Max NCO, relation to sampling rate, and NCO effect


#1

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.