UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Quasi-Synchronous Demodulation

Synchrodyne · 25th Jul 2010, 12:33 pm

Talking of professional tuners, the attached block schematic for the BBC RC1/511 (from Electronics & Wireless World, July 1984) shows some interesting facets in respect of quasi-synchronous demodulation.

I would guess that it uses semi-discrete circuitry, with small-scale, essentially monofunctional ICs. The vision reference carrier channel appears to combine amplitude limiting, careful bandwidth limiting (0.5 MHz) as well as centring of the passband over the vision carrier, thus removing any adverse effects of the Nyquist slope in the earlier SAW filter stage. There is a separate multiplier for the sound carrier, which is separated from the vision carrier early on, with the 6.0 MHz output described as “true intercarrier”.

Cheers,

25th Jul 2010, 12:33 pm	#3
Synchrodyne Nonode Join Date: Jan 2009 Location: Papamoa Beach, Bay of Plenty, New Zealand Posts: 2,944	Re: Quasi-Synchronous Demodulation Talking of professional tuners, the attached block schematic for the BBC RC1/511 (from Electronics & Wireless World, July 1984) shows some interesting facets in respect of quasi-synchronous demodulation. I would guess that it uses semi-discrete circuitry, with small-scale, essentially monofunctional ICs. The vision reference carrier channel appears to combine amplitude limiting, careful bandwidth limiting (0.5 MHz) as well as centring of the passband over the vision carrier, thus removing any adverse effects of the Nyquist slope in the earlier SAW filter stage. There is a separate multiplier for the sound carrier, which is separated from the vision carrier early on, with the 6.0 MHz output described as “true intercarrier”. Cheers, Attached Thumbnails