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RE: Thanks for Coax advice. What about preamps?



> -----Original Message-----
> From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
> Behalf Of Robert Rice
> Sent: Sunday, October 17, 1999 2:19 AM
> To: amsat-bb@AMSAT.Org
> Subject: Re: [amsat-bb] Thanks for Coax advice. What about preamps?
>
>
> Thanks all for the thoughts on coax. I still have to work out
> exactly where I am going to mount my satellite antennas and
> from there will give additional thought to what kind of coax..

There are several schools of thought on this.  I am in the process of
mounting EVERYTHING up on the tower.  My thought is that a 100+
watt amp into a 15dB antenna with only 1 dB of loss between will
give the best possible efficiency.  I hope to use the coax loss from
the shack to the tower to provide just enough loss so that the amps
get maximum drive from the transceiver without overdriving, and then
adjust the pre-amps to make up for that loss.  I have a 160 watt
Mirage 144 MHz amp already.  I am still considering a 100 watt Mirage
for 432, or a 160 watt model, the manufacturer's name eludes me
this morning.  100 watts at 15 dB is over 3000 watts ERP, and that
should be enough.  On the other hand, the 160 watt amp would give
me more allowance for additional losses.  The final factor may just be
that a 100 watt Mirage is easily found used, but the 160 watt unit
is new.  Gotta look at the finances this fall.


> Clearly I need to work out a mounting arrangement that
> will involve the shortest practical coax run.

I use a Glen Martin Engineering roof-top tower, on the roof right
above the shack.  That keeps all of the lines short.  The H.F.-beam
is farther away, and the low-freq dipole is the farthest.  This is
the optimum set-up for frequency Vs loss.  I got the 936, and it is
quite strong enough for my needs.  Here is the URL.

http://www.glenmartin.com/


> Everyone sings the praises of mast mounted pre-amps.

And well they should, they can make the difference between a Q-5
contact completed or a series of QRZs until frustration sets in.


> Can anyone offer a clueless newbie some sage advice on
> preamps.  What do folks recommend.  Good manufacturers?
> Models to avoid?

I got a great deal over the net on the SSB electronics 2000 and
7000 models.  I have used the Icom units, and I can say without
any reservations that the SSB units are better.  Again, any unit
is better than none at all, but good ones are preferred.  Since the
SSB units are adjustable, you do not lose any dynamic range in
your transceiver from over-driving the front end.  The SSB Elec.
URL is:

http://www.ssbusa.com/



> Are you better off to run a separate power line or does powering it
> up the coax work?

I am currently powering mine through the coax.  I (at this time) have
no experience doing it the other way, so I cannot comment.  I will be
powering them from a direct source once the roof-top system is
complete.  I am not sure, but I expect that there will be little difference.


>
> Robert Rice
> WB5PKN
>


Hope it helps, but then again, I do not have thousands of contacts
on satellite, so I am not a pro either.  Good luck.



Vy73,  Mike.   KD9KC    MARS: AAV6EV
kd9kc@elp.rr.com  -  kd9kc@amsat.org
Home page: http://www.qsl.net/kd9kc/
The farthest WEST ham in West Texas.

An armed society is a polite society.

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