FSK modulation / demodulation

fsk modulator demodulator

Hi,

I had xr2206 as fsk modulator and xr2211 as fsk demodulator. My logic 0 = 2kHz and logic 1 = 5kHz. I had already put all the components base on my design.

But there are some doubts.

1. How should the modulator and demodulator being tested properly? Is it connecting the xr2206 output to xr2211 input through a wire or connecting wirelessly? I had use a function generator to test the demodulation and it works fine. But is there any way to test both the circuit wirelessly?

2. Is the output of xr2211 demodulator an invert of the TTL logic? For frequency < 3.2kHz i get HIGH (4.75V) and for frequency > 3.2kHz i get LOW (0.045V). By right i should obtained HIGH for freq > 3.2kHz and LOW for freq < 3.2kHz.

Please advice me. Thanks.

Regards,
cwt

xr2206 modulator

Hi Use an IR LED and an IR transistor as receiving device.

Paul.

fsk modulator & demodulator

Hi,

1. When I feed in the FSK output from the modulator to the demodulator input (through a wire), the TTL output voltage is both HIGH at lower frequency (2kHz) and higher frequency (5kHz). But when i use the function generator to feed into the demodulator with the same frequencies, the output voltage is LOW at 5kHz and HIGH at 2kHz. Can anyone explain why this is happening?

2. Is the modulator suppose to give an invertion of the voltage with respect to the FSK frequencies?

3. Just to confirm, do the baud rate affect the design criteria?

Regards,
cwt

xr2211 demodulator

Hi,

I manage to solve the problems. However, there is another problem arises. Is there anyone who built and tested the xr2206 with xr2211? I would like to hear opinions from you.

When i use the 600Hz output of function generator (+2.5V and -2.5V) to drive the xr2206, the FSK output is biased at certain positive voltage level and the output will be feed into the xr2211. The output from the xr2211 is a demodulated signal with +5V and 0V.

When i use the PIC to send a 600Hz squarewave signal (+5V and 0V) to the xr2206, the FSK output is biased at 0V and the xr2211 output is +2.5V and -2.5V.

For my case i want to send a 0V-5V signal and retrieve back the signal in the form of 0V and 5V. Is there circuit parameters i can do to achieve that?

Thanks.

Regards,
cwt

xr2211 an

Put a capacitor in series with the line between the two units. Then you can use two resistors in a voltage divider configuration to set the DC level into the receiver to be what you want.

fsk modulation-demodulation

The demodulator input has a 0.1uF capacitor.

I need some verification on the FSK demodulator.

Is it the xr2211 demodulator should give an 0V to 5V output if the input to the xr2206 modulator is a split voltage signal (+V and -V)? (See figure, yellow = input, blue = output)

Or is it the xr2211 demodulator give an +V and -V output if the input to xr2206 is a 0V to 5V supply?

Or is it the xr2211 demodulator only gives 0V to 5V output regardless of the nature of input signal.

Previously, i am able to obtained the 0V to 5V signal as shown in the figure. But now i cant obtained that (even with same circuit configuration). I need someone who has deal with xr2206 and xr2211 to verify with me.

xr2211 spoilt?

fsk modulator demodulator using pic

Hi all,

I manage to solve this. It is not because of my circuit problem. Its due to the oscilloscope setting.
It should set to dc coupling instead of the ac coupling. What a problem. LOL

Regards,
cwt

so how did you connect the output of the modulator to the input of the demodulator? did you connect it directly through wires? or did you use anything(eg.capacitors,resistor,ics,etc)?