[Amps] Input relay for QSK amp

[Paul Christensen]

>"Jim, You're right in principle, of course. The problem is that a well-designed amplifier relay circuit shouldn't depend on what transceiver is used. The amplifier itself should be immune to hot-switching in all situations."

Just my opinion, but I think any well-designed amplifier T/R circuit must sample input RF, then decide whether or not to switch in/out relays.  Some transmitters apply RF either before, or simultaneously with the amp key line.  Many Alpha amplifiers -- and I suspect other late-model commercial amps do sense RF before engaging or disengaging the RF relays.  So, to W8ZR's point, it's more than just ensuring the amp's in/out relays are fast. 

My homebrew 8877 amp uses the S-QSK board that appeared in the 2014 ARRL Handbook. The board incudes footprints for either Arduino Nano or PIC microprocessors.  It can be used in many different RF switching applications, but works especially well for amplifier T/R switching.  Timing changes are all done in software; the hardware remains the same.  An on-board BNC connector is used for RF sensing to less than 100 mW.  I also designed a tiny board as an option for remote RF sensing.   

My amp uses two LEDs to sense pre and post switching failure.  When that occurs, the LEDs remain pulsed for about a half-second.  This is a good indicator that hot-switching *could* have occurred, but didn’t because of S-QSK's RF sensing.  If the LEDs flash, it's time to start looking at the rig's RF and key line timing.  This method does the same as scope monitoring, but without the scope.

Paul, W9AC