[TowerTalk] ARR Preamp Failures

[W0UN -- John Brosnahan]

At 08:33 AM 10/5/2004, Jim Forsyth wrote:
>I don't know which model you have but I looked on their web site and they
>have 25 watt models and 160 watt models. Took me about 30 seconds to find
>that out.

You are right, Jim (AF6O)!    K9YC mentioned that he was using it in the
shack--but when I reread his note he mentions he has not mounted it on his
mast yet--which would imply that he actually purchased a mast-mounted
preamp.  Since K9YC never mentioned which model he is using, I don't know
what the relevant specs are.

So I owe K9YC an apology--ASSUMING he is using the 160 watt model.

On the other hand my original statement IS true.  RF switched preamps
are PRONE to this type of problem by their very nature.  The sensitive
FET gets clobbered with RF for as long as it takes the preamp switch circuitry
to detect the RF and actuate the relay.  Which also would seem to imply
that the radio is hot switched into the antenna.  Meaning there is no load
on the radio for some number of milli-seconds.

One wonders if the extra 1 to 3 dB of feedline loss might help play a role
in keeping the RF voltage from getting too extreme under the switching
transients.

And K9YC never mentioned the actual failure mechanism.  I ASSUME that
the FET died, but it might have been something else like the relay or
the detection circuitry.  But with a number of failures it is clear that the
system is not functioning correctly.  And whether that is due to a problem
with this particular preamp, or with the preamp design in general, or with
a system problem in the shack is not yet determined.

In any case it is not REALLY a topic for Towertalk--especially in view
of Steve's recent reigning in of the off-topic messages.

73--John   W0UN