W6PQL has built a 1KW 160-6m amp using the same FET's.
He has directional couplers in front of the LPF to protect against
stupid ham syndrome and one behind to provide SWR and power out readings
for his meters.
http://www.w6pql.com/1_kw_sspa_for_1_8-54_mhz.htm
On 10/13/2015 12:31 PM, Scott, Christopher wrote:
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
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R. Kevin Stover
AC0H
ARRL
FISTS #11993
SKCC #215
NAQCC #3441
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