[NLRS] 10 GHz Preamp Switching

[W0ZQ at aol.com]

In a message dated 3/15/2009 9:10:34 A.M.  Central Daylight Time, 
acepilot at bloomer.net writes:
Thinking about adding a  receive preamp for my DEMI 10 GHz transverter.  
Question:  Is  there enough isolation provided by the supplied SMA T/R 
relay such that the  2W transmit amp will not destroy the preamp or 
alternatively, would it be  better to remove DC power from the preamp 
during TX?



Hi  Scott, I defer to others with more experience in this area, but here are 
some  thoughts.

1.  Would a preamp help ?   Only if the noise  figure of the preamp is better 
than the noise figure of the current front end  and/or if you need more gain 
(perhaps due to feedline loss).  One test ....  with your system warmed up, 
turn up the volume and listen to the hiss, then aim  the dish into the trees or 
ground, then aim it up into the sky (but not the  sun).  On my system, without 
a preamp, I can just tell the difference ...  the cold sky produces slightly 
less "hiss" then does the warm trees &  ground.  In this situation, a pre amp 
will not add any value as all my Q's  are aiming on the horizon (at those warm 
trees, etc).  If I was doing  moonbouce, a preamp may help.  Preamps add 
complexity, something that is  bad for rovers !

2.  I do believe that your SMA relay should provide  enough isolation IF you 
are using sequencing.  Somewhere around 1 to 2  watts, you need to start to 
use good sequencing.  What is the upper limit  ... perhaps someone else can 
comment on that, but I suspect that its upwards of  20 to 30 watts (again, 
assuming that you have good sequencing).

73,  Jon.
W0ZQ  

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