[Hallicrafters] s-76

[mac]

For a given circuit Q, the bandpass of a resonant circuit is a fixed  
percentage of the resonate frequency.  Thus, a lower frequency circuit  
will provide a narrower bandpass than a higher frequency circuit .   
For example - 5% of 500KHz = 25 KHz vs. 5% of 50 KHz = 2.5 KHz.  Not  
quite that simple in practice, of course but that's the principal of  
the thing.

As to why the popularity of 50 KHz, I suspect this was because this  
was the frequency of the IF in the BC-453 command receiver widely used  
as an outboard selective IF in the 50's (and up to this day).

Dennis D. W7QHO
Glendale, CA



On Mar 12, 2010, at 9:08 AM, Julian Bunn wrote:

> Thanks Grant: interesting! Could you or someone explain the technical
> reason for choosing this low frequency
> in the 2nd. IF?
>
> Julian
>
> Grant Youngman wrote:
>>> However, I have had some trouble aligning the S76 ... if I remember
>>> correctly the first IF is at 50kHz, much lower than the usual  
>>> 455kHz.
>>> I'm curious to know why this frequency was chosen?
>>