Hi Josh and others,
I have some more questions related to DUC/DDC cordic, USRP tuning process:
1) When an eob tag is issued, the DUC phase accumulator on transmit DSP chain is reset. What about the DDC phase accumulator on receive DSP chain? Does it reset at well? I am asking because I have seen that the receive DSP chain and transmit DSP chain apply independent freq corrections in order to tune to the desired center RX and TX frequencies. In other words, is there any relation/binding between the DUC cordic and DDC cordic? I hope two separate/independent phase accumulators are used for DDC and DUC cordic's but I want to verify.
2) What is the tuning granularity of RF front end? I can see from USRP FAQ on gnuradio.org that it is 4MHz for RFX
boards.
http://gnuradio.org/redmine/projects/gnuradio/wiki/UsrpFAQDBoards#How-is-RF-tuning-accomplished-in-daughterboards
Is step size dependent on the daughterboard, mother board or both? I am asking because when I set my USRP N200 to transmit at say 892MHz, I observe the below values:
Actual RF freq: 892857142.847963 Hz
Actual DUC DSP freq: -
857142.847963 HzWhat does an RF frequency of
892857142.847963 tell about the step size of RF front-end (which is RFX900)?
Thanks in anticipation,
Yu.