Re: [Discuss-gnuradio] Clock Sync Problems + Timestamp question

[Matt Ettus]

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