[amsat-bb] Re: need plans for 70 cm preamp

G0MRF@aol.com G0MRF at aol.com
Tue Feb 26 00:27:28 PST 2008

In a message dated 26/02/2008 03:39:11 GMT Standard Time, rlasso at zianet.com  

Need  recommendations for plans for an easily constructed homebrew 70cm 
mast  mount preamp with built in RF sense TR switch (VOX controlled). I 
will not  be running more than 50 watts in New Mexico or possibly 100 
watts in CA  when I move there.
thanks and 73, Robert W6RQR

That's really tough Robert.  Unless there is some sequencing going on  inside 
your radio then any RF sensing circuit will mean that the relay contacts  
will be hot switched on transmit.
A couple of seriesed limiting PIN diodes may help, but with 100W across  them 
for a few 10s of milliseconds even that may not be enough to protect the  
On the preamp side, the design that was published in the journal in August  
(2006?)  works well and has a noise figure of 0.5dB and is a no tune  design.  
Details are on  g0mrf.freeserve.co.uk


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