[ARC5] [BoatAnchors] OK Smart People- FM Demodulator

[Bill Fuqua]

   The specific example I just looked up was for a SA615.
The coupling capacitor was 10pF and at 455kHz its reactance is 35kOhms.
That is more than 10 times the input resistance of the internal product
detector. That is where the additional 90 degrees of phase shift comes from.
   Your answer made me think about it since until now I had not given it much
thought. Thanks for your response.

73
Bill wa4lav


At 01:54 PM 1/18/2013 -0500, Bill Fuqua wrote:
>Your post went to the wrong list. It went to boat anchors.
>Now I see where the comment from
>   However, if the coupling capacitor's reactance is small compared to the 
> resistance (at resonance) of the
>load, the tuned circuit and input resistance of the detector, an 
>additional near 90 degree phase shift will
>be introduced.
>73
>Bill wa4lav
>
>At 09:15 AM 1/18/2013 -0800, you wrote:
>>Dave, if L1-C5 was resonant at the frequency you want to demodulate the
>>phase shift would be zero degrees, not 90 degrees.  You could think of a
>>quadrature detector as functioning something like slope FM demodulation with
>>an AM receiver where you tune the signal to the sloping skirt of the IF
>>bandpass where frequency variation will produce amplitude variation to the
>>AM detector.
>>
>>Arden Allen
>>KB6NAX
>>
>>If you get to thinking you're a person of
>>some influence, try ordering somebody
>>else's dog around.  -Will Rogers
>>
>> > ....
>>..
>>http://jaunty-electronics.com/blog/2012/08/no-tune-ne602-ne612-fm-demodulator/
>>
>>It's supposed to work between 420-500 KC.
>>I'm hoping to "tweak" something like this for 15 MC,
>>since the NE602 / NE612 will work well into UHF.
>>What puzzles me is the tank circuit L1 / C5.
>>820 uH and 100 pF resonate at 555 KC.
>>Is that right?  And if so, what resonant freq would
>>one use to get the thing to work at 15 MC?
>>
>>73 DE Dave AB5S
>>
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