# phase modulation/demodulation ?

Discussion in 'General Electronics Chat' started by Mathematics!, Jan 13, 2010.

1. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
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Ok , we have for all the ways to do demodulation
AM
product dectectors (pretty easy to make i.e , product mixers , ...etc)
enevlope detectors (very easy to make diode detectors)

For FM
Slope detector ( not worth doing poor quality and is just offseting the carrier to pick up the equivalent changes in amplituded)
Ratio detectors
Foster-Seeley FM detectors
Phase locked loop (PLL)

For PM
???????????????????

Can somebody list all the ways known to detect phase modulation?
I don't even know one of these?

Also curious how you would do phase modulation???

I know FM and PM are similar and doing FM modulation modulates PM in someways (because changing the frequency changes the period as well)but curious to know if you could ever combined FM and PM together into a different modulation scheme? Kind of like QAM which combines AM and PM modulation together.
Basically I think you can combined (AM and PM) or (AM and FM) but not (FM and PM) as a modulation schematic but correct me if I am wrong?

So the only ways to modulate a wave would be
AM , FM , and PM or any combination except (PM and FM combo)

For the digital modulation schemes they would be just discrete cases of the above.

Ofcourse CW would just be a special case of digital modulation with 2 states on/off keying ....etc

The only other thing we can do is frequency hopping (ie. spectral spreading ,...etc) but these aren't different forms of modulation they are just switching carriers so they are harder to detect from an outsider reciver ,...etc

I think that is every modulation schematic possible. (other then using multiplexing techinques with more carriers ,...etc)
And I am not talking about PWM ,...etc only wireless modulation schematics...

But really itching to know how they do PM modulation/demodulation since I never saw any schematic or discussion on how to do it and why?

Thanks for any help
Seems since FM is so close to PM I would think that the detectors for PM would be similar to the detectors for FM but that is just a guess?

Last edited: Jan 13, 2010
2. ### retched AAC Fanatic!

Dec 5, 2009
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geez-a-wheez . I am trying to think of how you would DEmodulate P-FM.

Would the demodulator just see is as noise? Would it be more a form of encryption than modulation?

interested to see how this plays out.

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6. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
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I have read most of the stuff before and I get what the difference is mathematically between PM and FM.
The math formulas are as followed
for PM the phase is a function of time and the amplitude and frequency are not functions of time

In AM the frequency and phase are not functions of time and are kept constant

In FM the amplitude and phase are not functions of time and are kept constant.

Mathematically
PM
Asin($\varpi$*t + $\phi$(t) )

FM
Asin($\varpi(t)$*t + $\phi$ )

AM
A(t)sin($\varpi$*t + $\phi$ )

I know PM and FM both effect the other ...
because f = 1/T where T is the period or phase , f being the frequency.

My problem is I know how to detect/modulate AM and FM.

But I don't even know how to modulate/detect PM.
I cann't find anything on the net that talks about how to detect/modulate PM. They only talk about PM and not how to actually build a circuit that will detect it and why it detects it....

Like AM they have millions of sites talking about how you can modulate and detect it and show you how to build it , why it works ,...etc
Same with FM....
But for PM can somebody list some detectors or schematics for PM?

Both FM and PM are angle modulation schemes so it stands to reason that the detectors/modulators will be similar in principle but duno?

As for can FM and PM be used in combo for a modulation schematic or can you only use (AM with PM or FM in combo such an example is QAM) not (PM with FM in combo)? Still curious on this. If yes then I don't understand how the FM modulation won't interfer with the PM modulation.
When I mean together I mean we are using the same carrier wave and modulating it both with FM and PM kind....(like with QAM for AM and PM)
Don't really think you can ???? Yes/No

I know mathematically in the 3 latex formulas above you could vary the frequency and phase with respect to time but I am unsure in practice if you can vary the 2 togther? If you can then whats from stoping somebody from modulating a wave with all three AM,FM,PM all at once to make even more baud (symbols per second to transmit data , internet ,....etc )?

Ofcourse you can use 2 different carriers one with PM and the other with FM and multiplex them together but I mean only one carrier?

And last question is FM or PM more prown to interference/noise or are they about the same? ( would think they are the same since one effects the other slightly.....)