[Central-Electronics] 600L Helicopter Parent SWR Trip

[Christopher Bowne]

Hello from Chris in Stonington CT.  I subscribed to the list several months ago, just found a digest sent a few days ago, was in my spam bucket.  Hopefully I will get more now.  

I have been running a 20A with a 600L that I acquired from George W1LSB a few months ago.  Works great overall, but the high SWR protection trips way to often on 80/75 meters, even when transmitting into a Bird dummy load with essentially flat SWR.  My coax fed inverted vee with ferrite bead common mode isolation beads at the feed point has a nominal SWR of less than 1.2 to 1 on 75/80.  I have the sensitivity pot of the SWR trip circuit sent to minimum sensitivity.  Looking at the circuit, I am thinking of either adding more resistance in series with the signal coming off the SWR bridge to the grid of the 12AT7 relay control tube, or swamping down the grid a bit.  Any other suggestions? The amp came with a melamine wedge to lock the relay in the normal position to prevent tripping, but I don’t want to go that route, and don’t think further reduction of the small SWR present with an antenna tuner makes sense and not likely to work

Chris AJ1G
Stonington CT

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