Hello Harald,

On Fri, 17 Apr 2009 10:17:13 +0200, "Harald Welte" laforge@gnumonks.org wrote:

Dieter, what I just found out is that the LI object has a user-configurable setting, where we can force it to be stand alone or locked to the E1.

You mean the "PLL synchonisation mode" attribute which is set to "locked mode" ? I am not sure if we can change it for our version of the BS-11. As far as I understand the documentation, this is a setting which is only available with the CCU ("Combo Card Unit", the universal interface which also allows to use a standard ISDN line). The documentation mentions at one place that for the CCU variant they use an oven controlled oscillator which fulfilles the GSM clock stability requirements even without being snchronized to the E1 line.

But we should of course try it.

We could add this setting to the bs11_config program so people can try if their E1 clock or their [10 years uncalibrated] BS11 internal oscillator is better.

What do you think?

Yes, why not try it. Probably the result is similar to disabling the master clock of the HFC-E1 card, this way the BS-11 clock determines the E1 clock (the HFC-E1 card synchronizes to the trasmitter E1 clock of the BS-11 and the BS-11 locks to the transmitter clock of the HFC-E1 which is determined by the BS-11). Surely the cleaner way is to adjust the clock setting in the BS-11 (if this settings works for our BS-11 variant).

I'm quite sure there must be an option to do this externally. The internal oscillator must be calibrated every two years, and I'm sure they do this without opening the case (in the field...)

Its possible to calibrate the PLL without opening the case. The attribute is protected by some checksum, I have not looked at the details. And "officially" out LMT version should not even allow to see the calibration dialog ;-) The problem for me is how to measure the clock without opening the case. I can measure an unmodulated carrier very accurate if it is within the 10 MHz to 1 GHz range (the HP 8922 is accurate enough to do this). However I don't have the equippment to measure the modulated and pulsed signal of the BS-11. Maybe there is some hidden setting to send just the unmodulated carrier, but I have not yet found anything in this direction.

Another problem is that changing the calibration requires a restart of the BS-11 (at least I only saw any effect when I restarted). Additionally when you query the calibration, you get the "PLL Set Value" and the "PLL Work Value", the "Set Value" seems to be used when starting up and the "Work Value" changes, most certainly locking to an external clock also influences it. I did not find anything in the documentation, actually those settings are not indended for the end user, just the factory.

Best regards, Dieter