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

Synchrodyne · 17th Jun 2012, 9:41 am

Referring back to my original question, about the use or not of a tank circuit in the reference carrier channel of quasi-synchronous demodulators, I have recently come across the data for the Siemens TDA2460-2 TV sound IF IC, which seems to be a successor to the original TBA460, and handles both AM sound and intercarrier FM sound channels. In the AM case, the quasi-synchronous demodulator may be used with or without a tank circuit, the latter allowing deletion of an LC circuit and the need to tune it. It was claimed that the LC circuit was unnecessary because of the excellent capture ratio features of the limiter. Working back from that, one might infer that with earlier ICs such as the TBA460, the need for a tank circuit with symmetrical AM signals such as TV AM sound was to correct for less-than-ideal limiter performance. And good limiter performance is harder to obtain at higher frequencies.

Cheers,

17th Jun 2012, 9:41 am	#15
Synchrodyne Nonode Join Date: Jan 2009 Location: Papamoa Beach, Bay of Plenty, New Zealand Posts: 2,944	Re: Quasi-Synchronous Demodulation Referring back to my original question, about the use or not of a tank circuit in the reference carrier channel of quasi-synchronous demodulators, I have recently come across the data for the Siemens TDA2460-2 TV sound IF IC, which seems to be a successor to the original TBA460, and handles both AM sound and intercarrier FM sound channels. In the AM case, the quasi-synchronous demodulator may be used with or without a tank circuit, the latter allowing deletion of an LC circuit and the need to tune it. It was claimed that the LC circuit was unnecessary because of the excellent capture ratio features of the limiter. Working back from that, one might infer that with earlier ICs such as the TBA460, the need for a tank circuit with symmetrical AM signals such as TV AM sound was to correct for less-than-ideal limiter performance. And good limiter performance is harder to obtain at higher frequencies. Cheers,