diy IF transformers: first attempt.

[Amie]

Thanks for the comments Trevor, but I think I'm by far a net consumer of knowledge! It may be all very well knowing theory (or thinking so),  but here's where I come to quietly read up on some of the techniques of how to actually do stuff.

Back to the axial chokes as transformers:

I've been doing some experimenting with different oscillator topologies with a little success in the form of the cathode coupled Hartley using two of the chokes, but have run into if simply adding the values of the chokes together, having to make sure they have no inductive coupling. ( a 180 and 22uH choke pair that inductively couple are of course more than the sum of the two, though they don't need to be coupled in this form of oscillator). The waveform purity is fairly good but the amplitude stability with change of frequency is abysmal

Tuned grid oscillators that I've tried with the method have had dire waveform purity, that is down to too much gain and also the self resonance of the choke used for a coupling coil, the amplitude distortion in this case could be controlled by a simple AGC system controlling the grid bias, (best with a sharp cut off valve ironically )

A shunt fed tuned anode oscillator is yet to be tried, as least with that the amplitude variation can be minimised by balancing the anode load resistance....

I wanted to get the best performance from the local oscillator as is possible, as I've noticed a lot of commercial radios are bad in this respect and the conversion efficiency suffers badly in the FC stage as a result...

I wanted to do this whole front end and IF using those chokes as it would make the design reproducible.

More later...

Amie.