[Amps] BLF188xr amp

[Scott, Christopher]

Hi all,

First question:  when I try to subscribe to the digest, I get an "access forbidden" error message ?


But my question relates to swr mismatch protection.  My project is a 2 x Blf188XR 1200 watt amp, 80/40/20, for ssb service.  I've ordered a 4z4rb board, and got my two Fets for 129 euros each from www.pcs-electronics.com.   I spent $190 on a 0.75" x 6" x 12" copper heat spreader, and it will be mated to a large aluminum forced air heat sink.  As much as I hate to do it, it seems that soldering the fets in is best to keep case temps reasonable.  That makes one doubly worried about blowing the fets.

They brag about 65:1 swr survivability, but this is pulsed.  Clearly a post LPF reflectometer ref sample is necessary to shut it down with a poor match, say above 2:1. But I see another pitfall; the switched LPFs being set to the wrong band.

So, is the best solution adding another reflectometer after the output transformer and prior to the filter to protect against that?  With an expected third harmonic being 10-12 dB down at this point, the threshold might need to be high, like 5:1 ...

Chris Scott
W4NEQ