[amsat-bb] Preamps and Polarization Switches

Edward R Cole kl7uw at acsalaska.net
Sat Jul 2 15:16:49 UTC 2016


Good comments from both Bob-WB4SON and Jim-KQ6EA.

I might add that starting simple is a good approach as you will learn 
the effect that each improvement makes as you go.  But saying that, 
if you can afford simple preamps like the ARR P144VDG and P432VDG 
($79/ea.) and add a coax TR relay ahead of them it will work as well 
as more expensive switched preamps (depending on cost of relays).  If 
you are only running up to 50w relays can be cheap (check e-bay, Fair 
Radio, Nebraska Surplus Sales).  I would not trust a  diplexer to 
have sufficient isolation to protect preamps.

I am re-installing my satellite antenna system and using this type of 
system for modes UV & VU.  I have an equipment box for the preamps 
and switches mounted just below the Yaesu B5400 az-el rotator so only 
antenna cables run to antennas; I do have separate Rx and Tx coax 
lines to my equipment (which require modification to break out the Rx 
separate from Tx connector).

Using a switched preamp avoids the extra coax lines and mods so 
probably easier to implement with most radios.  I have one mounted on 
another 2m antenna where I run 150w, but run a separate dc keying 
line and do not utilized the internal RF switching detector.  This 
avoids hot switching the preamp.  I am involved in eme so have a 
station sequencer to control TR switching in my station.  This 
considered a "frill" for most satellite stations.

I decided to go simple with a M2 2M7 linear antenna and using part of 
my original M2 436CP42 (RHCP only - not switched).  I'm installing 26 
elements of that antenna.  If I later feel need for CP on 144 then I 
may add 7 elements to the 2M7 and add RHCP phasing cable (again no 
switch).  I have not found need for filters using high gain yagis for 
desense.  Radio is old but good FT-736R running 30w barefoot.

I have equipment for 1268 and 2401 MHz but not installed for the 
present (used for AO-10/AO-40).  I have an 8-dBic patch antenna for 
2400 mounted but not connected.  I have old preamp and drake 
converters for that band (stored).

73, Ed - KL7UW
     "Kits made by KL7UW"
Dubus Mag business:
     dubususa at gmail.com

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