Mark,
This sounds very much like a problem that I had a year or so ago with my
K2/100 #3255 on 40m the band I had been using most of the time. The
receiver's sensitivity would occasionally drop when returning to receive
from transmit, and sometimes the audio from one or more of the SW BC
stations near 6MHz and/or 7.1 + Mhz would appear at lowish level. I
suspected that the problem might be caused by dirty contacts in one or more
of the relays used to select the 40m bandpass filters or Low Pass filters,
and it turned out that the contacts of K1 (Bandpass) were the ones. Since
these contacts only handle low level signals at lowish impedance, a little
'dirt' resistance could have a noticeable effect. I think, and this is a
guess, that the effect during transmit might not be of consequence.
To 'cure' my 40m problem, I modified only the 40m bandpass filter relay
circuits (K1a and K1b) so that about 1mA DC would be switched by the relays
along with signal, i.e. the contacts became 'DC wetted' for cleaning. This
is normal practice in such circuits. In the K2 it must be done in such a way
that does not affect the diode switches. The problem was cured for a while.
BUT, a year or so on the problem has returned, affecting 40m, 15m and 10m,
perhaps other bands, and it would seem that the KAT100 is now also involved
because sometimes simply changing the Power setting from 100w to less than
10w and back up again, restores order, i.e. when the KAT100's K1 and K2 are
worked. Although my K2/100 and KAT100 are opened up, the beasts take their
time to go into a fault condition - so the time taken to effect a total cure
might be long. As far as I can tell all relay coils etc are driven properly
at the right time. I am
also attempting to take a good look at the performance of all diode RF
switches, and whether or not part of the ongoing problem lies there, or in
their control circuits, or in both.
Because the voice comms. audio appears in your case, I suggest that a
change in propagation conditions is not a cause.
For what it is worth, and good luck.
73,
Geoff
GM4ESD
Mark Saunders, KJ7BS wrote on November 20, 2005, at 05:51 AM
>I was just working an Argentina station on 30 meters on 10.11865 (RST 549)
> and he just disappeared. I listened to him work 2 other USA stations FB
> before me. I lost him right after our RST exchanges. Now I hear very
> weak
> voice communications on this frequency, can't tell what mode.
>
>
>
> Mark Saunders, KJ7BS
>
> Glendale, AZ
>
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