[R-390] Coil forms and more

[blw]

A HSN states that the greatest width you can get from the R-390A is 100 kHz.
I'm pretty sure that is the limitation. I can't check my issues right now.
There is an inherent limitation in the SB-620 with the 455 kHz IF, but I
forget what it is at this moment. I think it is 1 mHz. Still useful in
crowded situations, beacon DXing, and looking for clandestines that jump
around to avoid jamming, etc.


Barry


> John,
> The SB-620 has a mixer in it. (now set for a 3395kc input) I was trying to
> find the frequency of the oscillator Heath used to mix 455kc. to the 350kc.
> IF of the SB-620.
> 
> My "guess" was confirmed, it is 805kc.
> 
> Certainly, another solution is an external mixer for 455kc. to 3395kc.
> 
> I plan to use it with a 75S-3B.  Actually my R-390A had a "panadapter"
> output on it.  A 6BE6 used instead of the 6C4 in the third mixer.
> I removed it last winter in a general maintenance session.
> 
> Jim
> 
>> Hi Jim,
>> if I read your post correctly you are attempting to mix down 455 kc to
> your
>> Scanalyzer IF for use with a 390 rx. Cool!
>> 
>> In this case you want to use a low-side LO injection frequency, because if
>> you use a high-side LO you will end up with a spectral inversion which
> will
>> be very evident on your Scanalyser display!
>> 
>> The unwanted mixer products should be far enough way because with the 390
>> you'll only be able to see a narrow slice of the band anyway:
>> - if you are monitoring the IF output then the scanned bandwidth will be
> the
>> 390 IF bandwidth
>> - if you are tapping off the 3d mixer (recommended) the bandwidth will be
>> only 35 to 40 kc max due to all
>> the cascaded selectivity in the RF and 2nd IF stages (yes, it is that
>> narrow).
>> 
>> Also, try to use a balanced or double balanced mixer, you'll get far less
>> troublesome RF and especially LO feedthrough into your scanalyzer IF.
>> 
>> John
>> KA1XC
>> 
>>> Thanks to all for the suggestion and help with my SB-620.  After many
>> years
>>> the 455 kc. conversion project might get off the ground.
>>> 
>>> Does anyone know the mixer oscillator injection frequency?  It is not
>>> stipulated in the manual or on-line sources.
>>> 
>>> Here is my guess:
>>> The IF of the Heath "Scanalyzer" is 350kc.
>>> To convert 455kc., the oscillator may be either 805 or 105kc.
>>> The "high" injection of 805kc produces first order products of 350 and
>>> 1260kc.
>>> "low injection of 105kc produces 350 and 560kc.
>>> 
>>> The "High" injection products are further apart and it would be easier
> to
>>> filter the unwanted sum frequency.
>>> So my "guess" is 805kc.
>>> I know the value of the parallel capacitance.  If the oscillator
> frequency
>>> is known, I can calculate the coil inductance.
>>> 
>>> Any help or ideas greatly appreciated.
>>> 
>>> Jim