UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - FM to AM converter

Graham G3ZVT · 20th Sep 2018, 9:55 pm

I should like to see the schematic of that modulator. It looks about as simple as you can get, and as such will have a degree of FM imparted to the signal as well as the intended AM.

I also have a pantry transmitter project in mind for when I get "a round tuit".

I have been very impressed with the AM sound from my 405 line TV modulator which operates around 50MHz. The oscillator is free-running, as is yours, but drift, even at this low VHF frequency is not a problem, and I can listen to the carrier on a communication receiver with the BFO switched on and the note is pure with near 100% modulation applied.

I see no reason why it wouldn't work at 1MHz with the appropriate tank circuit and a PA stage to put out a few miliwatts.
Uses an MC1374, the lower half of this cct

http://www.earlytelevision.org/405_modulator.html

20th Sep 2018, 9:55 pm	#2
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,724	Re: FM to AM converter - variation on a theme! I should like to see the schematic of that modulator. It looks about as simple as you can get, and as such will have a degree of FM imparted to the signal as well as the intended AM. I also have a pantry transmitter project in mind for when I get "a round tuit". I have been very impressed with the AM sound from my 405 line TV modulator which operates around 50MHz. The oscillator is free-running, as is yours, but drift, even at this low VHF frequency is not a problem, and I can listen to the carrier on a communication receiver with the BFO switched on and the note is pure with near 100% modulation applied. I see no reason why it wouldn't work at 1MHz with the appropriate tank circuit and a PA stage to put out a few miliwatts. Uses an MC1374, the lower half of this cct http://www.earlytelevision.org/405_modulator.html __________________ -- Graham. G3ZVT