10.7MHz FM TTL demodulator

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10.7MHz FM TTL demodulator Empty Re: 10.7MHz FM TTL demodulator

Post by Admin on Tue Jan 31, 2017 5:31 pm

Hello Rex,
Welcome to the sm0vpo forum.

If you are using any of the 74 family of TTL chips then 16mA sounds about right. But these chips are rated at 5V +/- 0.25V so your supply voltage may be a bit high. TTL is usually a bit critical.

Yes, you can use a CMOS chip to get the same logic function, that is an oscillator, but you may have to change the 22p and 1K0 pot component values in the oscillator a little to get the correct centre-frequency.

Also, the 7401 has open-collector outputs, so the 1K0 and 470R resistors in the comparator may be a bit low values for CMOS. Try multiplying them by 10. the 470R resistor you may be able to totally eliminate.

This is an old design and it was researched and built for an old project. I no-longer have the project available so I cannot give you a tried/tested reply to this. Please do let us all know how you get on with the project.

Very best regards from Harry - SM0VPO

They say that money cannot buy you happiness. But if you want to prove this by experiment, then I volunteer to be the test-rabbit :-)

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10.7MHz FM TTL demodulator Empty 10.7MHz FM TTL demodulator

Post by REXMAKRO on Tue Jan 31, 2017 11:12 am

Hi there! I 'd like to ask how much current this particular circuit is meant to draw? I can measure about 16mA with a 6 Volt supply... Is that right?? Also, would that be possible to substitute the (currently) obsolete SN7401 with another quad NAND gate??... Regards, Rex. ...


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