Our FCC test house is asking what the IF frequency is for the nRF51822
The IF is the difference between the receiving frequency and the LO. The LO is at (fRX+2MHz)*8/7. This gives:
fIF = fLO - fRX = (fRX + 2MHz)*8/7 - fRX = 1/7 fRX + 16/7
So at channel 2400MHz, the IF will be at 345.143MHz and at channel 2480MHz, the IF is at 356.571MHz.
