If you understand FM - you will realize that FM has many side bands - hence the center frequency of your whole house transmitter is 88.1 - but it has harmonics on other frequencies on either side of 88.1 - this is how FM works!

All signals reduce at the square of the distance away....

You either need to move your transmit or your receive antenna - have some sort of separation between the two or use a filter.

http://dsp.stackexchange.com/questio...d-in-am-and-fm