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brightsparkey · 22nd Jun 2018, 10:55 am

Thank-you once again for a most illuminating discussion.

I've always hankered after my own copy of Zverev, but I've used it mostly for the low pass prototypes - never really paid the k-Q tables much attention - I see now that they were for this sort of design problem.

So sumarising:

- the coupled resonators have low coupling coefficient - i guess I wasn't expecting as little as 10% (is that k=0.1 for mutual coupling coefficient?). When they say 'critical coupling' in the tuning instructions, they mean for minimum bump in the middle.

- in terms of shape of IF filtering - is it fair to say that the filters in a domestic radio (i'm thinking more of '50s and '60s sets here) are Q limited and so there is no benefit in trying to produce a particular overall shape, hence the tendency for each stage to be synchronously tuned?

-coupling controls - fascinating to have a mechanical cam for shifting the windings! so the winding spacing is derived by trial and error resulting in the spacing between the two coils. Presumably there are rules of thumb for the dimensions of the windings and former - looks like the link to RDH has some of these. More study required..

In the SABA IF transformers - there seems to be a core for adjusting the coupling - is this an intermediate winding for coupling and the core used to adjust the coupling factor?

As an aside - I'm very grateful that people here feel able to spend their time discussing these subjects - I'm a practicing analogue/RF engineer and I'm finding that fewer people even in my own discipline have good analogue skills - the art of such techniques needs to be preserved so that others may 'stand on the shoulders of giants'. I'm also grateful to learn new things and it brings much satisfaction to get to grips with things and to appreciate the cunning of our forebears.

Kevin.

22nd Jun 2018, 10:55 am	#23
brightsparkey Pentode Join Date: Sep 2017 Location: Cambridge, Cambridgeshire, UK. Posts: 148	Re: How do IF transformers work? Thank-you once again for a most illuminating discussion. I've always hankered after my own copy of Zverev, but I've used it mostly for the low pass prototypes - never really paid the k-Q tables much attention - I see now that they were for this sort of design problem. So sumarising: - the coupled resonators have low coupling coefficient - i guess I wasn't expecting as little as 10% (is that k=0.1 for mutual coupling coefficient?). When they say 'critical coupling' in the tuning instructions, they mean for minimum bump in the middle. - in terms of shape of IF filtering - is it fair to say that the filters in a domestic radio (i'm thinking more of '50s and '60s sets here) are Q limited and so there is no benefit in trying to produce a particular overall shape, hence the tendency for each stage to be synchronously tuned? -coupling controls - fascinating to have a mechanical cam for shifting the windings! so the winding spacing is derived by trial and error resulting in the spacing between the two coils. Presumably there are rules of thumb for the dimensions of the windings and former - looks like the link to RDH has some of these. More study required.. In the SABA IF transformers - there seems to be a core for adjusting the coupling - is this an intermediate winding for coupling and the core used to adjust the coupling factor? As an aside - I'm very grateful that people here feel able to spend their time discussing these subjects - I'm a practicing analogue/RF engineer and I'm finding that fewer people even in my own discipline have good analogue skills - the art of such techniques needs to be preserved so that others may 'stand on the shoulders of giants'. I'm also grateful to learn new things and it brings much satisfaction to get to grips with things and to appreciate the cunning of our forebears. Kevin.