[R-390] Alignment questions

[Bob Camp]

Hi

Since the crystals in the crystal deck can not be tuned you pretty  
much have to put up with what ever you have or swap them out. Back in  
the days when the radio was new getting crystals for them was fairly  
easy. Today it's not quite as simple.

More or less:

1) Run through the range of the radio and figure out the highest and  
lowest band in terms of frequency error. Hopefully this will be a few  
hundred cycles and not a few KHz.

2) The PTO runs through a slip drive to correct for the error. The  
idea is to center up the PTO between the high and low band with extra  
room on each end.

3) You slip the drive on the counter to get everything to center up  
once you have range for the high and low bands.

The net result is that the PTO is running at who knows what frequency  
most of the time. It will be within a few hundred cycles most of the  
time.

The Y2K manual is probably the best thing to refer to when the manual  
you have does not make sense. On page 6-20 it talks about the  
alignment procedure for the first variable IF using the generator at  
18.25 MHz and the radio at 7.200 and 7.250 MHz.

     Enjoy!

         Bob Camp
         KB8TQ



On May 7, 2005, at 7:08 PM, Barry wrote:

> I've started aligning my "new" R390A.  When I got to the point of  
> being able
> to hear AM broadcast stations, I used my frequency counter, tuned  
> the PTO to
> the desired frequency (3.455 - 0.770) for a strong local station on  
> 770kc
> and set the BFO to 455kc.  At this point, the heterodyne theoretically
> should have been zero; however, I was hearing a very high-pitched
> heterodyne.
>
> Investigating this, I found the 17mc oscillator is 16.997mc.  This  
> (along
> with any inacurracy in the second crystal oscillator frequency) is  
> the cause
> of the non-zero beat.
>
> When I originally set the PTO, I tuned it to 3.455 (by frequency  
> counter),
> set the counter to x.000 and clamped it together.  If the other  
> oscillators
> are dead-on, this would be valid; however that's not the case.
>
> My first question is this: Using one of the crystal deck  
> frequencies that is
> the closest, should the PTO be set to accomodate the off-frequency  
> of the
> 17mc oscillator?  In other words, it won't always track between  
> 3.455 and
> 2.455 exactly.  To do this, I can loosen the clamp from the Oldham  
> coupler
> to the front-panel shaft, dial in a known frequency (say my 770kc  
> station),
> set the BFO to 455kc, and while holding the dial at 0.770kc, rotate  
> the PTO
> shaft to zero-beat and retighten the clamp.  Is this a good method?
>
> One more question:  For aligning the second IF, the manual states  
> to set the
> signal generator to 18.750mc and the R390A to 7.250mc.  I think  
> this should
> either be 18.250 & 7.250 or 18.750 & 7.750.  Is this a known issue  
> with the
> documentation?  If so, which frequency is correct?
>
> Thanks for reading!
>
> Barry - N4BUQ
>
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