[R-390] Receiver Overload?

[Bill Smith]

Good question, James.

I get about 30 on the Carrier Meter, but apparently lower on the lower
bands.  I will have to check the calibrator - it is underneath, so I haven't
done much with it.  I recall tweaking it, perhaps I had better look at it
more carefully.   I had dismissed it because it looks like it is coupled to
the receiver with only a 2pf capacitor.  But I suppose even a component of
that sort can go bad.   Possibly there is something strange going on with
the multivibrator circuit too.   At any rate, can't do it tonight, will have
to tackle it in the future.

I agree the receiver is operating as if one tube is running wide open.  But
I have checked the tubes in the RF section - I used an RF choke in series
with the VTVM DC probe to look at AGC voltages at the 1st and 2nd RF stages.
All is well, and looked at the AVC voltage on the antenna trimmer; good
there also.  I have checked through the IF circuitry and can't find anything
to complain about there, either.

I would think, though, that if the problem was AVC, that backing down the RF
control would improve the overload/intermod (don't know yet which it is).
But backing down the RF control, while reducing the sensitivity of the
receiver, does not affect the noise.   Interesting, though, switching the
Function switch to CAL does reduce the noise and allows the station to be
heard.   Of course that is likely because the input relay has disconnected
the antenna when the Function switch is in the CAL position.

By the way, there is still signal leakage through relay K101 when it is
activated by switching the Function switch to CAL.  Pulling the unbalanced
input (although nothing is connected to it) reduces the signal as shown on
the Carrier meter, but does not silence the receiver.  Pulling either one of
the balanced antenna BNC connectors (J110 or J111)  does remove the signal.
Will have to look into that also, although that could simply be a factor of
a ground loop between the back panel and the balancing capacitors in T201,
T202, ect.  (Gads, those caps are a bad idea!)

Anyway, thanks for the suggestion, and will keep looking.  Might be
interesting to pull the BNC out of the calibrator and see what happens.

73 de Bill, AB6MT
billsmith@ispwest.com


----- Original Message -----
From: "James Miller" <JamesMiller20@worldnet.att.net>
To: "Bill Smith" <billsmith@ispwest.com>
Sent: Friday, March 08, 2002 7:58 PM
Subject: Re: [R-390] Receiver Overload?


> Just out of curiosity, what does your CAL signal read on the meter?  It
> averages around 40 dB on mine, slightly higher on lower bands.  If
> you're getting an 80 dB broadcast station, and the CAL signal is still
> around 40, then you must live next door to the station!  Also, are you
> sure you are getting AGC to the RF amp tube, AGC from the IF module is
> making it to the RF module and the grids?  It acts like your RF module ,
> or one of the RF amp tubes, isn't getting AGC to keep its gain down.
>
> Bill Smith wrote:
> >
> > Yes,  AB6MT :-)    I do have a 160 meter dipole antenna, and this has
always
> > been a good radio location.  It might also be interesting to hook up the
> > spectrum analyzer in Communications Monitor to the antenna and see if I
can
> > determine just how much energy is out there, and where.
> >
> > But that doesn't (yet) explain the receiver's operation.  Think the next
> > step is to hook up a 'scope and a signal generator and see what I can
> > reproduce.
> >
> > ----- Original Message -----
> > From: "James Miller" <JamesMiller20@worldnet.att.net>
> > To: "Bill Smith" <billsmith@ispwest.com>
> >
> > > Are you real close to a high power AM station?  Could be that.
> >
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