Marconi 2022E

[electricspark]

Hi.

I wonder if anyone out there has experience with the Marconi 2022?

Mine works fine apart from the internal modulation frequency which is about 1.5% low on all three (400Hz, 1Khz & 5Khz) settings.  I don’t think there is an adjustment for it, so it must be a fault.

I would really appreciate any thoughts about where to look – I am assuming around IC36/a, C71/C72.

I spent ages trying to fix a radio with a poor SINAD only to find it was because the 2022 1K modulation was low, causing my SINAD meter to read too high!

[Andy Watson]

The internal modulation is provided by an RC-Wein oscillator. Tweaking either R or C should bring the frequency within range.
If frequency is the problem, why not use the external mod input? However, whichever source you use, the modulation signal is digitised to 8 bits - I think this will limit your SINAD measurements.

[electricspark]

Thanks for the response.

It seems I was a little pre-emptive – The 2022E spec says the mod frequency is +/- 5% or +/- 50Hz at 1Khz. So mine being 15Hz low was well within spec.  The problem was with my SINAD meter – I made the filter a tad narrow with only a 14Hz passband.

I added a trimmer across the R  in the 2022E oscillator and now the it starts at 998Hz cold and drifts upto 1001Hz once warmed up.

I had only recently acquired the 2022 and didn’t realise the mod freq. spec. was so wide.


Live & learn!