Significance of calibration

[Das Signal]

On Mon, May 11, 2015 at 05:24:36PM +0000, Spacefalcon the Outlaw wrote:

> I remember DS saying that he has some RF test equipment that could be
> used for calibration - DS, perhaps you could give us your thoughts on
> whether or not the setup you have could be used to perform calibration
> procedures as described above for GSM devices of our own make?

Hi SF,

You are absolutely correct, I do have an USRP B100 that I use in tandem
with OpenBTS; it works very well, and I can send SMS, place phone calls,
and even make IP connections over GPRS. The built-in clock is rather
precise, I measured about 300 Hz deviation at 940 MHz using kalibrate,
this is almost good enough in theory for GSM which requires 0.5 ppm and
300 / 940e6 = 0.319e-6 = 0.319 ppm, so largely within spec and in theory
could be used to calibrate the VCXO.

Calibrating rx power level could be a little harder since I lack an
absolute power reference, from say an Agilent (Keysight) or some other
signal generator; and the USRP does not provide an absolute power ref.
However I could use existing calibration values from a working phone
as a reference for rx, and possibly tx as well.

--DS