[Elecraft] XV-50 LNA problems

[G3VVT at aol.com]

In a message dated 31/03/05 23:06:29 GMT Daylight Time, gdaly at spiretech.com  
writes:

I'm thinking external T/R relay is the smart move. If the relay is  rigged
to rest in the transmit position, when the transverter is powered  off, the 
out
of band signal will land in the PA output, I suspect the  output of the PA
module is a big strong MOSFET or bipolar, that can take a  few volts on it's
drain (or collector) when it's biased off. When I add a  "real" amp, the plate
of an 8877 can take big voltage ;-)




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External T/R relays to isolate the unused antenna feed and dump any  unwanted 
energy into a dummy load with some form of interlock to prevent  transmission 
until the feed is enabled would be the cheapest option by far to  resolve the 
problems with damage to the XV-50 RX front end.
 
The commercial systems I worked on had ferrite isolators in the TX antenna  
feed to stop exactly what you talked about, i.e. TX power from another TX 
coming  back down the feeder into the PA as this could generate unwanted RF  
products at the PA. The ferrite isolator works as a directional coupler,  allowing 
TX power towards the antenna, but any energy coming back from the  antenna 
towards the PA from another source is dumped into a dummy load. Not  normally 
needed for ham equipment working in simplex, though essential with  systems on 
busy sites working in duplex such as repeaters. Used universally  with 
transmitter combiners into a single antenna.
 
Bob, G3VVT