Hi, I am using the same clock reference to both b100 devices. the clock reference is XL microwave model 500, it is rubidium based, and it has multiple outputs. since I am connecting it to both B100s (the actual same clock reference) I was expecting that the Rx and Tx frequencies will be exactly the same. but I still got 570Hz difference. when I did not invoke the tune request command, the Rx was distorted (the Tx was fine, I tested it with a spectrum analyzer)
Regards, Guy On Mon, Jun 3, 2013 at 10:19 PM, Marcus Leech <[email protected]> wrote: > Tune request is independant of external clocking--that's an orthogonal > property of an instantiated device object. > > On TX the LO will be tuned to whatever you've set as the LO offset, so any > LO leakage will appear there, but your signal will be where it's supposed > to be. > > 570hz/915e6Hz is a residual frequency error of 0.6PPM. > > What are you using for your external reference? The B100 clock itself is > good to about +/- 2.5PPM, so 0.6PPM sounds like it's locking to an external > reference, or you're just "lucky". > > uhd.tune_request() is used to request a tuning with more-complete control > over the RF and DSP tuning aspects: > > http://files.ettus.com/uhd_docs/manual/html/general.html#tuning-notes > > I'd suggest you familiarize yourself with the entire documentation tree > that's online: > > http://ettus-apps.sourcerepo.com/redmine/ettus/projects/uhd/wiki > > > > > on Jun 03, 2013, *Guy Holtzman* <[email protected]> wrote: > > LED E is always on, even when I disconnect the external source > > I used this command on the Tx: > uhd.tune_request(915000000) > > and this command on the Rx: > uhd.tune_request(915000000,10e6) > > the freq is now very stable > but there is a constant shift of 570 Hz between Rx and Tx > > another strange thing happened: > when I used the command > uhd.tune_request(915000000,10e6) > on the Tx, the USRP transmitted with a shift of 10 MHz (minus a few 100s > Hertz) > > is this ok? > > what can I do to solve the constant shift of 570Hz > what is the uhd.tune_request command and how can I use it when configured > to external clock? > Thanks, Guy > > > On Mon, Jun 3, 2013 at 3:39 PM, Marcus D. Leech <[email protected]> wrote: > >> I Checked the levels with the clock connected to the USRP ( and without) >>> The levels are fine ( about 600 mV rms on the scope) >>> additionally, I disconnected it from the load (USRP) to see if the level >>> changed. and they did (proving the cables are connected to a load). >>> >>> the problem remains, >>> is there a command that could check if the USRP is locked to the >>> external clock? >>> what is the best way to debug this and to find the root cause? >>> >>> Thanks for your help, >>> Guy >>> >>> You can use "test_pps_input" which is one of the UHD examples. >> >> Also, LED 'E' tells you whether the clock is locked to the external >> reference. >> >> >> >> >> >> -- >> Marcus Leech >> Principal Investigator >> Shirleys Bay Radio Astronomy Consortium >> http://www.sbrac.org >> >
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