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Old 18th Feb 2020, 11:12 pm   #1
FERNSEH
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Default One valve FM tuners.

An article in the 1999 March/April GFGF magazine describes the operation of single valve FM radio adaptors that were marketed in West Germany in the early fifties. These receivers employ a special quenching oscillator which operates at around 30Kc/s.
In the UK Osmor marketed the "Mini Magic" FM tuner. The valve used in this receiver was an ECC81. I don't have the circuit for this receiver but here is an explanation how the circuit works:

A brief explanation of the circuit will show a simple ECC81 (12AT7), one half functioning as a superhet local oscillator @ 22m/c above signal frequency V1b) and the other half (V1a) as a super-regenerative detector @ 22m/c with a quench frequency of 30m/c. Discrimination of the 22m/c FM/IF signal is aceived by it's conversion to A.M. on the side skirts of I.F. the of the response curve and subsequent detection.


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Old 18th Feb 2020, 11:33 pm   #2
dave_n_t
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Default Re: One valve FM tuners.

I believe this is the Fremodyne circuit. A search will show up lots of references; I believe it was also one of G.A. French's(*) 'Suggested Circuits' in Radio Constructor.

dave
(*) a.k.a. J.R. Davies, of Smithy and dick fame.
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Old 18th Feb 2020, 11:51 pm   #3
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Default Re: One valve FM tuners.

From the GFGF article, a 1935 circuit proposition employing the quench oscillator technique.

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Old 19th Feb 2020, 8:07 am   #4
Ed_Dinning
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Default Re: One valve FM tuners.

Hi David, was there not a pulse counting design in PW or WW in the 60's that only used 1 valve ?

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Old 19th Feb 2020, 10:08 am   #5
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Default Re: One valve FM tuners.

It does sound like a Fremodyne, and the circuit is consistent with this.

I suspect the Fremodyne has few technical merits (one of them being that it won't splurge super-regen type RFI across the band of interest and spoil it for other people close by; instead it will wipe out the 22MHz band). But it might have been arguably sufficiently different from super-regen, that it could be used without infringing Armstrong's patents.

I've been playing with super-regen FM circuits, in collaboration with a talented youngster from another Forum, with good results!
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Old 19th Feb 2020, 11:21 am   #6
FERNSEH
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Default Re: One valve FM tuners.

Quote:
Originally Posted by dave_n_t View Post
I believe this is the Fremodyne circuit. A search will show up lots of references; I believe it was also one of G.A. French's(*) 'Suggested Circuits' in Radio Constructor.

dave
(*) a.k.a. J.R. Davies, of Smithy and dick fame.
From the Radiomuseum, information about the Fremodyne FM tuner:

https://www.radiomuseum.org/forum/fr..._detector.html

Hi Ed, I seem to remember the circuit of the pulse counting FM receiver was in a Radio Constructor magazine.

DFWB.

Last edited by FERNSEH; 19th Feb 2020 at 11:31 am.
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Old 19th Feb 2020, 11:21 am   #7
crackle
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Default Re: One valve FM tuners.

Circuit in the Radio Museum.
https://www.radiomuseum.org/r/schaub...satz_ue52.html

mike
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Old 19th Feb 2020, 11:35 am   #8
boxdoctor
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Default Re: One valve FM tuners.

Re Ed Dinning's comment:
I built a pulse-counting type FM tuner in the early sixties.
I do remember that the I.F. was at a rather low requency (< 120 Khz) rather than c.a. 100 Mhz). It was my own design, based on several articles I had read on the topic, and used two I.F. stages using EF80s, and worked rather well, except for the lack of any A.F.C. Tony.
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Old 19th Feb 2020, 11:58 am   #9
FERNSEH
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Default Re: One valve FM tuners.

From the American Radio History website, the November 1964 Radio Constructor magazine. On pages 253 to 256 construction details of an FM receiver which has a pulse counting detector:

https://www.americanradiohistory.com...RC-1964-11.pdf
The standard 10.7Mhz IF is converted down to 200Khz.

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Old 19th Feb 2020, 1:02 pm   #10
FERNSEH
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Default Re: One valve FM tuners.

Circuit diagram of the Schaub UE52 FM tuner:

https://nvhrbiblio.nl/schema/Schaub_UE52.pdf

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