Problem with plugging FSK modem to FM TX

[ex4]

I'm building FSK modem with frequency of 15kHz and 25kHz on 4800bps data rates. I'm using it with my FM TX and i got some major problems:
when i test the modem with loopback cable, it works great, but when i plugged it into my TX it began to decrease and the data is corrupted approximately 33% from the total transmitted data. I've decrease the baud rate down to 1200bps and it still got that much error
Got any idea why and how am i suppossed to fix it?should i change to ASK for better simplicity of cicuitry and error manmgement???

 

[flatulent]

Re: FSK & FM

One thing to do is use an oscilloscope to examine the output of the FM detector. Also the amplifier stages that follow. I suspect that your FM transmitter and receiver are designed for passband signals such as voice and does not go down to DC in the modulation.

 

[hermin]

FSK & FM

You may want to try IC's from TI or microhip or maxim-ic. They have a lot of IC's which operate within you specifications...

 

[ex4]

Re: FSK & FM

i've examine the output of fm rx with oscilloscope and it really good
or should i decrease the frequency of the FSK modulator, let's say to audio frequency. I plugged the modem one to my microcontroller and the one to my computer. The computer act as server and the microcontroller act as client. When i send command to the micro, the micro is acknowledge with very good. but when my micro sends back to my computer, the data is damaged
gt any suggestion???
what this means : does not go down to DC in the modulation?

 

[armsgroup]

FSK & FM

Hi
The loopback test will not examin the channel effect on your data i think the error you have is from the channel you can try to increase the power transmitted it will increase the SNR that will reduse error

 

[lincoln123]

Re: FSK & FM

Try effective PLL to fix error and simulators