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Need suggestion on FSK receiver, carrier 1..500MHz, tone spacing ~2MHz, switching rate ~30kHz.

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ArrayCad

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I need an advice on FSK receiver solution, preferably with simple binary output, similar to SE564 (Fig.11). I do not have expertise to say if SE564 may be used for such wide channel bandwidth (2MHz). Currently I have IF output from downconverter, signal of interest is a simple frequency tone switching between two frequencies f1 and f2 with 30kHz rate. VCO tuning rage of downconverter provides arbitrary value for Fc between 1 MHz and 500 MHz.
f1 = Fc - 1 MHz
f2 = Fc +1 MHz
I've searched for various receiver / transceiver ICs, for example Si4355, but datasheet states maximum channel bandwidth is 850 kHz. From my understanding, for f2-f1=2MHz tone spacing I need channel bandwidth which is greater than 2000 kHz.
Thanks
 

danadakk

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Capture range certainly seems adequate, see attached.


Regards, Dana.
 

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  • NE564N.pdf
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  • 1972_Signetics_PLL_Applications.pdf
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  • AN1801.pdf
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biff44

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your data rate is 30 khz, but you want FM deviation of 2 mhz? what am i missing?
why not use a 100 KHz deviation, and go with the standard Nordic or TI chips?
 

ArrayCad

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danadakk, thank you
biff44, good question. I was puzzled by it too until discovered that 2 MHz is for phase interferometry at the transceiver side, to achieve acceptable balance between maximum unambiguous range and phase to range conversion with good resolution, and 32.768kHz for time synchronization between transceiver and multiple receivers.
 

biff44

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well the phase is in fact determined by the two independent "carriers" at 2 MHz apart.

but you need something to tell you when "zero phase" happens, i.e. a starting point in time with which to measure the phase difference as you move in distance. Otherwise if you do not keep track of time and the "zero time" starting event, you just have a jumble of ambiguities as you move over a big distance.

systems i have tried to do this with in the past have different spacings. maybe 100 KHz, then 2 MHz, then 10 MHz, in order to get different resolutions.
 

biff44

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BTW, you do probably realize that if you transmit two carrier tones, 2 mhz apart, the resulting waveform envelope will form a pattern that adds constructively, and subtracts destructively, at a period of 2 MHz. you can detect that envelope, and do some crude distance measuring with where the amplitude nulls are in time, without having to do a phase detection of the two individual carriers.
 

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