On Fri, 16 Jan 2009 06:27:44 -0600, "akachyan" <[email protected]>
wrote:

>>akachyan wrote:
>>
>> ...
>>
>>> I use DFT filters to track frequency. FFT doesn't work in my case
>because
>>> I need precise frequency tracking.
>>
>>FFT is an efficient way to do DFT. If different ways to do DFT give
>>different results, at least one of them is wrong.
>
>I use single-bin DFT filter. FFT may be used. But for narrow bin,
>calculation can be brutal. :-)

Oh, the "single bin" makes a big difference. It uses much less
computation than computing all the bins of the DFT. As I recall,
that's often called a Goertzel filter.

>
>>
>>> Furthermore, the off signal may have different frquency, i.e on freq
>is
>>> 15.65 Mhz and off freq is 16.59 Mhz. In this case, I have to track
>15.65
>>> Mhz freq. of course it has on/off switches.
>>
>>If the off freq is 16.59 MHz, what does "off" really mean? Do you have a
>
>>form of FSK?
>
>It is interesting problem.
>
>For example, there is a switch. When it is ON, signal has 15.65MHz, when
>OFF, 16.59MHz. Presumely, system doesn't know the frequency beforehand.
> Now the system has to track the frequency,15.65Mhz when switch is ON. But
>switch is frequenctly on and off. So, I collected the signal when switch is
>on.

Are you trying to phase-lock on the 16.59 MHz signal, generating
your own signal with the same frequency and phase when the switch is
off?

Or, are you trying to decode the switch ON and Off positions and
times (this is indeed FSK, Frequency Shift Keying)? If so, you could
have filters for both frequencies, and have a comparison function that
tells which filter output is larger. Also, there are other ways to do
this.

>The collected signal has same frequency, but a lot of phase discontinuity.
>It makes me hard to track the frequency. It is the problem.

I hesitate to say this, as your English is surely much better than
my knowledge of your native language, but it appears your lack of
English skills are making it hard for me and others to understand your
problem and what you are trying to do. Can you restate the problem in
another way, or even several other ways?