NE567 as Am Fm demodulator question

[dr pepper]

Can someone confirm if my understanding is coorect.
Inside the Ne567 there are 2 phase comparators I & Q, you can use the loop filter voltage from these to dermodulate Am and Fm signals, Ok.

Am I correct in saying the Q phase comparator only recognizes shift in frequency rather than a shift in amplitude as its 'looking' at the crest/trough of the wave where there are no changes in time with amplitude mod.
And for Fm the I phase comparartor is able to detect shifts in amplitude as its looking at the zero cross point where a change in amplitude does create a change in time for the zero cross.

Its taken me a while to get the 'hang' if I & Q, I'll be pleased if I got this even just part correct.

 

[FvM]

You got the function basically right, but you should consider that the chip is designed as tone decoder (on-off switching) rather than linear AM demodulator. The PLL should work as a halfway linear FM detector.

 

[dr pepper]

Ok thanks.
Yeah I know the '567 is a tone decoder not a demod chip, I was more interested with understanding the concept of the I & Q sections within the chip.

 

[dr pepper]

I think I get this a little better now.
The Q section of the Pll recovers the carrier, and gives a steady unmodulated version of it.
The I section of the chip acts as a multiplier much in the same manner as a switching mixer would, it multiplies the phase shifted recovered carrier with the modulated Rf signal, the loop filter then removes the recovered carrier leaving audio.

 

[Aussie Susan]

I think you are looking for an overly simplistic interpretation of the I and Q signals.
Can I suggest that you look this up on the Internet - http://whiteboard.ping.se/SDR/IQ seems (at a quick glance) to show what the signals are all about, and even show how AM and FM are represented.
Susan

 

[dr pepper]

A typical theoretical explanation thanks Sue.
Interesting to see I & Q as a 3d chart.
Looking at the Am modulated I & Q signals you can see why the Pll is needed to regenerate the transmitted carrier.
Mixing it with the modulated signal then demodulates the Am audio.
W2aew has a couple of good vids on the subject.