[ARC5] Re-reading Gordon White article...L-2 in a 'command' receiver

[Mike Morrow]

Robert wrote:

> The paragraph you quoted this time from one of the BC-348 manuals
> describes the same apparent results but in a different manner than
> the similar paragraph from the ARA/ATA manual.  As the BC-348 is a
> multiband set with a low IF frequency relative to the bands covered
> (plus has a fifth band lower than the IF), A.R.C.'s fix probably
> wouldn't work.  So RCA used a tuning capacitor driven resistor.
> Plus the description in the BC-348 manual is probably incorrect in
> calling it "internal receiver noise".  The noise performance of the
> tubes used in the early version BC-348's is not bad over the
> frequency range that they cover.  Note that the BC-342 and the
> Hammarlund Super Pro's of the same vintage plus a dozen different
> Navy shipboard receivers, all using similar tubes, don't mention
> this as a problem.  And they didn't use similar antennas.
>
> I'm going to stick by my guns.

and

> Given that most operation of the BC-348 would have probably been
> below 10 MC, and certainly below 12, as that's the upper limit
> of the BC-375, the two manuals are referring to the same operating
> frequencies.  I can't think of any characteristics of the tubes
> used that would account for any increase in either sensitivity or
> noise.  I suspect that the noise reference has to be to more 
> apparent output noise due to increased gain or increased signal
> levels at the antenna terminals.  The tubes used aren't noticably
> noisy at those frequencies.
>
> The only other possibility I can think of would be if the impedance
> of the RF tuned circuits increased significantly from bottom to top
> of each band or in each ARA.  But absent evidence to the contrary,
> I'm inclined to stick with the antenna theory.

I think you make very valid points.  I too found the "internal noise"
explanation questionable.  I do suspect that the ARA process and the
BC-348 process for reducing sensitivity on any particular range of
frequency coverage as frequency was increased were dealing with the
same issue, whatever its source.

(Robert gave me permission to post the above off-list discussion
 we had on this topic.)

Mike / KK5F