From: Robert L. <rob...@gm...> - 2014-08-05 07:11:36
|
<html><head></head><body><div style="font-family: Verdana;font-size: 12.0px;"><div> <div>Hi Balint,</div> <div>Thanks for the patch. I will have a look at it later.</div> <div>Let me explain the issue with the clock. Ettus designed the clock with a VCXO and a PLL. VCXO is, I think 0.5ppm, which would be good enough even for OpenBTS. But Ettus wants people to buy also a very expensive GPSDO, so to break the things for more demanding applications, like OpenBTS, they decided to put bias resistors on the control voltage pin of the VCXO, which will deliberately de-tune a good quality clock. You can figure out the hardware fix now.</div> <div>I do use kalibrate in order estimate the clock offset and believe me, I had about twenty B2x0 and none of them had an offset below 1kHz. And it drifts badly with temperature and power supply variations.</div> <div> </div> <div>For everyone who has a problems getting phones to work with B2x0, do what Balint says. Run kalibrate. You wanna see an offset below 100Hz, 200Hz is still ok, most phones will work if offset is below 500Hz, above that you will start having problems even with very "forgiving" phones, above 1kHz you need to take action on your hardware.</div> <div> </div> <div>(Balint I did notice your ettus.com email, and please really, really do not take this email personally. Ettus.com made me angry in the past with this "commercial policy", that I designed my own hardware for OpenBTS.)</div> <div> <div name="quote" style="margin:10px 5px 5px 10px; padding: 10px 0 10px 10px; border-left:2px solid #C3D9E5; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"> <div style="margin:0 0 10px 0;"><br/> <b>Betreff:</b> Re: [Openbts-discuss] Problem with OpenBTS 5.0.0 and B210</div> <div name="quoted-content"> <div> <div> <div> <div> <div> <div> <div>Hi Robert,<br/> </div> I use my B210 with OpenBTS all the time. It's true that there will inevitably be some frequency offset without an external reference that will result in certain phones not camping, or call drop outs - this has always been an issue as I'm sure you're aware.</div> </div> </div> </div> </div> </div> </div> </div> </div> </div></div></body></html> |