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RE: 1.2G Mast mounted amps



Ed,
A couple of items: I built the 25 turn Helix and would look for about
16.75db gain. I will drive with an Icom 910H through 130' of line which
gives me 2 watts at the Dog-House. I'll run that through a 3db/5watt pad to
get me to the max input of 1 watt to the PA23-50 brick. The original rating
on the brick was 50 WTPO, however they have derated it and now say 40 WTPO.
(They will likely rename it the PA23-40) That equals about 1300 Watts ERP,
RHCP. Yes, I am getting it through SSB America and I think it was about
450-475.00. I don't have the price here with me so I am just guessing.
Keep us posted!
Gunther Meisse
W8GSM
Site: www.wmfd.com/w8gsm
e-mail: gjmouse@neo.rr.com

-----Original Message-----
From: Edward R. Cole [mailto:al7eb@ptialaska.net]
Sent: Monday, September 03, 2001 7:44 PM
To: gjmouse@neo.rr.com
Subject: Re: [amsat-bb] 1.2G Mast mounted amps


Gunther,

Nice pics on the web page...someday I got to bite the bullet and put up a
web page.

I'm curious about the PA23-40 amp.  I'm not familiar with it, but sounds
like maybe it is one of the SSB units?  Tell me more and especially costs?
One of the lessons from my first attempts on mode-L and responses from the
survey is that line-loss will kill you [isn't that I didn't know this...but
I seem to have to re-learn this lesson over again].  If using <20w it is
especially important to get that power to the antenna, which means placing
it as close as possible.  It looks like a min EiRPc of 400w is needed, and
800w would be better for reliable operation in competition with mode-US
stations [EiRPc = circular polarized EiRP].

I am moving my 15w transmitting converter adjacent to the loop yagi on the
crossboom so the antenna feed will only be 6-foot of 1/2-inch line [est.
loss = 0.3 dB].  That will input 14w to the 20 dBi gain antenna for EiRP =
1400w.  But this reduces to EiRPc = 700w because of linear/circular
polarity mismatch.

I see your 25T-Helix is close to the "brick" box.  I wonder what you expect
for antenna gain?  Helix gain claims are all over the place.  I'm guessing
maybe 15-16 dBic???  If so, you are close to the polarity adjusted gain of
my loop-yagi [17 dbi].  Based on that and 2.75 times the power input,
you'll have something around a three s-unit downlink S/N...nice!

Look forward to talking on mode-L.

Ed

At 04:11 PM 9/3/2001 +0100, you wrote:
>Dave, I am housing all my bricks at the tower/antenna. I am using a home
>brew 25 turn Helix on 1.2Ghz with an Icom 910H in the shack 130 feet of
line
>and a 1watt < 40 watt brick at the tower. See:
>www.wmfd.com/w8gsm
>Good luck,
>Gunther Meisse
>W8GSM
>
>----
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