[R-390] Staggertuned IF Question

[Mark Huss]

As I was taught (1975) at Devens (ASA), you tune using the Visual 
Alignment and stagger tune flat on 16 kHz bandwidth. As an aside, it was 
mentioned that if you ran across an IF deck with a filter cover with no 
dimple, tune that one straght. No mention of replacing the IF Deck with 
the newer ones. Making it meet spec was a big deal, since you did not 
know where it might be four years down the road. For 'Hogs' and 'RATT's' 
( Morse Code Intercept and Radio Teletype) you could get a better noise 
floor by straght tuning them, and we did that on special order, and made 
a notation with grease pencil on the IF Deck's filter cover.
R-390's and R-725's required sweep alignment for best operation. Never 
bothered to do the three-point alignment on them (mostly R-725s). 
Besides, the point on them was to get flat phase shift through the IF 
deck, with bandwidth being secondary. They were used for doppler DF, and 
phase shift could throw them off a few degrees, as well as widen the 
propeller, making direction more ambigous.

Flowertime01 at wmconnect.com wrote:

> seem to remember that the first run of R-390A (the ones WITHOUT the 
>trimmers on the top of the mechanical IF Filters. The Mechanical filter 
>cover does not have a dimple at the mounting screw) was straght tuned. 
>When Collins did the mod to add the trimmers, they also changed the 
>circuits on the IF Transformers to stagger-tune them. At least that is 
>what I remember from the R-390A classes.
>
>---------------------------
>Mark,
>
>I think you are right on the Collins Radios.
>
>Then later non Collins manufactures went back to the straight 455 tuned IF 
>strips.
>The transformer and cap values in the cans were changed to get enough 
>bandwidth and can so that a straight tune was wider than the mechanical filters.
>
>As most of the receivers were not Collins receivers most of the R390/A are 
>straight tuned.
>
>We tuned every thing straight. Remember I was tuning for a bunch of CW 
>operators and they could have cared less about any thing more than 2K wide.
>
>If you are trying to tune the IF for some good Short Wave AM reception, then 
>getting the sweep generator out and doing the adjustment with a visual pattern 
>on the scope is the way to go.
>
>Try stagger tuning your IF deck and it will not take you long to determine if 
>it is a stagger tuned deck or not. 
>
>More bandwidth is more fidelity. It is also more noise in the band pass. If 
>you are doing DX SW a narrow bandpass may still be a better option. You can get 
>a lot more fidelity by recapping the AF deck up to a good 16KHz audio than 
>you realize by opening up the IF bandpass. Until you get the Audio deck to 
>respond to 16KHz there is little point in trying to tune an IF deck out to that 
>response width.
>
>Roger. AI4NI
>
>
>
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