[USRP-users] Broken gpsdo or bad antenna?

Dario Lombardo dario.lombardo.ml at gmail.com
Wed Jun 20 04:06:42 EDT 2012


Hi Nick
That's a good point, I didn't think about it.
So, my setup now is as follows:
- gpsdo has just 1 connection to the motherboard, the power supply
- 10 MHz and pps sma cables are connected to the front panel
- J510 jumper is in position 1-2
- eeprom gpsdo is set to "none"

That's the output from kal, with and without -x switch:

$ ./kal -c 37
linux; GNU C++ version 4.5.1 20100924 (Red Hat 4.5.1-4); Boost_104400;
UHD_003.004.002-128-g12f7a5c9

-- Opening a USRP2/N-Series device...
-- Current recv frame size: 1472 bytes
-- Current send frame size: 1472 bytes

UHD Warning:
    The hardware does not support the requested RX sample rate:
    Target sample rate: 0.270833 MSps
    Actual sample rate: 0.271739 MSps
kal: Calculating clock frequency offset.
Using GSM-900 channel 37 (942.4MHz)
average [min, max] (range, stddev)
+ 207Hz [198, 216] (18, 4.685140)
overruns: 0
not found: 0

$ ./kal -c 37 -x
linux; GNU C++ version 4.5.1 20100924 (Red Hat 4.5.1-4); Boost_104400;
UHD_003.004.002-128-g12f7a5c9

-- Opening a USRP2/N-Series device...
-- Current recv frame size: 1472 bytes
-- Current send frame size: 1472 bytes

UHD Warning:
    The hardware does not support the requested RX sample rate:
    Target sample rate: 0.270833 MSps
    Actual sample rate: 0.271739 MSps
kal: Calculating clock frequency offset.
Using GSM-900 channel 37 (942.4MHz)
average [min, max] (range, stddev)
- 20.648kHz [-20736, -20565] (171, 49.960464)
overruns: 0
not found: 0

That's what I got around 10 minutes after the power on.

On Tue, Jun 19, 2012 at 4:53 PM, Nick Foster <nick at ettus.com> wrote:

