>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?


OK, My english may cause confusion. So. here is the new statement of this
problem.

I am designing frequency tracking system using DFT filters(single bin).
For constant frequency, by iteration of DFT filters(from wide to narrow
filtering), it is able to track the frequency from the constant frequency
of signal stream.

Now, the frequency changes depending on a switch. For example, when it is
ON, frequnecy becomes A and when it is off, B. Now, I have to track
frequency A when the switch is ON. one problem is the switch is ON and OFF,
frequently and random.

I have 2 inputs, digitized signal source and the switch. Initially, I
collected digitized signal when switch is ON. The collected data has, of
course, same frequency A, but, there are phase discontinuity when switch
changes, which causes a problem to track frequency. Now, I would like to
some advice how to track frequency of phase discontinued signal. Or at
least, how to solve phase discontinuity problem in order to make smooth
signals. I considered windowing techniques, but it still doesn't work
because I don't when the window can be applied due to random switch
changes.

I hope it ie clear.

thanks.
Tim





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