Forums

FM Demodulation

Started by Randy Yates January 17, 2007
Gentle and Wise Readers of comp.dsp,

Two ways to demodulate FM are:

  1. Find the instantaneous phase (e.g., by examining the phase of the
  analytic signal) and compute the phase differences, i.e, f = dtheta/dt.

  2. Lock a PLL to the FM signal and use the VCO control voltage as the
  demodulated signal.

It seems to me that method 1 is much simpler. Why would anyone do FM
demodulation via method 2?

Let me state up front that I have an idea, but I'd rather get others'
ideas first without biasing them.
-- 
%  Randy Yates                  % "She tells me that she likes me very much,
%% Fuquay-Varina, NC            %     but when I try to touch, she makes it
%%% 919-577-9882                %                            all too clear."
%%%% <yates@ieee.org>           %        'Yours Truly, 2095', *Time*, ELO  
http://home.earthlink.net/~yatescr
Randy Yates <yates@ieee.org> wrote in news:m3wt3ltfzc.fsf@ieee.org:

> Gentle and Wise Readers of comp.dsp, > > Two ways to demodulate FM are: > > 1. Find the instantaneous phase (e.g., by examining the phase of the > analytic signal) and compute the phase differences, i.e, f = dtheta/dt. > > 2. Lock a PLL to the FM signal and use the VCO control voltage as the > demodulated signal. > > It seems to me that method 1 is much simpler. Why would anyone do FM > demodulation via method 2? > > Let me state up front that I have an idea, but I'd rather get others' > ideas first without biasing them.
Hardware needs vs software needs? -- Scott Reverse name to reply
Randy Yates wrote:
> Gentle and Wise Readers of comp.dsp, > > Two ways to demodulate FM are: > > 1. Find the instantaneous phase (e.g., by examining the phase of the > analytic signal) and compute the phase differences, i.e, f = dtheta/dt. > > 2. Lock a PLL to the FM signal and use the VCO control voltage as the > demodulated signal. > > It seems to me that method 1 is much simpler. Why would anyone do FM > demodulation via method 2? > > Let me state up front that I have an idea, but I'd rather get others' > ideas first without biasing them. > -- > % Randy Yates % "She tells me that she likes me very much, > %% Fuquay-Varina, NC % but when I try to touch, she makes it > %%% 919-577-9882 % all too clear." > %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO > http://home.earthlink.net/~yatescr
The SNR threshold is lower with a PLL. Search for "Threshold Extension" for details. John
Randy Yates wrote:
> Gentle and Wise Readers of comp.dsp, > > Two ways to demodulate FM are: > > 1. Find the instantaneous phase (e.g., by examining the phase of the > analytic signal) and compute the phase differences, i.e, f = dtheta/dt. > > 2. Lock a PLL to the FM signal and use the VCO control voltage as the > demodulated signal. > > It seems to me that method 1 is much simpler. Why would anyone do FM > demodulation via method 2? > > Let me state up front that I have an idea, but I'd rather get others' > ideas first without biasing them. > -- > % Randy Yates % "She tells me that she likes me very much, > %% Fuquay-Varina, NC % but when I try to touch, she makes it > %%% 919-577-9882 % all too clear." > %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO > http://home.earthlink.net/~yatescr
The SNR threshold is lower with a PLL. Search for "Threshold Extension" for details. John
sampson164@gmail.com writes:

> Randy Yates wrote: >> Gentle and Wise Readers of comp.dsp, >> >> Two ways to demodulate FM are: >> >> 1. Find the instantaneous phase (e.g., by examining the phase of the >> analytic signal) and compute the phase differences, i.e, f = dtheta/dt. >> >> 2. Lock a PLL to the FM signal and use the VCO control voltage as the >> demodulated signal. >> >> It seems to me that method 1 is much simpler. Why would anyone do FM >> demodulation via method 2? >> >> Let me state up front that I have an idea, but I'd rather get others' >> ideas first without biasing them. >> -- >> % Randy Yates % "She tells me that she likes me very much, >> %% Fuquay-Varina, NC % but when I try to touch, she makes it >> %%% 919-577-9882 % all too clear." >> %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO >> http://home.earthlink.net/~yatescr > > The SNR threshold is lower with a PLL. Search for "Threshold Extension" > for details.
That's it, John - that's what I was looking for. Apparently it's fairly well-known - I found it in [couch] after my original post It's apparently also known as FMFB (FM with feedback), which is referenced in both [couch] and [schwartcommtecniques]. Does anyone know how prevalent the PLL technique is in current demods (TVs, FM broadcast, etc.)? Is it pretty much standard fare now or are they somewhat unique? --Randy @BOOK{couch, title = "{Digital and Analog Communication Systems}", author = "{Leon~W.~Couch}", publisher = "Prentice Hall", edition = "fifth", year = "1993"} @book{schwartzcommtechniques, title = "Communication Systems and Techniques", author = "{Mischa Schwartz and William R. Bennett and Seymour Stein}", publisher = "IEEE Press (reissue, originally New York: McGraw-Hill 1966)", year = "1996"} -- % Randy Yates % "She tells me that she likes me very much, %% Fuquay-Varina, NC % but when I try to touch, she makes it %%% 919-577-9882 % all too clear." %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
sampson164@gmail.com writes:

