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Discussion and technical support related to USRP, UHD, RFNoC

USP B205mini-i with external clock using Leo Bodnar GPSDO on srsRan eNodeB

Karsten Ohme

Mon, Apr 11, 2022 4:14 PM

Hi,

I have purchased a Precision GPS Reference Clock
(http://www.leobodnar.com/shop/index.php?main_page=index&cPath=107
) but have troubles to make it work with an Ettus USRP B205mini-i.

I assume everything is configured correctly, 10 MHz, square wave input,
I have a GPS signal, 3.3 Volt, 13.3 dB attenuation, the USRP is
connected on output 1 on the Leo Bodnar GPSDO, but neither on UHD
version 3.15.0 nor on version 4 the external clock is used. I configured
the USRP to use the external clock with "device_args = clock=external"
in srsRAN eNodeB but I get as error:

Could not lock reference clock source. Sensor: ref_locked=false

I could not find any useful information about a reason for this error.
Could you please provide some ideas about possible reasons for this
behavior?

Regards,

Karsten

Hi, I have purchased a Precision GPS Reference Clock (http://www.leobodnar.com/shop/index.php?main_page=index&cPath=107 ) but have troubles to make it work with an Ettus USRP B205mini-i. I assume everything is configured correctly, 10 MHz, square wave input, I have a GPS signal, 3.3 Volt, 13.3 dB attenuation, the USRP is connected on output 1 on the Leo Bodnar GPSDO, but neither on UHD version 3.15.0 nor on version 4 the external clock is used. I configured the USRP to use the external clock with "device_args = clock=external" in srsRAN eNodeB but I get as error: Could not lock reference clock source. Sensor: ref_locked=false I could not find any useful information about a reason for this error. Could you please provide some ideas about possible reasons for this behavior? Regards, Karsten

Marcus D. Leech

Thu, Apr 14, 2022 3:44 AM

On 2022-04-11 12:14, Karsten Ohme wrote:

Hi,

I have purchased a Precision GPS Reference Clock
(http://www.leobodnar.com/shop/index.php?main_page=index&cPath=107
) but have troubles to make it work with an Ettus USRP B205mini-i.

Could not lock reference clock source. Sensor: ref_locked=false

I could not find any useful information about a reason for this error.
Could you please provide some ideas about possible reasons for this
behavior?

Regards,

Karsten

Not sure how srsRAN maps the configuration file it uses to actual UHD
calls, but a "set_clock_source("external")" should work just fine
according to
experiments I've done in the past.

Be warned that the clock "servo" in the mini series doesn't act like a
smooth analog PLL, so the close-in phase-noise will be poor.

I apologize for the delay in responding--my e-mail client has taken to
marking a lot of usrp-users traffic as "spam", and I'm not sure why.

On 2022-04-11 12:14, Karsten Ohme wrote: > Hi, > > > I have purchased a Precision GPS Reference Clock > (http://www.leobodnar.com/shop/index.php?main_page=index&cPath=107 > ) but have troubles to make it work with an Ettus USRP B205mini-i. > > I assume everything is configured correctly, 10 MHz, square wave input, > I have a GPS signal, 3.3 Volt, 13.3 dB attenuation, the USRP is > connected on output 1 on the Leo Bodnar GPSDO, but neither on UHD > version 3.15.0 nor on version 4 the external clock is used. I configured > the USRP to use the external clock with "device_args = clock=external" > in srsRAN eNodeB but I get as error: > > > Could not lock reference clock source. Sensor: ref_locked=false > > > I could not find any useful information about a reason for this error. > Could you please provide some ideas about possible reasons for this > behavior? > > > Regards, > > Karsten > Not sure how srsRAN maps the configuration file it uses to actual UHD calls, but a "set_clock_source("external")" should work just fine according to experiments I've done in the past. Be warned that the clock "servo" in the mini series doesn't act like a smooth analog PLL, so the close-in phase-noise will be poor. I apologize for the delay in responding--my e-mail client has taken to marking a lot of usrp-users traffic as "spam", and I'm not sure why.