Hi all,
I've noticed a similar problem at my station. The receive signal levels
will drop by tens of decibels. Sometimes I hear it happening and it takes a
couple of seconds. to drop from normal signal levels to the much reduced
levels. Sometimes it happens when I'm not listening and it just seems like
maybe I switched bands and forgot to readjust the antenna tuner. One tap of
the key and the receive signal levels are restored to normal.
It was easy for me to guess where the problem is, because it started when I
added a coaxial switch to my system. I suspected flaky contacts on the
switch and was able to confirm this by changing the switch back and forth
between positions. That restored to receive signal level just like a short
transmission did..
The switch causing the problem is a two position Daiwa switch. I have seen
and own other very similar switches with other names, such as MFJ on them.
I have also experienced similar problems with Dow Key and other coaxial
relays. Presumably a layer of metal oxide forms on the contacts, causing
high resistance in the signal path. Some small motion of the contacts or a
bit of transmit power can break through the oxide and reestablish a low
resistance connection.
Of course this could occur in relay contacts inside the radio too if it has
any. Don't look only to the radio for the problem though.
Ken N6KB
On Thu, Sep 15, 2022 at 3:00 AM Bryan Lee Cornwell via TenTec <
tentec@contesting.com> wrote:
> Hi Shawn
>
> It may be as simple as a dirty slide switch on the rear panel. It may be
> marked TRX/RX. A few drops of DeOxit may help
>
> 73
>
> Lee K2BLC
>
>
> On 9/15/2022 8:06 AM, Andrew Moore wrote:
> > Hi Shawn -
> >
> > The symptoms you describe aren't the same as what I ran into with my
> > Corsair II (jumpy VFO) but might be related. I'm almost certain the fix
> > here was exercising variable resistor R29 on the oscillator/mixer board
> > (80975). I think got crusty and oxidized over the years. It's part of a
> > bias circuit for some bands. This includes 20 meters, so again, might
> have
> > nothing to do with your issue, but it's an easy fix to try.
> >
> > Locate 10K potentiometer R29, and put two marks on it - one on the moving
> > part, one on the static part - so you can put it back where it started.
> Run
> > the pot back and forth a bunch of times and return it to the original
> > position.
> >
> > 73 de NV1B
> > ..
> >
> >
> > On Wed, Sep 14, 2022 at 10:58 PM Shawn Upton via TenTec <
> > tentec@contesting.com> wrote:
> >
> >> I do mostly 40m CW, and sometimes I have issues with RX. It will just
> >> fade away. I tap the key and it comes back. few seconds later, it
> fades
> >> away...
> >>
> >> Thing is, it will not do this cold. Sometimes it won't do this for an
> >> hour. Then do for a few minutes, then work its way out of it. Other
> times
> >> it seems to keep doing it once it starts. Sometimes it will just do it
> to
> >> annoy me... I don't work other bands all that much but I don't think it
> >> did it the other weekend on 20m, but maybe it was just in a good mood.
> I
> >> tried wiggling the band knob tonight and that did not seem to help when
> it
> >> was acting up.
> >> I haven't looked at the schematic but I'm guessing the TX/RX relay is on
> >> the way out. But wondering if anyone else has seen this and has advice.
> >> Thanks,Shawn kb1ckt
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