Hi,
I have to transmit data modulated with 250Hz carrier and bit time of 12ms (3 period of carrier). Obviously i need to demodulate that message on receiver side.

The problem is that on the transmission channel 60Hz and 180Hz signals are present. So that two frequencies could be added to the transmitted signal @ 250Hz.

Now i don't know witch kind of modulation/demodulation method is the best suitable for my purpose and if i use a classical one (ask or bpsk) is there a technique to filter out undesired frequencies?

Thanks let me know.

 

Why not just use a high-pass filter to remove anything below, say, 200 Hz? Or a notch filter centered at 250Hz?

 

why not just plain psk? run the carrier through one side of an exclusive or gate and the data through the other. out comes psk. xor gate inverts when data =1 and dosnt when data =0. simple demod too.

 

Where is the 60Hz and 180Hz coming from? What is the transport medium?