Forum: GNU Radio How to get the carrier's frequency offset in PM demodulator?

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.

Does gnuradio provide this function?
thank you

2013/1/29 adream <adream307@gmail.com>

I am feel sorry for no reply

2013/1/30 adream <adream307@gmail.com>

On Wed, Jan 30, 2013 at 9:30 AM, adream <adream307@gmail.com> 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 <adream307@gmail.com>
>
>> 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

On Wed, Jan 30, 2013 at 11:16 AM, Brian Padalino 
<bpadalino@gmail.com>wrote:

>
> On Wed, Jan 30, 2013 at 9:30 AM, adream <adream307@gmail.com> 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 <adream307@gmail.com>
>>> 2013/1/29 adream <adream307@gmail.com>
>>>> 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