DW1000 AGC Measurement

Dear Sirs,
I have a question about the AGC measurement. The user manual of DW1000 shows that it is possible to measure the background noise level in order to choose the less noisy channel. I tried to make this measure recursively for my own purposes but the values I got (using the user manual formula) were very different between them. The pseudocode is the following:

  1. enable agc measurement,

  2. enable rx ,

  3. wait 100 us,

  4. read the value from the sub register: Sub-Register 0x23:1E – AGC_STAT1,

  5. apply the formula (EDV2 −40) ×10^EDG1×𝑆𝑐ℎ, where 𝑆𝑐ℎ in my case is 1.3335,

  6. repeat from 1) to 5) each 2 seconds.

Typical values I get for EDV2 when i don’t apply any disturb are from 6 to10. If I apply a disturb in that channel the values I get from EDV2 goes from 4 to10. Why the values are not stable?
Thanks in advance.