[MRCA] ARC-5/SCR-274-N IF Coil Mod

[B. Smith]

When I checked my Command Set IF coils on a HBR receiver I built  on an 
actual 80 meter frequency , I got a 3.4 Kc value. See plotted graph. 
When I actually swept the IF's   it  was slightly better.  (each 
vertical div is 5 db.)  IF Coils were  were as far apart as the notches 
would allow.  Sorry about the lousy scope picture.  Also note that the 
peak is around 86.2 Kcs which was the best response curve when 
adjustments were made.   You should not have any loss when switching 
from close spacing to far spacing. Don't know much about the S markings. 
Those IF coils were pretty good to be designed and manufactured overnight.
Z






On 3/6/2014 12:15 PM, D. Platt wrote:
> Gentlemen,
>
> I've just completed the preliminaries of modifying a set of BC-454-A 
> IF coils to try and enhance selectivity.  With some very basic 
> information, I have successfully moved the two coils apart about 
> 1/2".  There was some trial and error in doing the first one, but I 
> have found a fairly easy way to accomplish the deed. Having now done 
> so, and making a comparison of the two sets of coils, I find that 
> selectivity has improved by reducing the measured bandwidth about 2 
> kHz at the 6db points.  I do find, however, that some additional 
> external AF gain was required as the losses in loose-coupling the IF 
> coils has reduced overall throughput amplitude.  Has anyone else done 
> the above and what were your results?  Also, the coils are marked with 
> the "S" (stabilized) mark, as were other components in this junker set 
> (made available courtesy of W3PWW, Ted).  What, in reality, did the 
> "S" modification intend to do?  I sure can't readily see any component 
> differences??
>
> Thanks
>
> Jeep - K3HVG
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