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Re: Pre-amp?



Hi Jim,

>I need some advise from all you digi-sat users. 

You've found the right place! No shortage of people here and 
I'm sure you'll get a range of good advice to guide you.

>I am using a Kw TS-790a to a 70cm eggbeater downlink and a 2m
>ringo ranger uplink antenna's. 

The TS-970a is a good rig from reports I have heard but my experience has
been that no matter how good the "all-sky" antennas are, you can expect only
fair results at best. (see below...pre-amps)

>The downlink antenna will be mounted on one
>end of the roof and the 2m antenna will be on the other end about 70 ft
>away.  

This is a good idea to mimimise desense of the receiver by the nearby
uplink transmission. The frequencies are not exact multiples of course
but near enough to cause de-sense if no precautions are taken. I use a 
70cm cavity filter made from copper tube. There are several designs around.
You may find the antenna separation is enough. My beams are on the same
short boom so I NEED that cavity.

>Both antenna's will have about  50 ft of coax to the rig, rg-8 to the
>2m and 9913 for the 70cm.  The question that I have is, will I need a 70cm
>preamp to get good results on the 9k6 digi-sats? 

Definitely YES! and make sure it is as close to the antenna feedpoint as you
can get it, like... attached if possible. You will hear stories of working
the satellites with a rubber-duckie and whilst this can be done sometimes it
would not be a good idea to base one's station design on this premise. The
signals from the amateur satellites are weak and you need all the help you
can get. I use high gain CP yagis and the pre-amps are still very useful.
They will be essential for any serious work using omnis.

>Which digi-sat should I start with?

KO-23, KO-25 and UO-22 all require the same ground station setup so you
might as well go for all of them. 

>Tnc is a paccom and computer is a laptop runing wisp.

I have a PacComm Tiny2 with G3RUH 9600 baud modem and I run WiSP32. You
should have no problems there.

>Later I would like to link the local terrestrial packet network, what is
required to set this up (satgate?).

What is required here is some good solid co-ordination with the "satgate"
controller. You will need to contact Andrew, G8TZJ in Lancashire, UK and
check to see if there is a need for a satgate in your area. The entire
world-wide satgate system is very closely controlled to ensure that it works
efficiently. Too many or too few satgate stations in any one area can have a
bad effect. It's not possible to just start one on your own. BTW ... it's a
very onerous task requiring a lot of effort and dedication and once set up,
a satgate station forms a critically important part of the whole network.
The co-ordinator has to be certain that a station will not 'pull-the-plug'
for any trivial reason. Such situations have occured in the past.

Good luck with your project Jim, I look forward to seeing some mail from you
on the digisats. Keep the questions coming until you get there...hi.

My best regards, Bill ... vk3jt, Milawa, Australia.

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