28-09-2016, 01:17 PM
(This post was last modified: 28-09-2016, 01:18 PM by ppppenguin.)
The Freescale MC44BS373 chip in the Aurora, also used by David Robinson and others, can do AM sound but not with 3.5MHz spacing from vision. Presumably a French modulator would have needed a chip that did AM sound and the Freescale chip can do that. There may well have been others.
The common MC1374 is, I believe, FM sound only.
http://www.nxp.com/files/app_specific_st...4CC373.pdf
In theory the sound could be modulated on to a 3.5MHz subcarrier which is added to the vision ahead of the vision modulator. AKA intercarrier sound. The problems that afflict intercarrier demodulation are mainly absent, the only real requirement is for good linearity in the vision modulator to prevent sound/vision intermodulation. I wonder if the Meier design uses this approach. It would explain the lack of a 41.5MHz xtal. This method could be used with any vision modulator, chip or discrete, possibly including the MC1374 provided its sound modulator can be disabled.
The common MC1374 is, I believe, FM sound only.
http://www.nxp.com/files/app_specific_st...4CC373.pdf
In theory the sound could be modulated on to a 3.5MHz subcarrier which is added to the vision ahead of the vision modulator. AKA intercarrier sound. The problems that afflict intercarrier demodulation are mainly absent, the only real requirement is for good linearity in the vision modulator to prevent sound/vision intermodulation. I wonder if the Meier design uses this approach. It would explain the lack of a 41.5MHz xtal. This method could be used with any vision modulator, chip or discrete, possibly including the MC1374 provided its sound modulator can be disabled.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
