The waveform of yours consists of 2 frequencys, that is, a carrier frequency and a signal frequency, and the signal frequency usually consists of a multiple-frequency waveform, look at AM Radio Signallings. If you want to lower down such a frequency, the best way is lower down it when you have not mix the 2 signals together. And what's more, a Doppler Effect could change such a wave frequency: As the vilocity from the receiver and boardcastor is vv(the One vertical to the line of reciever and boardcastor) and vh(the One horizotal to the line of receiver and boardcastor). And there is a formula on such cases --
Frequency(switched) = {(1 + vh/c) + [1 + (vv/c)^2]^(1/2) - 1}*Frequency(original).
Note:
If the vv leaves the boardcastor, vv is positive and if vv reaches the boardcastor, vv is negative!!