That's true, but their are two frequency synthesizers (ADF4360-0 on my flex2400) on each flex daughter card (one for TX and one for RX -- or more generically one for each sub-subdevice). On the basic daughter cards (which only have one sub-subdevice) there is only one synthesizer, but you need a second daughter card to complete the path (one for TX, one for RX).
Ultimately, this is not a software (firmware fix) or sampling problem (use the same ADC or supply sync signal). This is a physics problem that results from using two independent oscaillators that are not phase locked to each other. Resultingly, you need a hardware fix to achieve coherence. That said, this is a problem that will manifest itself in your real-world application and is not easy to solve except by phase locking the oscillators through a cable (which doesn't work well for anything, except really short separation distances). What is your ultimate application? Cheers, -Jonathan On Sun, Jun 22, 2008 at 3:58 AM, wolfgang buesser <[EMAIL PROTECTED]> wrote: > > Just to make sure: > > I am using LF RX/TX-boards. > TX and RX are on the subdev (thus using the same AD9862) > > Thanks > Wolfgang > > > > Jonathan Friedman-2 wrote: >> >> Unless I misunderstand what you are doing, what you are describing is >> the coherence error of the system. The long-answer made short is "no". >> You have to calibrate it out or otherwise live with it. The TX and RX >> paths of the USRP are derived from separate hardware local oscillators >> so there will always be an unknown phase error between them. What's >> worse is that it will vary slowly and dynamically as temperature and >> voltage change during system operation. >> >> Cheers, >> -Jonathan >> >> On Sun, Jun 22, 2008 at 2:42 AM, wolfgang buesser >> <[EMAIL PROTECTED]> wrote: >>> >>> Hi, >>> >>> Iam using >>> gr.sig_source_s (self.usb_freq (), gr.GR_CONST_WAVE, 0, 0, 0) >>> to generate a carrier and >>> usrp.source_c(nchan=2,decim_rate=self.interp) to resample it at the >>> same >>> frequency. >>> >>> I get what I expect: 2 complex numbers which are pretty constant. But >>> with >>> every restart >>> of the program the phase changes (apparently by the same amount for both >>> channels). The >>> amplitude does not vary much from run to run. >>> >>> It seems to me, that the phase relation between the interpolator in the >>> TX >>> and the decimator in >>> the RX changes with every restart. >>> >>> Is there a way to "reset" the interpolator/decimator so that I get the >>> same >>> reading for every start >>> (as long as I don't change frequencies) ? >>> >>> Thank's >>> Wolfgang >>> -- >>> View this message in context: >>> http://www.nabble.com/unknown-phase-relation-between-rx-and-tx-tp18052839p18052839.html >>> Sent from the GnuRadio mailing list archive at Nabble.com. >>> >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org >>> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> > > -- > View this message in context: > http://www.nabble.com/unknown-phase-relation-between-rx-and-tx-tp18052839p18053437.html > Sent from the GnuRadio mailing list archive at Nabble.com. > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
