FSK demodulation of 750 kHz mark and 250 kHz space

Hello, we are trying to make a FSK demodulator of intermediate frequency 500 kHz having mark frequency of 750 kHz and space frequency of 250 kHz.

We have tried using an LM 565 PLL to demodulate these modulation frequencies. When we tried the values we get for the sample circuit in the datasheet there were no results.

The demodulating circuits build using this component are usually operating at 2025 Hz - 2225 Hz.

Do you think these frequencies are too high to demodulate with this component? If this is not the case can you suggest any other component or schematics?

Thanks for the help in advance.

The datasheet says the maximum operating frequency is 300kHz (min.) so that circuit will not reliably detect a 750kHz signal. It's also an obsolete device.

Edit: If you used the sample circuit, which is designed for 2025Hz-2225Hz, how did you expect it could operate at 500kHz??

You might be able to use a CD4046 PLL which will go over 1MHz with a 10V supply.

Thank you for the suggestion. It seems like the component really can handle inputs of that frequency. I hope I can it in the local electronics shops.

However, just to be exhaustive on the topic. The most basic operation that we can perform is to check if the incoming frequency is higher than 500 kHz or not. Is using a PLL the most easy/cost effective way to perform this operation.

I thank you for your quick reply again.

impalor said:

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However, just to be exhaustive on the topic. The most basic operation that we can perform is to check if the incoming frequency is higher than 500 kHz or not. Is using a PLL the most easy/cost effective way to perform this operation.

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It's basically a one-chip solution using an inexpensive IC. Don't think there's any easier or cheaper way.

Also available is the 74HC4046 which is a high speed version that will operate up to 12MHz with a 5V supply.

Thanks a lot for your help. I will search for them in the component shop tomorrow.