This is a very common problem with T/R relays.
The high power (current) of "transmit" is more than
enough to overcome, albeit temporarily, this bad
contact syndrome. The tiny receive signals cannot
penetrate the layer of oxidation that has formed. So
you will see no symptoms in transmit, but when you
switch to receive, the contacts "wipe" and generally
the receive signals start off OK, but fade (sometimes
rather quickly).
If you do a quick "key" of the radio (blip the PTT)
again you wipe the contacts and temporarily clean
them.
If you choose to physically clean the contacts, don't
use anything abrasive (no files, sandpaper, etc). The
ultrathin plating will disappear in a heartbeat and
then the oxidation problem will be worse. A strip of
paper (brown grocery bag material is good since it is
fairly rough) soaked in a contact cleaner, dragged
between the closed contacts seems to be enough to help
in many cases. (I've had luck with it anyway).
If you can get a new relay, that's probably the better
solution.
Mike N2MG
--- "Dennis L. Wade" <dwade@pacbell.net> wrote:
> Hello,
>
> After almost 15 years, I've dragged out my gear
> from storage to get
> back on the air. Recently, I've erected an antenna
> and hooked
> everything up, so there is no real "it worked fine
> yesterday" frame of
> reference.
>
> The problem I noticed was that sometimes, but
> not all, on returning
> to receive from transmit, the signal levels would be
> considerably down
> from their "normal" levels. This low receive
> condition would persist
> for a long time, only occasionally returning to
> normal levels. After
> some investigation, I've concluded that the TR relay
> is probably at
> fault with fouled contacts. What threw me was the
> lack of symptoms on
> transmit: I thought I'd see erratic SWR and or
> power out indications,
> but apparently the problem is limited to the receive
> side. Only the one
> contact is dirty? I'll have to open it up and see.
> Any one else have a
> similar problem? Any other likely suspects?
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