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Mario Benitez
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Simple FSK signal generation.

Hello, I am trying to generate a simple FSK signal. Basically I have two Frequency Synthesizers generating (individually) a square wave each based on a set of given parameters. One represents zeroes and the other represents ones. On the other hand I have a third Frequency Synthesizer which represents my data rate of codes that need to be sent. Each code is a 4 bit code that is rotational immune. To generate the FSK signal I just simply have to choose between the zeroes and ones based on what the bit code is. The bit code functions as a gate to transmit either ones or zeroes every so often (based on the third Freq. Synth). I have been able to generate all 3 Frequency Synthesizer, but I am having a lot of trouble creating the gate that determines what to transmit. The Frequency Synthesizers run on my FPGA module and they output a square wave to the Analog Output in my CompactRIO device using the Square Wave Generator  VI. Actually most of my code was taken from one of the Labview examples (Square Wave Generation).  Maybe you can suggest something. Thanks for the help Mario  
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Christian_L
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Re: Simple FSK signal generation.

Use the Select function to route one or the other of the two square waves to the output. The center input (Boolean) to the Select will be your data stream. 
Christian Loew, CLA
Principal Systems Engineer, National Instruments
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Mario Benitez
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Re: Simple FSK signal generation.

Hello Christian,

 

Thank you very much for your reply. I have tried using the select input. The problem that I see is that when I do that, them both Square Wave Generators use the same parameters (frequency, phase, etc), thus I see no difference in my output wave. Note that both Square Wave Generator VIs live under the same loop and both are using Outside Single Cycle Timed Loop as the Execution Mode.

 

I am not quite sure what I am missing, I hope you can help.

 

Thanks for the help in advanced.

 

Mario

 

 

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Christian_L
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Re: Simple FSK signal generation.

A FSK signal is based on the premise that you represent zero's and one's in your data with two different frequency signals. So in your case your two Square Wave Generators need to have different frequencies, most likely multiples of one another in order to maintain phase continuity in your output signal.

 

One common example of a FSK signal is the analog modem used by computers and fax machines. The chirping you hear when a fax or old time modem connects is the two different frequencies of the analog FSK signal.

 

A picture of a FSK signal based on binary data is shown in Figure 5 of the following appplication note.

 

http://zone.ni.com/devzone/cda/tut/p/id/3253

Christian Loew, CLA
Principal Systems Engineer, National Instruments
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ut perg
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Re: Simple FSK signal generation.

I got the modulator part to work.

 

But can you help with the demodulator portion.

 

I am changing the myDAQ ASK demo

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ut perg
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JJFang10
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Re: Simple FSK signal generation.

Hi, Do you know which chips that can store FSK signal - Bellcore 202, Caller ID signal (only 0 and 1).

 

Thanks

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Christian_L
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Re: Simple FSK signal generation.

JJFang10,

 

The example discussed in this thread is used to generate a FSK signal using NI HW. It does not use any thrid party components, and we do not have experience using third party HW for this purpose.

 

If you are looking for a Bellcore 202 decoder I would suggest searching using Google and contacting vendors that supply these types of components.

Christian Loew, CLA
Principal Systems Engineer, National Instruments
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