Ah! The 10MHz was coming out the back of the siggen so would have been locked to the same reference.
Thanks for your help Doug/Matt -- next time I'll stop and think through my test setup! Cheers, Tim On Tue, Oct 20, 2009 at 6:16 PM, Matt Ettus <m...@ettus.com> wrote: > Tim Pearce wrote: > >> >> >> >> There is no frequency which can be received by both the BasicRX and >> the DBSRX. What frequency are you putting in? What frequency are >> you telling the USRP2s to tune to? >> >> Matt >> >> >> Hi, >> >> Sorry I probably confused things by mentioning the BasicRX >> >> DBSRX is the only receiver we have 2 of at the moment so I was testing >> with a 2 GHz Sine wave, tuning the USRP2 to 2GHz and setting decim to 50. >> >> The problem was seen on both usrp2's after enabling the 10MHz ref lock. >> > > > When you lock the reference of the USRP2, it will be exactly on 2 GHz. So > if you put in a 2 GHz sine wave which is also locked to the same reference > or locked to something very close, it will also be at exactly 2 GHz. Thus, > when it is downconverted to baseband, it will be at DC, and will be removed > by the DC offset correction. Everything is functioning exactly as it > should. > > > Before enabling the ref lock the sine wave appeared on the oscilloscope as >> expected. >> > > That is because without the ref lock you will have some frequency error, > and the signal won't be on exactly 2 GHz. > > >> I tried one USRP2 with the BasicRX just to check the same problem was >> appearing -- a 25MHz and 150MHz signal were tested (same decim and tuning to >> the frequency the sig gen is generating on). Both frequencies looked correct >> on the scope sink until the program was run with the clock locked to the >> reference in. - the symptom was slightly different (appearing as a DC signal >> rather than noise) which is why I mentioned. >> > > The BasicRX has no DC offset correction, so you will see a DC level, which > is exactly what you are asking for. > > I think that what you really want is to tune the USRP2 and the sig gen to > different frequencies. > > Matt >
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