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Re: [Amps] Input relay for QSK amp

To: "'Amps reflector'" <>
Subject: Re: [Amps] Input relay for QSK amp
From: "Paul Christensen" <>
Date: Sun, 9 Dec 2018 11:10:23 -0500
List-post: <>
>"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 

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 

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