measuring frequencies

[Kumar]

Hi,

I want to measure changing frequencies of the alert tones of the mobile radio under test. I currently tried using the PCI 7035 card to tap do the acquisition and use the extract single tone VI to extract the frequencies, I put the code in the loop to keep on getting the frequencies from the radio. How do I get the frequency of the tone every milisecond. What should be the number of samples and the sampling rate be if I need the to detect the frequency every 1ms? Is there any other VI that does timing?

[PdB]

Do you really need a real-time response?
If not, have you looked at the Joint Time Frequency analysis functions?
If you sample for a long enough time with the right sample-freq., after acquisition, you can use these functions to plot frequency/intensity against time-stamp. Maybe it works for you.

[Kumar]

Yes, I am doing automatic testing on the alert tones of the radio. I need to do real-time decoding of the tone, identify it and send it to the test manager. What function is this (Joint Time Frequency analysis functions). Where can I find this fuction and how do I use it ? Thanks

[PdB]

http://zone.ni.com/devzone/conceptd.nsf/2d17d611efb58b22862567a9006ffe76/935878a7c6a0e4ff8625688f005b7a3c?OpenDocument

[Rob Cole]

I hope that you're not using the Windoze environment. Millisecond timing in Windoze if difficult to maintain. With all of the background tasks running and Windoze almost attempt at multitasking, time intervals can be very inconsistent.

I would also say to watch what frequencies that you are looking for. At 1ms a 500Hz tone is only half a cycle. Most frequency measuring algorithms, measure to the same point on the next cycle, so at 1ms, frequencies below 1kHz are not measurable. You may have to adjust your timing.

That being said, have fun.

Rob

[Tims]

Hi Kumar,

What you need is a frequency demodulator function, that will process the
changing frequency df/dt and convert it to a changing level dv/dt.

Tim

Kumar wrote:

> Hi,
>
> I want to measure changing frequencies of the alert tones of the
> mobile radio under test. I currently tried using the PCI 7035 card to
> tap do the acquisition and use the extract single tone VI to extract
> the frequencies, I put the code in the loop to keep on getting the
> frequencies from the radio. How do I get the frequency of the tone
> every milisecond. What should be the number of samples and the
> sampling rate be if I need the to detect the frequency every 1ms? Is
> there any other VI that does timing?