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4046 PLL

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SGiard

Member
Hi,

I have looked all over the Internet for a schematic of an FM receiver in the commercial band (88mhz to 108mhz) based on 4046 PLL chip or variant thereof.

Does anybody know of a such a schematic?

Thanks.
 

crutschow

Well-Known Member
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The 4046 is a low frequency PLL.
I don't see how it would be used in a commercial band FM receiver. :confused:
 

Les Jones

Well-Known Member
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Hi cruts,
It would be possible to use a 4046 to demodulate FM in a superhet receiver if the final IF frequency was low enough. In the early 1970s Pye made the "Pockefone" receiver which was a double superhet. The first conversion was down from around 450 Mhz to a first IF of 10.7 Mhz. The second conversion was from 10.7 Mhz down to 100Khz and that was demodulated using a charge pump. The charge pump detector could be replaced with a 4046 phase locked loop. I have no idea why the OP wants to this but he could add a second coversion stage to a normal FM receiver which will probably have 10.7 Mhz IF followed by a discriminator.

Les.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hi cruts,
It would be possible to use a 4046 to demodulate FM in a superhet receiver if the final IF frequency was low enough. In the early 1970s Pye made the "Pockefone" receiver which was a double superhet. The first conversion was down from around 450 Mhz to a first IF of 10.7 Mhz. The second conversion was from 10.7 Mhz down to 100Khz and that was demodulated using a charge pump.
I'm not quite sure why you mentioned the Pye Pocketfone?, double conversion was the standard technique for NBFM receivers for obvious reasons (lowering the IF makes the modulation a higher percentage of the carrier).

The only 'interesting' thing about it was the 100KHz second IF (perhaps because of the charge pump?), usually the second IF is the standard 455/470KHz 'AM' type frequency.

As for the 4046, while it would probably be fine for NBFM, I doubt it would be any use for WBFM.

You 'could' utilise the 4046 in the tuning for an FM receiver, but essentially you would only be using the phase detector driving an external VCO.

But basically you don't find circuits for FM radios using the 4046 because it's a VERY poor choice, there are (or at least were) far better chips available for doing that.
 

Les Jones

Well-Known Member
Most Helpful Member
Hi Nigel,
I totaly agree that the 4046 is a very poor choice as an FM demodulator. I was just suggesting a way it could be used. It's a bit like another thread where someone wants to use Nixie tubes for a calculator display.

Les.
 

SGiard

Member
Thanks a lot guys. The 4046 being unable to handle the 10Mhz IF explains why I could not fond anything.

The back story is I inherited a trove of electronics component in which there was an incomplete breadboard with an op amp, a 4046 PLL, a mc145151p2 frequency synth with a 10.24Mhz crystal and an lm386 audio amp. The 145151 is set to divide the 10.24 mhz by 2048 (which gives 5000) and the external input frequency (from the 4046 PLL's VCO) by 5000. The phase difference output of the 145151 is fed thru a filter to the VCO in of the 4046 and to the LM386. The phase comparator of the 4046 is not used.

I thought it might be some kind of monaural FM receiver and was wondering if I could find the complete schematic for it cause some parts seem to be missing.

Anybody has any ideas, what that circuit was?
 

dr pepper

Well-Known Member
Most Helpful Member
The 4046 is fairly slow, but the 'hc4046 goes much higher and might well work well at 10.7mc.
I built a frequency standard recently that uses a 'hc4046 to up 1mhz to 3mhz, at first I tried 1mhz to 6mhz and it worked fine.
I agree with nige though this ic probably isnt so great for fm audio demod, but it more than likely is possible.
 
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