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

Synchrodyne · 31st Jul 2010, 6:57 am

Dave, thanks for that, which has certainly helped my understanding of the topic.

In the TV vision case I think that the use of AFC was pretty much assumed by Motorola when it designed the MC1330. The IC has a buffered, limited carrier output for feeding an AFC system. For American TV receivers, I think that AFC had been standard for many years, and in fact was one of the first functions for which ICS were developed. Later quasi-synchronous demodulator ICs, such as the TCA270 and TDA 2540/41, included the AFC function.

In HF receivers, I imagine that the ability to operate away from the correct tuning point may have been considered advantageous in terms of partially rejecting interference in one sideband. And a quasi-synchronous demodulator should have been better than a diode in such situations. So that could have been another reason for not using a tank circuit. AFC would have been rare in HF receivers (except for the point-to-point ISB type). I think that the Eddystone 1570/1590 was quite unusual in having AFC.

Incidentally, I had previously been under the impression that the term “quasi-synchronous”, if not actually coined by Motorola, came into widespread use because Motorola had associated it with the MC1330 IC. However, the term is not used in the IEE paper (by Lunn of Motorola). And in a later paper co-authored by Lunn (on the “Monomax” TV IC), the by-then conventional TV demodulator was referred to as being of the “pseudo-synchronous” type.

Cheers,

31st Jul 2010, 6:57 am	#5
Synchrodyne Nonode Join Date: Jan 2009 Location: Papamoa Beach, Bay of Plenty, New Zealand Posts: 2,944	Re: Quasi-Synchronous Demodulation Dave, thanks for that, which has certainly helped my understanding of the topic. In the TV vision case I think that the use of AFC was pretty much assumed by Motorola when it designed the MC1330. The IC has a buffered, limited carrier output for feeding an AFC system. For American TV receivers, I think that AFC had been standard for many years, and in fact was one of the first functions for which ICS were developed. Later quasi-synchronous demodulator ICs, such as the TCA270 and TDA 2540/41, included the AFC function. In HF receivers, I imagine that the ability to operate away from the correct tuning point may have been considered advantageous in terms of partially rejecting interference in one sideband. And a quasi-synchronous demodulator should have been better than a diode in such situations. So that could have been another reason for not using a tank circuit. AFC would have been rare in HF receivers (except for the point-to-point ISB type). I think that the Eddystone 1570/1590 was quite unusual in having AFC. Incidentally, I had previously been under the impression that the term “quasi-synchronous”, if not actually coined by Motorola, came into widespread use because Motorola had associated it with the MC1330 IC. However, the term is not used in the IEE paper (by Lunn of Motorola). And in a later paper co-authored by Lunn (on the “Monomax” TV IC), the by-then conventional TV demodulator was referred to as being of the “pseudo-synchronous” type. Cheers,