It all depends on the dynamic range of the receiver and the DSP. If the
strong signals passing through the receiver but rejected by the external
DSP cause the receiver gain to drop so low as to loose the desired
signal in the receiver or the digitizing noise, then the DSP can't
accomplish the processing. There is a fundamental limit on the dynamic
range of the DSP, that of the A/D. One bit of delta doesn't make for a
good process, and if the A/D is under 24 bits (which is why the TenTec
DSP receivers use a 14 KHZ last IF, the good 24 bit A/D that work at 9
MHZ cost more than Tentec would like to sell the radio for) then the
weaker signals get lost in digitizing noise. Then if the DSP is less
than 24 bits more gets lost. Its a matter of both analog and digital
dynamic range.
73, Jerry, K0CQ
--
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
|