[R-390] IF Alignment in the R390/URR

[Bob Camp]

Hi

If the crystal filter is “way off” you can try to fiddle the circuit around it or you can try to replace it. Neither one sounds like a really good idea. 

If you get way far away from 455 KHz, the rest of the IF system may or may not move “far enough”. A few hundred Hz is no big deal (as mentioned in other posts). If you start talking about a KHz … that probably will be an issue. 

Do you listen to CW with the signal at 455 and the BFO at 455? Nope. You get no beat note. Is your radio likely accurate tuning wise to 100 Hz? I know none of mine are. Again, as mentioned before, you probably can live with a crystal filter that does not quite line up.

Lots of choices and lots of variables.

Bob

> On Oct 21, 2024, at 8:56 AM, Barry <n4buq at knology.net> wrote:
> 
> Larry, Jim,
> 
> Thank you for the explanation regarding the crystal filter.  I didn't realize that was the dominating part of the circuitry for that.  It makes sense to me now.
> 
> Thanks again,
> Barry - N4BUQ
> 
> ----- Original Message -----
>> From: "Barry Scott" <72volkswagon at gmail.com>
>> To: "R-390 Mailing List" <r-390 at mailman.qth.net>
>> Sent: Sunday, October 20, 2024 7:08:48 PM
>> Subject: [R-390] IF Alignment in the R390/URR
> 
>> The IF alignment instructions for the R390/URR (and, and I recall, the
>> R390A/URR as well ) begin by adjusting the signal generator to the
>> frequency that provides the highest voltage on the DIODE LOAD.
>> Apparently, this is not always 455.000kc but I'm not sure I follow why
>> it isn't.
>> 
>> When I read this, I made a possibly false assumption that having a
>> signal generator with a precision readout or an accurate counter
>> wasn't usually available and adjusting for the "best" frequency was
>> the best approach.  When I aligned mine, I chose to use 455.000kc but
>> now I'm wondering if that was a mistake.  The primary reason I did
>> that was so that the BFO could be a zero-beat when it was also at
>> 455.000kc.  That may really be irrelevant but it was my reason.
>> 
>> I started looking at the STAGE GAIN procedures and when I injected the
>> signal into the 6th IF amp's grid, I could tell that 455.000kc wasn't
>> getting me the peak on the DIODE LOAD and, instead tha frequency is a
>> few kc away from there so something isn't right about my setup;
>> however, I'm still puzzled at why the IF chain can't be "forced" to be
>> peaked right on 455kc.  Is this because there are some fixed values in
>> the transformers and a "best" frequency is the best one can do with
>> those fixed values? If not, then would someone please explain this to
>> me as I'm still not making sense of it.
>> 
>> Thanks,
>> Barry - N4BUQ
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