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Old 8th Jan 2021, 11:58 am   #10
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: 'Proper' DAB conversion for valve radios

Hmmm, now how would one of those work?

A small oscillator circuit to run with the LO tank of the set feeding a frequency counter and that will give a digital word used for station selection.

A normal DAB chipset, but it would need to be a pretty low power consumption one.

Rectify and regulate the heater supply to power it all.

Derive 455/465kHz from the counter clock then AM the sound onto it and feed through a DC block to the anode pin.

I don't suppose there is enough power available from HT via the anode and g2 feeds, so it has to be powered from the heater. 100mA string heaters bouncing up and down with a fair proportion of mains voltage must be awkward, though.

The 455/465kHz could be used to clock an SMPS with low risk of interfering with the IF.

David
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