[TenTec] Argonaut II/Delta II crystal filters

[Dr. Gerald N. Johnson]

On Wed, 2007-08-01 at 11:14 +0100, Bob Towers wrote:
> I'm not exactly happy with the Jones filter on my Argonaut II.
> 
> a) the centre of the bandpass shifts up frequency (on USB) when I 
> tighten the bandpass width
> 
> b) the narrowest width setting is about 700Hz: I could do with 500Hz or 
> narrower.
> 
> The manual warns against adjusting the two sets of 4-pole filters unless 
> you have a network (spectrum, surely?) analyzer, which I do. Anyway, the 
> adjustment pots are all locked in position with some sort of fixative.

Network analyzer is a spectrum analyzer with signal source to measure
the pass band characteristics. It could probably be done with a noise
source and the spectrum analyzer or manually using a signal generator
and detector, though that might be slow to get the necessary detail.
> 
> Has anyone had a go at adjusting the filters?
> 
> If so, I would appreciate some advice - which might be, of course, don't 
> try and fix it!
> 
> 73
> 
> Bob
> MM0RKT

I'd be inclined to go with an external DSP audio filter if the inherent
selectivity wasn't quite narrow enough. But I tend to prefer wider
rather than narrower so I can tell what's going on around the QSO I'm
copying.

73, Jerry, K0CQ