Hi Jim and gang,
I use protection diodes on the front end of my W1FB preamps (as well as
before an IC amp in the preamp, and on the output of the preamp) and have
never been able to detect receiver performance degradation on 160 meters
due to the clamping diodes (had to include the diode clamps before the IC
amp in the W1FB preamp to prevent continuous failures of this IC when
transmitting). On the rare occasion (only happens during a contest) when
I've heard what sounds like ever so slight intermod I switch to my TX
vertical for RX and the odd phenomena has always still been present so I've
never been able to find fault with my added diode protection system.
I have half size pennants feeding my preamp and they have an approximate
gain of -46 dbi, and suspect this is the key to my success with diodes as
clamps (very low input levels from my RX antennas). Therefore I certainly
don't agree with avoiding diode clamps 100% of the time, as I believe they
should be considered on a case by case basis depending on the gain of your
RX antenna, etc.
I also have W7IUV preamps and don't use diode clamps with them at all since
their front ends appear bullet proof based on the transistor used.
P.S. I only run 100 watts output, but my TX vertical is within 30 or 40
feet of my RX pennants.
73,
Don (wd8dsb)
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