[amsat-bb] Preamp mounting?

Greg D. ko6th_greg at hotmail.com
Sat Apr 17 17:42:55 PDT 2010

Hi folks,

So, a follow-up to my previous message.  All this discussion about EME got me thinking...  We're always taught to put your preamp as close to the feed point as possible, but as with everything, there are tradeoffs.  Where should the Preamp be mounted?  


1 - on the antenna boom, at the feed point (or attached to the CP relay)

2 - on the rotor cross arm

3 - below the rotor, where the flex transitions to the main feed

I'm thinking that #1 is a problem.  Yes, it's the shortest run, but you've got the weight of the preamp
at the far end of the antenna, unbalancing things.  Depending on the antenna, it might be right in the middle of a bunch of elements, so putting a metal box there might upset the antenna's performance or impedance.   It's would also be subjected
to the strong RF fields of the antenna during transmit.

#2 is probably the best; fairly short coax run on the antenna side, and somewhat outside of the RF field.

#3 (what I have) is most convenient, and has one less set of connectors to go bad, and one less wire to snake around the rotor.  Weather proofing is easier when the object being proofed can't move, and mounting the preamp on the tower, for me at least, is a lot easier.  And, it's not THAT much more coax to the antenna.


Greg  KO6TH

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