A RF signal of 7.0005MHz, 7.0006MHz, 7.0007MHz, 7.0008MHz, 7.0009MHz, and 7.0010MHz, each 5 second duration, is down converted to audio frequency with the LO of 7MHz.
The audio signal is fed into a PC and FFTed using Audacity.
This is when the RF signal is fixed to 7.0005MHz.