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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 15th Nov 2019, 1:31 pm   #1
mole42uk
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Default Mystery radio circuit?

I found this in an old scrapbook, drawn by myself, probably around 1975 but I have no idea what it is part of - does anyone recognise it?
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Old 15th Nov 2019, 1:49 pm   #2
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Default Re: Mystery radio circuit?

Quote:
Originally Posted by mole42uk View Post
I found this in an old scrapbook, drawn by myself, probably around 1975 but I have no idea what it is part of - does anyone recognise it?
It is easy to see it is likely a MW radio, from the 335pF tuning capacitor and the padder capacitor value which is in a sensible range for the MW band, but a tad low , so it could tune from over 2MHz depending on the coils.

The mixer IC is a classic crossed collector 4 quadrant multiplier type Gilbert cell with features analogous to the MC1496. Perhaps it was an experiment to play with the mixer IC , a fet L/O and a grounded gate RF amplifier.
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Old 15th Nov 2019, 4:49 pm   #3
G8HQP Dave
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Default Re: Mystery radio circuit?

Topband or 80m direct-conversion receiver front-end?
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Old 15th Nov 2019, 6:17 pm   #4
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Default Re: Mystery radio circuit?

1.4MHz IF Product Detector got my vote.
Or on reflection maybe not... why would you need any padder capacitors on that.
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Old 17th Nov 2019, 1:58 pm   #5
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Default Re: Mystery radio circuit?

There's an antenna in the schematic, so it must be a receiver of some kind.
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Old 17th Nov 2019, 2:44 pm   #6
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Default Re: Mystery radio circuit?

The capacitance of those MVAM varactors points at medium wave, possibly topband.

Lack of outputs shown for the mixer chip misses some clues that could have been there. The padder suggests it is the mixer stage of a superhet.

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Old 17th Nov 2019, 6:19 pm   #7
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Default Re: Mystery radio circuit?

I don't see that as antenna, all 3 lines would be equal length in my version of that symbol.

That looks like it is just "sig in" to me.
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Old 17th Nov 2019, 7:03 pm   #8
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Default Re: Mystery radio circuit?

You will find this very same circuit on page 312 of Elektor march 1976 via the Americanradiohistory. com website. Its the front end of a Super Plam phased lock loop type receiver.
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Old 18th Nov 2019, 11:16 am   #9
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Superb detective work!
Now I just have to wonder why I copied the diagram and what I was trying to do?
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Old 18th Nov 2019, 2:19 pm   #10
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Default Re: Mystery radio circuit?

Someone else's copy; save a few pennies?
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