Thank you, Michael!
> On May 17, 2024, at 14:34, Michael West <michael.eric.w...@gmail.com> wrote:
>
> Hi Walter/Moses,
>
> I spent the last 10 years developing the UHD code for all the USRP devices,
> including the B210. I can tell you definitively that there is no
> "pps_locked" sensor and the "ref_locked" sensor is valid for any clock source
> (internal, external, or onboard GPSDO) and it indicates that the PLL on the
> device is locked. The "gps_locked" sensor indicates a lock to the GPS
> constellation when a GPSDO is installed on the device. Just about any GPSDO
> devices will typically produce 10 MHz and PPS signals before the internal PLL
> is locked and regardless whether it is locked to a GPS constellation or not
> (it must for holdover mode when satellites are not visible). The Octoclock-G
> has a 1GbE port and offers the "gps_locked" and "gps_time" sensors. NMEA
> strings are available through the "gps_gpgga", "gps_gprmc", and "gps_servo"
> sensors on the Octoclock or onboard GPSDO modules.
>
> Regards,
> Michael E. West
>
> On Fri, May 17, 2024 at 2:13 PM walter <wal...@hacktuary.ai
> <mailto:wal...@hacktuary.ai>> wrote:
>> Hi Moses et al -
>>
>> I spend a lot of time working with B210s on a shared 10MHz clock and PPS
>> source:
>>
>> Some cheap GPSDO products, e.g. from EBay, work - but it's not clear if
>> they're using BeiDou (or other system) as opposed to (US) GPS, and
>> Many that advertise 'four clock channels' actually have two square-wave
>> signals paired with two sine wave signals - effectively two, not four, clock
>> signals.
>> Given the price difference and value of my time, I broke down and got an NI
>> Octoclock-G, which works great and has eight (each) PPS / Clock ports.
>> For your use case, the $220 GPSDO EBay PPS/clocks may be fine - Mfr also
>> claims you can special order a four-square-wave version.
>> The main drawback with (my) $220 EBay GPSDO is having a single port for the
>> (TTL) PPS signal: in practice, providing the PPS signal to more than one
>> radio requires creating a DIY ('distribute it yourself') circuit for the PPS
>> - this can be sub-optimal, as discussed below.
>>
>> Regarding 'lock':
>> I'm 98% certain that any USRP `pps_locked` / `ref_locked` register is only
>> valid when using an internal GPSDO for the B210 or higher-end units that
>> have internal GPSDO - see 'caveat'.
>> In this context 'lock' refers to lock-on-satellite, which is a property of
>> the PPS/Clock unit, not the radio.
>> The clock and pps signals are square waves / pulses, and do not have a
>> method of coding lock status in the signal.
>> Any external GPS unit will have LED indicators for 'lock' status. Check
>> them early and often :-)
>> My $220 EBay GPSDO will produce PPS and 10MHz signals when **not** locked to
>> a GPS signal, hilarity ensues.
>> The Octoclock-G has a separate 10Gbps(?) ethernet port that can report NMEA
>> data, which I presume would indicate loss-of-lock. Since the B210 isn't
>> network-enabled, taking advantage of the NMEA info requires setting up
>> additional hardware / software. I haven't tried it yet.
>>
>> When using an external GPSDO/clock/pps with the B210, the [UHD: USRP Source
>> (or Sink)] block settings should be:
>>
>> Sync [[ Unknown PPS ]] ** see CAVEAT: Internal GPSDO
>> Mb0: Clock Source [[ External ]]
>> Mb0: Time Source [[ External ]]
>>
>> External reference signals are the 'source-of-truth' when attached - so
>> 'attached' or 'not attached' is the only status your're likely to get from
>> your B210.
>> I once forgot to connect one of the PPS/Clock cables while using the above
>> settings, and got errors due to lack of signal.
>> In general, when using clock / PPS source - and in particular when
>> distributing to multiple B210s - it's important to use identical
>> high-quality cables of equal length for both 10MHz and PPS to all radio
>> units.
>> Having different transmission-delays for PPS and 10MHz signals reduces
>> accuracy - this is why 'distribute it yourself' can be sub-optimal.
>>
>> ** CAVEAT Internal GPSDO: The use case for "Sync [[GPS Time on Next PPS]]"
>> applies *only* if you installed the internal B210 GPSDO board, which
>> disables the B210 from using a shared external clock of any kind.
>>
>> Hope this helps.
>>
>> .-- W
>>
>> ---------------
>>
>>> On May 17, 2024, at 07:19, Moses Browne Mwakyanjala <mbkit...@gmail.com
>>> <mailto:mbkit...@gmail.com>> wrote:
>>>
>>> Hi Marcus,
>>>
>>> The external 10MHz did the trick. I have another related question which I
>>> think we can address here without opening a new ticket. The USRP B210 has a
>>> 1PPS port. However, I was not able to poll the status of the time source,
>>> "pps_locked". When I searched for a list of all onboard sensors, the only
>>> visible sensor was "ref_locked". Am I missing something? How can I use and
>>> poll the status of 1PPS?
>>>
>>> Regards, Moses
>>>
>>>
>>> On Wed, May 15, 2024 at 6:04 PM <discuss-gnuradio-requ...@gnu.org
>>> <mailto:discuss-gnuradio-requ...@gnu.org>> wrote:
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>>>>
>>>> Today's Topics:
>>>>
>>>> 1. USRP B210 Frequency Offset (Moses Browne Mwakyanjala)
>>>> 2. Re: USRP B210 Frequency Offset (Marcus D. Leech)
>>>>
>>>>
>>>> ----------------------------------------------------------------------
>>>>
>>>> Message: 1
>>>> Date: Wed, 15 May 2024 11:52:27 +0200
>>>> From: Moses Browne Mwakyanjala <mbkit...@gmail.com
>>>> <mailto:mbkit...@gmail.com>>
>>>> To: GNURadio Discussion List <discuss-gnuradio@gnu.org
>>>> <mailto:discuss-gnuradio@gnu.org>>
>>>> Subject: USRP B210 Frequency Offset
>>>> Message-ID:
>>>>
>>>> <cabysgdmphq54warsy--5-7renj3pfrahtowuce_rss8ypq-...@mail.gmail.com
>>>> <mailto:cabysgdmphq54warsy--5-7renj3pfrahtowuce_rss8ypq-...@mail.gmail.com>>
>>>> Content-Type: text/plain; charset="utf-8"
>>>>
>>>> I've encountered a consistent frequency offset of around 2ppm with my new
>>>> B210. Operating at a sample rate of 4 MSPS with the "internal" clock, all
>>>> calibrations were performed using a sine wave from an Agilent signal
>>>> generator.
>>>>
>>>> Though seemingly minor, the 800Hz offset at UHF poses challenges in
>>>> receiving low-rate data from orbiting satellites. Is there an automated
>>>> method to approximate and mitigate this offset? Currently, I manually
>>>> adjust the frequency by subtracting the offset in ppm. However, I'm curious
>>>> if there are more sophisticated solutions available, excluding reliance on
>>>> GPS or a 10MHz reference.
>>>>
>>>> Best regards,
>>>> Moses
>>>>
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