To eliminate the IMD
Roger,
Not really IMD. A characteristic of sampling receivers.
Softrocks and many other SDRs will respond to signals at odd multiples of the tuned frequency. One sample in every three, or five etc. Lower sensitivity but still significant.
This was used by Tony in some of the crystalled "Lites" using a crystal 1/3 of the frequency.
It is even used in modern SDRs to extend the range beyond what might be expected from the actual sample rate.
LPFs, BPFs are used to limit the input range to what is required.
73 Alan G4ZFQ
