# How to get the carrier's frequency offset in PM demodulator? **URL:** \ **Category:** GNU Radio\ **Created:** [January 29, 2013, 12:12pm UTC](https://www.ruby-forum.com/t/how-to-get-the-carriers-frequency-offset-in-pm-demodulator/225771 "2013-01-29T12:12:38Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![SSkonishi\_takurou\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/bb73d2/32.png) [@SSkonishi\_takurou\_S](https://www.ruby-forum.com/u/SSkonishi_takurou_S)\ **Post date:** [January 29, 2013, 12:12pm UTC](https://www.ruby-forum.com/t/how-to-get-the-carriers-frequency-offset-in-pm-demodulator/225771/1 "2013-01-29T12:12:38Z")
Hello, I am learning PM Demodulation, and someones tell me that the FM Demodulator in gnuradio can demodulate the PM signals. I want to get the carrier’s frequency offset in PM demodulating, does gnuradio provide this function? For example, in my project, I set the frequency of IF signal is 70MHz, but the real input IF signal is 70.01MHz. In this case, I hope my program can print the carrier’s frequency offset, 10KHz Thank you. ---
**Author:** ![adream](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/53a042/32.png) [@adream](https://www.ruby-forum.com/u/adream)\ **Post date:** [January 30, 2013, 1:23pm UTC](https://www.ruby-forum.com/t/how-to-get-the-carriers-frequency-offset-in-pm-demodulator/225771/2 "2013-01-30T13:23:32Z")
Does gnuradio provide this function? thank you 2013/1/29 adream [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![adream](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/53a042/32.png) [@adream](https://www.ruby-forum.com/u/adream)\ **Post date:** [January 30, 2013, 3:31pm UTC](https://www.ruby-forum.com/t/how-to-get-the-carriers-frequency-offset-in-pm-demodulator/225771/3 "2013-01-30T15:31:39Z")
I am feel sorry for no reply 2013/1/30 adream [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![adream](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/53a042/32.png) [@adream](https://www.ruby-forum.com/u/adream)\ **Post date:** [January 30, 2013, 5:18pm UTC](https://www.ruby-forum.com/t/how-to-get-the-carriers-frequency-offset-in-pm-demodulator/225771/4 "2013-01-30T17:18:06Z")
On Wed, Jan 30, 2013 at 9:30 AM, adream [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I am feel sorry for no reply It’s just been a day - sometimes if the answer doesn’t come quickly, people are confused by what you’re asking. > 2013/1/30 adream [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > > > Does gnuradio provide this function? > > thank you Natively I don’t think it does, but there are properties to the demodulated signal you may be able to exploit and calculate it. > > > In this case, I hope my program can print the carrier’s frequency > > > offset, 10KHz > > > Thank you. FM has the property that frequency offset results in a DC offset at the demodulated signal that is proportional to the amount of frequency offset (given the input signal has no DC component). For PM, since you are not taking the first derivative of the phase as you are with FM, the DC component will be shifted up to your frequency offset. Doing a long term average of a demodulated FM signal should (hopefully!) come out to be 0 for no frequency offset. You could FM demodulate, put a DC filter then reintegrate at the output to get your PM signal back - but I am not sure how well that works. Give it a shot and let us know! Hope that helped. Brian ---
**Author:** ![adream](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/53a042/32.png) [@adream](https://www.ruby-forum.com/u/adream)\ **Post date:** [February 1, 2013, 4:50am UTC](https://www.ruby-forum.com/t/how-to-get-the-carriers-frequency-offset-in-pm-demodulator/225771/5 "2013-02-01T04:50:35Z")
On Wed, Jan 30, 2013 at 11:16 AM, Brian P. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: > On Wed, Jan 30, 2013 at 9:30 AM, adream [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > I am feel sorry for no reply > > It’s just been a day - sometimes if the answer doesn’t come quickly, > people are confused by what you’re asking. True. A lot of us are also very busy with other things and can’t come rushing to answer all questions. > 2013/1/30 adream [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > > > 2013/1/29 adream [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > > > > > > > Thank you. > > You could FM demodulate, put a DC filter then reintegrate at the output to > get your PM signal back - but I am not sure how well that works. Give it a > shot and let us know! > > Hope that helped. > > Brian And remember, there are also the PLL blocks. Tom