> Randy Yates wrote: >> Gentle and Wise Readers of comp.dsp, >> >> Two ways to demodulate FM are: >> >> 1. Find the instantaneous phase (e.g., by examining the phase of the >> analytic signal) and compute the phase differences, i.e, f = dtheta/dt. >> >> 2. Lock a PLL to the FM signal and use the VCO control voltage as the >> demodulated signal. >> >> It seems to me that method 1 is much simpler. Why would anyone do FM >> demodulation via method 2? >> >> Let me state up front that I have an idea, but I'd rather get others' >> ideas first without biasing them. >> -- >> % Randy Yates % "She tells me that she likes me very much, >> %% Fuquay-Varina, NC % but when I try to touch, she makes it >> %%% 919-577-9882 % all too clear." >> %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO >> http://home.earthlink.net/~yatescr > > The SNR threshold is lower with a PLL. Search for "Threshold Extension" > for details.
That's it, John - that's what I was looking for. Apparently it's fairly well-known - I found it in [couch] after my original post It's apparently also known as FMFB (FM with feedback), which is referenced in both [couch] and [schwartcommtecniques]. Does anyone know how prevalent the PLL technique is in current demods (TVs, FM broadcast, etc.)? Is it pretty much standard fare now or are they somewhat unique? --Randy @BOOK{couch, title = "{Digital and Analog Communication Systems}", author = "{Leon~W.~Couch}", publisher = "Prentice Hall", edition = "fifth", year = "1993"} @book{schwartzcommtechniques, title = "Communication Systems and Techniques", author = "{Mischa Schwartz and William R. Bennett and Seymour Stein}", publisher = "IEEE Press (reissue, originally New York: McGraw-Hill 1966)", year = "1996"} -- % Randy Yates % "She tells me that she likes me very much, %% Fuquay-Varina, NC % but when I try to touch, she makes it %%% 919-577-9882 % all too clear." %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
sampson164@gmail.com writes:

> Randy Yates wrote: >> Gentle and Wise Readers of comp.dsp, >> >> Two ways to demodulate FM are: >> >> 1. Find the instantaneous phase (e.g., by examining the phase of the >> analytic signal) and compute the phase differences, i.e, f = dtheta/dt. >> >> 2. Lock a PLL to the FM signal and use the VCO control voltage as the >> demodulated signal. >> >> It seems to me that method 1 is much simpler. Why would anyone do FM >> demodulation via method 2? >> >> Let me state up front that I have an idea, but I'd rather get others' >> ideas first without biasing them. >> -- >> % Randy Yates % "She tells me that she likes me very much, >> %% Fuquay-Varina, NC % but when I try to touch, she makes it >> %%% 919-577-9882 % all too clear." >> %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO >> http://home.earthlink.net/~yatescr > > The SNR threshold is lower with a PLL. Search for "Threshold Extension" > for details.
That's it, John - that's what I was looking for. Apparently it's fairly well-known - I found it in [couch] after my original post It's apparently also known as FMFB (FM with feedback), which is referenced in both [couch] and [schwartcommtecniques]. Does anyone know how prevalent the PLL technique is in current demods (TVs, FM broadcast, etc.)? Is it pretty much standard fare now or are they somewhat unique? --Randy @BOOK{couch, title = "{Digital and Analog Communication Systems}", author = "{Leon~W.~Couch}", publisher = "Prentice Hall", edition = "fifth", year = "1993"} @book{schwartzcommtechniques, title = "Communication Systems and Techniques", author = "{Mischa Schwartz and William R. Bennett and Seymour Stein}", publisher = "IEEE Press (reissue, originally New York: McGraw-Hill 1966)", year = "1996"} -- % Randy Yates % "She tells me that she likes me very much, %% Fuquay-Varina, NC % but when I try to touch, she makes it %%% 919-577-9882 % all too clear." %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
sampson164@gmail.com writes:

