Max NCO, relation to sampling rate, and NCO effect


Hi all,

It seems in RX, in single channel, the NCO up and downconvert is limited by the sampling rate as follow

  • must always be < 80MHz
  • must be < sampling rate * 16

For TX in single channel it’s the same, except it’s <= sampling rate * 16

In dual channel, it seems that in RX if the sampling rate is

  • >= 40MS/s, then the NCO must be <= sampling rate
  • < 40MS/s, then it’s back to < sampling rate * 16 as long as it’s < 80MHz

In dual channel in TX it’s the same except the conditions are > 40MS/s and <= 40MS/s.

Is this how the NCO is programmed?

Also, what is the impact of the NCO with regard to the sent/received signals? Should I try to keep it to a minimum? Does that minimum depend on the sampling rate?

Eg in dual RX, I use 55MS/s at 2450MHz with NCO +/- 23MHz to listen on 101MHz with some overlap in the middle.