FSK Transmitter and Receiver

[Aldous Mantiza]

HI! I'm a new member
I am designing an FSK transmitter. But my digital input is a manchester encoded. Would that affect my circuit design? Or any kind of digital input can be used and my transmitter will be the same. Thanks

 

[chuckey]

If you are using a binary FSK (two frequencies or phases) no problems.
Frank

 

[biff44]

you actually WANT Manchester encoding on FSK, otherwise your apparent center frequency will drift. For instance, if your header data is 000000000010 then data, in the first 10 bits, your center frequency will drift due to the PLL you probably have, so that F0 starts to look like (F1-F0)/2. then when the "1" comes, the VCO will overshoot too high over F1.

the result....you might not detect the header at all.

Manchester coding would not let so many of the same bit be transmitted in a row.

 

[Aldous Mantiza]

I found an FSK transmitter with an ASCII input.
https://www.assignmentpoint.com/science/eee/design-and-implementation-of-a-frequency.html

Can I use the same circuit(modulator part) if my input is Manchester encoded?
Thanks.

 

[chuckey]

This chip sems to be designed for PSK. So the local oscillator locks to the incoming frequency and the outputs from the mixers represent the phase deviation.. I and Q being 90 degrees different and represent 1s and 0s. If you feed it with FSK, will the local oscillator lock up to the mean frequency? and if it does the outputs from the I and Q mixers will be two sine waves of half the frequency shift but 90 degrees out of phase. I am not sure if you could then make anything meaningful from these.* A better way would be to have a fast PLL lock up, so the local oscillator "jumps" from frequency to frequency as the FSK comes in and detect the change in the PLL representing hi/lo frequencies.
Perhaps you should read the datasheet more thoroughly then I did!
Frank
* Afterthought :- If you can arrange a sampling pulse based on the zero crossing of one of the sine waves then sampling the other would give you a +/- output as a hi/lo frequency detector. There must be an easier way!!!