Thread: Redifon MCU6B
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Old 3rd Dec 2022, 10:11 pm   #2
Radio Wrangler
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Location: Fife, Scotland, UK.
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Default Re: Redifon MCU6B

I've no information on that unit, but can offer some general thoughts.

Low intermodulation distortion is important in a multicoupler, and this has been understood well for many years before that unit was built. It seems to use a push-pull pair of transistors in a transformer-coupled arrangement. Earlier units used power valves to get reasonable linearity. Those are probably 1-2W class TO-5 transistors. 2N5109 or 2N3866 for example. I'd have expected clip-on heatsinks on them.

An AGC arrangement, looking at the peak RF output voltage and controlling some variable gain element earlier in the chain wouldn't surprise me. The trouble is in getting low distortion in the variable gain section. In their transmitters, Redifon used to use long chains of diodes as variable impedance elements, but the linearity is not likely to be good enough for this application.

That large wound inductive thing seems out of place. Lots of inductance, but a low self-resonance frequency which doesn't suit 1-30MHz. I wonder if it is a saturable reactor or transformer where a ferrite core is driven into saturation to act as an attenuator, where the gain control sets the DC coil current?

David
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