[ARC5] More BC-455 IF thoughts

[Roy Morgan]

Stagger tuning:

During and after WW-2, the development of radar systems brought considerable attention to IF amplifiers. Often working at 30 Mc, these amplifiers needed relatively wide bandwidths, considerable gain, and very importantly, low or at least very constant phase shift across the band pass region. The received returning radar pulses had to be amplified in high fidelity. 

The MIT Radiation Laboratory, “Radlab” published their famous series of books including “Vacuum Tube Amplifiers” by Valley and Wallman. (Volume 18 ??), one section of which deals with the design and implementation of this sort of amplifier. 

As I remember it, some important design factors are:
-stage gain
-number of stages
-tuned circuit Q
-stage center frequency 

Stage gain and Q is set to calculated values by resistances at each tuned circuit. Center frequencies are chosen to result in overall desired bandwidth. Flatness of phase within the bandpass is part of the calculations. 

The Valley and Wallman book is out there in “the web”.  Therein you will encounter math that not many of us can understand easily, if at all. 

A published modification to the R-390/URR (“non-A”) IF strip was to clip out the Q-setting resistors in the IF cans. Although the radio was then “much hotter”, the desirable bandpass characteristics were destroyed. 

Roy sends.

> 
> -----Original Message-----
> From: J Mcvey via ARC5 <arc5 at mailman. 
...
> Subject: Re: [ARC5] More BC-455 IF thoughts
> 
> Traditionally, yes, the term 'stagger tuning' refers to widening.  That is accomplished by having the peaks at the high and low of the BW freqs, ...
> 
> On Friday, April 13, 2018, 10:40:33 PM EDT, Bill Cromwell <wrcromwell at gmail.com> wrote:
> 
> Stagger tuning is used to increase bandwidth - just the opposite of narrowing it. 
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