> Dario,
>
> Also, please try configuring the USRP for "external" reference as you did
> for the cesium test previously. Then connect the GPSDO to the external
> reference input and see if kal gives reasonable error.
>
> It does seem like you may have a faulty reference input.
>
> --n
>
> On Tue, Jun 19, 2012 at 4:45 AM, John Malsbury <john.malsbury at ettus.com>wrote:
>
>> Just for grins, can you remove the eeprom config that enables the
>> internal gpsdo?  What results do you see from kal when the internal tcxo on
>> the motherboard is used?
>>
>> BTW, are you getting reasonable gga strings that correlate to your known
>> position?
>>
>>
>> John
>>
>> On Tuesday, June 19, 2012, Dario Lombardo <dario.lombardo.ml at gmail.com>
>> wrote:
>> > Hi Josh
>> >
>> > On Tue, Jun 19, 2012 at 1:14 PM, John Malsbury <john.malsbury at ettus.com>
>> wrote:
>> >>
>> >> Dario,
>> >>
>> >> Forgive me if I am not able to see your previous posts as I am
>> answering from my phone.  Are you saying there is
>> >> 11 khz of error in the 10 mhz ref, or some frequency set to a
>> daughterboard LO?
>> >
>> > I'm saying that error is the output of kalibrate.
>> >
>> >>
>> >> You mention using an external reference.  I don't think you would
>> achieve lock if this were the issue, but have you ensured the jumper is in
>> the proper configuration?
>> >
>> > When using the front panel connectors, I moved the jumper J510 to
>> select them. In this case I got 0 Hz of error at my first try. To be sure,
>> I disconnected the gpsdo from the mainboard.
>> >
>> >>
>> >> Are you selecting default or external as the ref source in your
>> software?
>> >
>> > When using the gpsdo, I moved the jumper J510, then configured the
>> eeprom to "internal". In this case I suppose that the N210 automatically
>> selects the gpsdo. In fact every time I run something I see
>> > -- Opening a USRP2/N-Series device...
>> > -- Current recv frame size: 1472 bytes
>> > -- Current send frame size: 1472 bytes
>> > -- Found a Jackson Labs GPS
>> > -- Setting references to the internal GPSDO
>> > -- Initializing time to the internal GPSDO
>> > no matter if any "external ref" is used or not. In kal, I got that
>> error with and without the "-x" switch.
>> >>
>> >> John
>> >>
>> >> On Tuesday, June 19, 2012, Dario Lombardo <dario.lombardo.ml at gmail.com>
>> wrote:
>> >> > Hi all
>> >> > After many tries with my gpsdo, I still can't get a good clock.
>> >> > I've written a sw that continuously polls the gps_locked and the
>> ref_locked sensors. Both of them are always locked, that means that my
>> antenna is getting a quite "clear" sky view.
>> >> > I've connected the front panel connectors of my N210 to a cesium
>> clock/pps generator, and I get 2 to 0 Hz of error with kal. That should
>> mean that my usrp works fine and the kal commands are good.hu
>> >> > I've left the usrp turned on, with the gps antenna connected, for
>> over 20 hours, but kal still gives me around 11 kHz of error.
>> >> > I think that one of these 2 things is happening:
>> >> > 1) my gpsdo card is broken. What can I do to ensure that this is not
>> the case? And if this is the case, what can I do?
>> >> > 2) my antenna can't give a signal that is clear enough, so the gpsdo
>> isn't unable to give me the clock.
>> >> > What do you think about the above cases?
>> >> > Any help appreciated.
>> >> > Dario.
>>
>> Just for grins, can you remove the eeprom config that enables the
>> internal gpsdo?  What results do you see from kal when the internal tcxo on
>> the motherboard is used?
>>
>> Are you getting reasonable gga strings that correlate to your known
>> position?
>>
>>
>> John
>>
>> On Tuesday, June 19, 2012, Dario Lombardo <dario.lombardo.ml at gmail.com>
>> wrote:
>> > Hi Josh
>> >
>> > On Tue, Jun 19, 2012 at 1:14 PM, John Malsbury <john.malsbury at ettus.com>
>> wrote:
>> >>
>> >> Dario,
>> >>
>> >> Forgive me if I am not able to see your previous posts as I am
>> answering from my phone.  Are you saying there is
>> >> 11 khz of error in the 10 mhz ref, or some frequency set to a
>> daughterboard LO?
>> >
>> > I'm saying that error is the output of kalibrate.
>> >
>> >>
>> >> You mention using an external reference.  I don't think you would
>> achieve lock if this were the issue, but have you ensured the jumper is in
>> the proper configuration?
>> >
>> > When using the front panel connectors, I moved the jumper J510 to
>> select them. In this case I got 0 Hz of error at my first try. To be sure,
>> I disconnected the gpsdo from the mainboard.
>> >
>> >>
>> >> Are you selecting default or external as the ref source in your
>> software?
>> >
>> > When using the gpsdo, I moved the jumper J510, then configured the
>> eeprom to "internal". In this case I suppose that the N210 automatically
>> selects the gpsdo. In fact every time I run something I see
>> > -- Opening a USRP2/N-Series device...
>> > -- Current recv frame size: 1472 bytes
>> > -- Current send frame size: 1472 bytes
>> > -- Found a Jackson Labs GPS
>> > -- Setting references to the internal GPSDO
>> > -- Initializing time to the internal GPSDO
>> > no matter if any "external ref" is used or not. In kal, I got that
>> error with and without the "-x" switch.
>> >>
>> >> John
>> >>
>> >> On Tuesday, June 19, 2012, Dario Lombardo <dario.lombardo.ml at gmail.com>
>> wrote:
>> >> > Hi all
>> >> > After many tries with my gpsdo, I still can't get a good clock.
>> >> > I've written a sw that continuously polls the gps_locked and the
>> ref_locked sensors. Both of them are always locked, that means that my
>> antenna is getting a quite "clear" sky view.
>> >> > I've connected the front panel connectors of my N210 to a cesium
>> clock/pps generator, and I get 2 to 0 Hz of error with kal. That should
>> mean that my usrp works fine and the kal commands are good.hu
>> >> > I've left the usrp turned on, with the gps antenna connected, for
>> over 20 hours, but kal still gives me around 11 kHz of error.
>> >> > I think that one of these 2 things is happening:
>> >> > 1) my gpsdo card is broken. What can I do to ensure that this is not
>> the case? And if this is the case, what can I do?
>> >> > 2) my antenna can't give a signal that is clear enough, so the gpsdo
>> isn't unable to give me the clock.
>> >> > What do you think about the above cases?
>> >> > Any help appreciated.
>> >> > Dario.
>> >
>>
>> _______________________________________________
>> USRP-users mailing list
>> USRP-users at lists.ettus.com
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>
>>
>
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