Last winter, I bought an ARR mast-mount GaSFet preamp for 6m. It has now failed
for the
fourth time, and I'm about to give up on it. Each time, ARR has repaired it
under warranty.
Several times I described to them the proximity of the 6m antenna to other
antennas and
asked what signal levels it should be able to take. The "data sheet" and manual
don't say.
Finally I got a response that it is rated for 10 mW at its input, which works
out to 700 mV in
50 ohms.
In my installation, the preamp is at the radio (for obvious reasons, I haven't
trusted it
enough to stick it up in the air) there's a 6m ICE BPF filter between the
preamp and the
antenna, and I'm driving it with an ICOM 746, letting the preamp detect RF for
T-R
switching. The 6m antenna is a pair of PAR loops that are a few feet from a
pair of 2m
PAR loops, also getting 100 w. I've measured the attenuation of the ICE filter
at >60 dB at
2 meters (on the bench with a 50 ohm load and good test gear). It's also >45 dB
on 10
meters, >55 dB on 15 meters, and > 60 dB below 10 MHz, so it ought to be
protecting
against any stuff from my HF antennas, the closest of which is an 80/40 dipole
that is
about 15 ft away. 60 dB of attenuation would take 700 volts down to 700 mV, so
it doesn't
seem reasonable that the preamp should be blowing up.
There is also a Polyphaser in line with the antenna, and there have been no
lightning
storms that are likely to have done the damage. The most recent failure
happened in the
middle of a 6m QSO during the last VHF contest.
So the question is, is this a common problem? Am I doing anything wrong? Could
I do
anything better?
Jim Brown K9YC
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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