> Randy Yates wrote: >> Gentle and Wise Readers of comp.dsp, >> >> Two ways to demodulate FM are: >> >> 1. Find the instantaneous phase (e.g., by examining the phase of the >> analytic signal) and compute the phase differences, i.e, f = dtheta/dt. >> >> 2. Lock a PLL to the FM signal and use the VCO control voltage as the >> demodulated signal. >> >> It seems to me that method 1 is much simpler. Why would anyone do FM >> demodulation via method 2? >> >> Let me state up front that I have an idea, but I'd rather get others' >> ideas first without biasing them. >> -- >> % Randy Yates % "She tells me that she likes me very much, >> %% Fuquay-Varina, NC % but when I try to touch, she makes it >> %%% 919-577-9882 % all too clear." >> %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO >> http://home.earthlink.net/~yatescr > > The SNR threshold is lower with a PLL. Search for "Threshold Extension" > for details.
That's it, John - that's what I was looking for. Apparently it's fairly well-known - I found it in [couch] after my original post It's apparently also known as FMFB (FM with feedback), which is referenced in both [couch] and [schwartcommtecniques]. Does anyone know how prevalent the PLL technique is in current demods (TVs, FM broadcast, etc.)? Is it pretty much standard fare now or are they somewhat unique? --Randy @BOOK{couch, title = "{Digital and Analog Communication Systems}", author = "{Leon~W.~Couch}", publisher = "Prentice Hall", edition = "fifth", year = "1993"} @book{schwartzcommtechniques, title = "Communication Systems and Techniques", author = "{Mischa Schwartz and William R. Bennett and Seymour Stein}", publisher = "IEEE Press (reissue, originally New York: McGraw-Hill 1966)", year = "1996"} -- % Randy Yates % "She tells me that she likes me very much, %% Fuquay-Varina, NC % but when I try to touch, she makes it %%% 919-577-9882 % all too clear." %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
sampson164@gmail.com writes:

> Randy Yates wrote: >> Gentle and Wise Readers of comp.dsp, >> >> Two ways to demodulate FM are: >> >> 1. Find the instantaneous phase (e.g., by examining the phase of the >> analytic signal) and compute the phase differences, i.e, f = dtheta/dt. >> >> 2. Lock a PLL to the FM signal and use the VCO control voltage as the >> demodulated signal. >> >> It seems to me that method 1 is much simpler. Why would anyone do FM >> demodulation via method 2? >> >> Let me state up front that I have an idea, but I'd rather get others' >> ideas first without biasing them. >> -- >> % Randy Yates % "She tells me that she likes me very much, >> %% Fuquay-Varina, NC % but when I try to touch, she makes it >> %%% 919-577-9882 % all too clear." >> %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO >> http://home.earthlink.net/~yatescr > > The SNR threshold is lower with a PLL. Search for "Threshold Extension" > for details.
That's it, John - that's what I was looking for. Apparently it's fairly well-known - I found it in [couch] after my original post It's apparently also known as FMFB (FM with feedback), which is referenced in both [couch] and [schwartcommtecniques]. Does anyone know how prevalent the PLL technique is in current demods (TVs, FM broadcast, etc.)? Is it pretty much standard fare now or are they somewhat unique? --Randy @BOOK{couch, title = "{Digital and Analog Communication Systems}", author = "{Leon~W.~Couch}", publisher = "Prentice Hall", edition = "fifth", year = "1993"} @book{schwartzcommtechniques, title = "Communication Systems and Techniques", author = "{Mischa Schwartz and William R. Bennett and Seymour Stein}", publisher = "IEEE Press (reissue, originally New York: McGraw-Hill 1966)", year = "1996"} -- % Randy Yates % "She tells me that she likes me very much, %% Fuquay-Varina, NC % but when I try to touch, she makes it %%% 919-577-9882 % all too clear." %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
sampson164@gmail.com writes:

> Randy Yates wrote: >> Gentle and Wise Readers of comp.dsp, >> >> Two ways to demodulate FM are: >> >> 1. Find the instantaneous phase (e.g., by examining the phase of the >> analytic signal) and compute the phase differences, i.e, f = dtheta/dt. >> >> 2. Lock a PLL to the FM signal and use the VCO control voltage as the >> demodulated signal. >> >> It seems to me that method 1 is much simpler. Why would anyone do FM >> demodulation via method 2? >> >> Let me state up front that I have an idea, but I'd rather get others' >> ideas first without biasing them. >> -- >> % Randy Yates % "She tells me that she likes me very much, >> %% Fuquay-Varina, NC % but when I try to touch, she makes it >> %%% 919-577-9882 % all too clear." >> %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO >> http://home.earthlink.net/~yatescr > > The SNR threshold is lower with a PLL. Search for "Threshold Extension" > for details.
That's it, John - that's what I was looking for. Apparently it's fairly well-known - I found it in [couch] after my original post It's apparently also known as FMFB (FM with feedback), which is referenced in both [couch] and [schwartcommtecniques]. Does anyone know how prevalent the PLL technique is in current demods (TVs, FM broadcast, etc.)? Is it pretty much standard fare now or are they somewhat unique? --Randy @BOOK{couch, title = "{Digital and Analog Communication Systems}", author = "{Leon~W.~Couch}", publisher = "Prentice Hall", edition = "fifth", year = "1993"} @book{schwartzcommtechniques, title = "Communication Systems and Techniques", author = "{Mischa Schwartz and William R. Bennett and Seymour Stein}", publisher = "IEEE Press (reissue, originally New York: McGraw-Hill 1966)", year = "1996"} -- % Randy Yates % "She tells me that she likes me very much, %% Fuquay-Varina, NC % but when I try to touch, she makes it %%% 919-577-9882 % all too clear." %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr