more signal in the model than the real world.
My Beverages also measure more current taper than NEC models, indicating
losses would be higher than predicted.
I'd like to see more real A-B field strength tests, hang the impedances!
I also have an open question about radiation. If anyone knows the answer, I'd
appreciate a direct E-mail.
If I have a wire one hundred feet long and ten feet off the ground, and it
carries one ampere of current at the feedpoint and over a thousand volts at
the open end, how do I keep that wire from coupling to the ground by electric
and magnetic fields, as well as radiation fields?
The only way I know of to cancel those effects are by having a wire with
equal and opposite distribution right next to the original wire (in that case
it's a transmission line instead of a radial). The only way I know of to
reduce that effect is by spreading the current out over more wires, reducing
the nearfield electric field and magnetic fields and radiation fields from
the wire by reducing the voltage and current in the wire.
What magic is at work in elevated radials that allows the fields to just stop
below the wires, and why wouldn't it show up in direct measurements of fields
near the ground below and between the wires?
73 Tom
>From k1jks@juno.com (William G Bithell) Tue Sep 17 18:29:46 1996
From: k1jks@juno.com (William G Bithell) (William G Bithell)
Subject: WAE Last Two
References:
<c=US%a=_%p=comcastpc%l=NEGRIL-960915222107Z-211@negril.comcastpc.com>
Message-ID: <19960917.171749.5495.7.K1JKS@juno.com>
You're right! Lotsa "Last Two" call letters.
It's not so bad in the CW contests.
:)
73, Bill K1JKS
>From leduc@atla3.agfa.com (Dave LeDuc) Tue Sep 17 18:40:14 1996
From: leduc@atla3.agfa.com (Dave LeDuc) (Dave LeDuc)
Subject: using .wav files for voice keying
Message-ID: <9609171740.AA28080@chip.agfa.com>
Is anyone using ".wav" files for digital voice keying.
I think it would be fairly simple to match the output of a PC sound card
to the microphone input of the transmitter and write an interface to play
the file. I'm sure someone must be using this approach however I havn't
seen anything in any of the major journals.
Dave K1EPJ
>From kb2hun@wizvax.net (William R Liporace) Tue Sep 17 19:32:40 1996
From: kb2hun@wizvax.net (William R Liporace) (William R Liporace)
Subject: using .wav files for voice keying
Message-ID: <Pine.LNX.3.91.960917143027.7883A-100000@wizvax.wizvax.net>
HI Dave and to all:
Voice Blaster from LTA Industries does just that. It is a TSR program
that will interface with CT/NA and possibly TR-log. Kits are available
for the keying and interfacing the radio/computer.
GL CUL Will
William Liporace KB2HUN kb2hun@wizvax.net
763 Huntingdon Drive KB2HUN @ K2TR (yccc packet cluster)
Niskayuna, NY 12309 KB2HUN @ WA2PVV (NEDA)
518-346-3804 home 518-471-2837 work
>From zettel@homer.libby.org (Steve Zettel) Tue Sep 17 20:08:59 1996
From: zettel@homer.libby.org (Steve Zettel) (Steve Zettel)
Subject: 40M Yagi comparisons
Message-ID: <v03007802ae649e82cf9c@[199.172.3.217]>
Here I go to the well, again.
I've done my basic homework: studyied the ARRL Antenna Book, read the
Antenna Compendiums, borrowed Jasik, Johnson, and Kraus from the library.
I have Leeson and Lawson on my bookshelf, somewhat dog-eared by now. K6STI
is loaded on my computer, and W7EL is soon to join him. . . . I've read and
archived and re-read the cq-contest reflector archives and visited KA9FOX
many times. No hyperspace link has gone untravelled. . . . I sleep with the
collect back issues of NCJ under my pillow, CQ Contest Magazine has the
place of honor in the reading rack beside the commode. . .
Yet, one mystery remains.
Why does every contesting ham in the known universe use a Cushcraft 40-2CD
40M Yagi?
Alright, so I exaggerate. Some hams use Telrex quasi-military monsters or
build their own full-sze 300# gorillas. The poor, but hard-working amateurs
have carefully crafted and meticulously pruned 40M wires up in the trees. .
. . The masochistic evidently use KLM's, delighting in the spectacular view
from the tops of their towers as they annually rebuild reflectors and
directors. . . .
So I solicit your collective wisdom and experience for input and enlightenment:
Have you had any experience with commercial 40M Yagis besides the
Cushcraft? It certainly seems to be the standard, and strengthened a la
W6QHS, is reputed to be a durable antenna. How DOES it stack up,
performance-wise? I understand from anecdotal testimony that the KLM 40M
Yagis are not robust and often require major seasonal maintenance. Hygain
has the Discovery 7-1 (dipole), 7-2 (2el), and 7-3 (3el) 40M antennas in
their literature, but I have never heard of any amateur using one, nor read
any independent reports about their performance or reliability. Given
Hygain's reputation and track record with their other antennas this seems
very unusual to me; does it have some dark, secret weakness? I am seeing
some accounts of the Force 12 monoband 40M Yagis; they would seem
attractive because of their weight and wind load, if they have the long
term reliability and if their b/w and gain claims are not (perish the
thought!) out of line with physical realities. How about other
manufacturers?
I am looking for a reasonable-size/weight 40M Yagi to put on a mast with
either a TH7 or a KT34XA at the top of my (soon to be completed) 45G tower.
. . . Yeah, I'd like to build one like the Europeans, with a Rohn 25G boom
and full-size 4" irrigation pipe for elements and a tractor motor to turn
it, but not in THIS lifetime. . . .
You may reply direct and I will summarize for the reflector if there is
enough interest.
Thanks and 73,
Steve Zettel KJ7CH kj7ch@libby.org
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