[R-390] zero adjust knob

[jm]

Hi Larry,

I have just repeated the test.

First I have calibrated on 700 kcs (cal position). When the knob returns to
the counter clockwise position, the signal (70db) is maintained.

Position AGC and station tuned 747 kcs. Disangaged the zero knob, maximun
reading 70 db. After that, when the knob is returned to its position, the
signal becomes weaker (50 db). The new strongest signal occurs at 746 kcs.

The second test was on 17700kcs. Calibrated at the Cal position there was
a  60db signal. Used a station in 17680 kcs. with 60 db signal too. When
returning the zero  adj knob to the position, every thing is ok this time.
The signal remains steady at 60 db.

Very strange, isn't it?

I realised that when calibrating on 700 kcs, and tuning after the station
at 747, the signal strongest point is at 748. Perhaps there is some kind of
misalignment in the 0.5-1 Mc band? It is not apparently a problem with the
clutch (?)

Many thanks for your help.

Jose
EA8DCP


El dom., 5 may. 2019 a las 5:51, Larry H (<larry41gm at gmail.com>) escribió:

> Hi Jose,  You're scenario is very perplexing.  It's not unusual for the
> 'zero adj' to change frequency as you turn it in the cal position, but not
> as you describe your problem.  I'm not sure what's going on there, but I
> can't think of why it's different in cal and agc.  Are you using cal in the
> same band as when you are using the known station?  How strong of a station
> is it?
>
> Regards, Larry
>
> Regards, Larry
>
> On Fri, May 3, 2019 at 8:10 AM jm <josemic at gmail.com> wrote:
>
>> Hi fellows
>>
>> I have an annoying problem with the zero adjust knob. When I use the
>> calibrator of the receiver things are well.
>>
>> The problem arises when I try to zero-beat using a broadcast station with
>> a
>> known frequency.
>>
>> Loose the knob, zero-beat and when I am tightening the knob I can realise
>> how the signal measured with the carrier meter begins to decline. The more
>> I tight the more the needle descends. The final result is a mismatch of
>> 1-2
>> kcs.
>>
>> It is strange for me that the problem occurs only in the AGC o MGC
>> position
>> and not with the calibrator.
>> Can you help?
>>
>> Thanks and regards
>>
>> Jose Isasa
>> EA8DCP
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