Forum: GNU Radio B200 clock calibration

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F1885cad1acb7793978438a46ea62cb8?d=identicon&s=25 Robert Light (Guest)
on 2014-05-14 12:14
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I try to get B200 to work with OpenBTS and I see some frequency offset
in the internal reference clock.
Does anyone know if the numbers I get from kalibrate, could cause phones
not to be able to register to OpenBTS?
 What is the quickest and the cheapest way fix a problem with a clock? I
think B200 has TCVCXO, so is there a way to write some tuning voltage
offset to
 correct the frequency? Do a clock calibration?  Does anyone know the
exact part nr of TCVCXO
 mounted in B200?

 UHD Warning:
 The hardware does not support the requested RX sample rate:
 Target sample rate: 0.270833 MSps
 Actual sample rate: 0.271186 MSps

 kal: Scanning for GSM-900 base stations.
 chan: 19 (938.8MHz + 1.915kHz) power: 2812.45
 chan: 26 (940.2MHz + 1.900kHz) power: 14595.33
 chan: 33 (941.6MHz + 1.913kHz) power: 18358.13
 chan: 58 (946.6MHz + 1.930kHz) power: 9563.79
 chan: 114 (957.8MHz + 1.957kHz) power: 1872.65

 Using GSM-900 channel 19 (938.8MHz)
 average [min, max] (range, stddev)
 + 1.896kHz [1855, 1943] (88, 19.746572)
 overruns: 0
 not found: 92
B4ffbc711addde4c649b1ed526df6157?d=identicon&s=25 Martin Braun (Guest)
on 2014-05-14 12:17
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On 14.05.2014 12:12, Robert Light wrote:
>   Actual sample rate: 0.271186 MSps

as long as you see this warning, you'll get offsets. I don't know where
or how kal sets up the master clock, but you should put in a
master_clock_rate=13e6 somewhere in there.

0817fa933c74eec9b3fcf3a04e16f418?d=identicon&s=25 Sylvain Munaut (Guest)
on 2014-05-14 14:33
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> I
> think B200 has TCVCXO, so is there a way to write some tuning voltage offset to
>  correct the frequency?

There is no way to trim the TCVCXO manually. It's included in the loop
of a PLL for external locking but you can't control it directly.

It seems that manual control was considered because adding a resitor
can connect the control line to an aux DAC of the ADI, however it
seems that the voltage might not be compatible and so you'd need
external amplification to drive it. (that's from memory, might be
worth rechecking schematics and specs)


Ddb503356cb90b0c95e52700445ef749?d=identicon&s=25 Tom Tsou (Guest)
on 2014-05-14 17:45
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On Wed, May 14, 2014 at 6:16 AM, Martin Braun <>
> master_clock_rate=13e6 somewhere in there.
In this particular case, it's actually not very important. Kal is
basically performing a tone search and the sample rate used for
internal calculations is the rate returned by UHD. The sample rate can
be almost any value.

2 kHz offset is within tolerance for 1900 MHz. Locking to a stable 10
MHz reference, generally an OCXO or GPSDO, is the recommended

558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus D. Leech (Guest)
on 2014-05-14 17:49
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On 05/14/2014 11:44 AM, Tom Tsou wrote:
>> master_clock_rate=13e6 somewhere in there.
> _______________________________________________
> Discuss-gnuradio mailing list
The on-board clock on the B200 is good to about 2PPM, so 2kHz in 1900Mhz
is just about right.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
558c40b97bd1af8d912424757714bda9?d=identicon&s=25 Marcus Leech (Guest)
on 2014-05-16 10:27
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