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Re: Thanks for Coax advice. What about preamps?



I strongly agree that the SSB amps are good, if not the best.  Spend the extra
bucks to get the 2000/7000; the helical filters do well to keep down the out of
band junk.

One suggestion:   Several friends have had problems with their preamps becoming
dummy loads on the transmit side.  I believe it's due to relay problems from RF
switching.  I manually switch mine using the PTT line and a control circuit;
sending up separate power.  Have NOT had the problems.  Even the guys who do
have the problem are able to transmit with no loss by turning the preamp off.

Good luck!
73, Jim
wb4gcs@amsat.org


"Michael P. Olbrisch" wrote:

> > -----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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