UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Does anyone know anything about "Modulation Depth"? (Philips PM5680)

Radio Wrangler · 6th Oct 2022, 3:55 pm

PAL-I has FM sound, so the amount of FM is specified as the frequency deviation, usually in kHz.

Vision is amplitude modulated with the sync pulses being the greatest amplitude. With a colour signal, there has to be allowance in carving-up the amplitude cake to allow for the maximum chrominance voltage at 4.43361874MHz superimposed on the luminance ( DC component).

Video isn't a symmetrical easy waveform like a sine or AC-coupled AM audio, It will have to undergo DC restoration at the receiver. So it's best to not think of an average carrier level. Think of the RF voltage at peak sync and the RF level at the black reference in the porches and scale everything from these.

David

6th Oct 2022, 3:55 pm	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,917	Re: Does anyone know anything about "Modulation Depth"? (Philips PM5680) PAL-I has FM sound, so the amount of FM is specified as the frequency deviation, usually in kHz. Vision is amplitude modulated with the sync pulses being the greatest amplitude. With a colour signal, there has to be allowance in carving-up the amplitude cake to allow for the maximum chrominance voltage at 4.43361874MHz superimposed on the luminance ( DC component). Video isn't a symmetrical easy waveform like a sine or AC-coupled AM audio, It will have to undergo DC restoration at the receiver. So it's best to not think of an average carrier level. Think of the RF voltage at peak sync and the RF level at the black reference in the porches and scale everything from these. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done