Re: Discuss-gnuradio Digest, Vol 259, Issue 8

Hi Moses,

The PPS input is just a trigger that is used to set the time on the device.  There is nothing for it to lock to and currently nothing that detects the presence of the signal.  Setting the clock and time source on the USRP Sink/Source blocks to external and the Sync to "unknown PPS" will sync the device time to the PPS signal.  More directly, you can use the set_time_next_pps() and set_time_unknown_pps() methods to set the time on the device to a specific time.

Regards,

Michael E. West

On Fri, May 17, 2024 at 7:21 AM Moses Browne Mwakyanjala <mbkitine@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-request@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)


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Message: 1
Date: Wed, 15 May 2024 11:52:27 +0200
From: Moses Browne Mwakyanjala <mbkitine@gmail.com>
To: GNURadio Discussion List <discuss-gnuradio@gnu.org>
Subject: USRP B210 Frequency Offset
Message-ID:
        <CABYsGdmPhq54WArSY--5-7renj3PFrAhTOWucE_RsS8YpQ-yVQ@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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Message: 2
Date: Wed, 15 May 2024 09:10:13 -0400
From: "Marcus D. Leech" <patchvonbraun@gmail.com>
To: discuss-gnuradio@gnu.org
Subject: Re: USRP B210 Frequency Offset
Message-ID: <ec4c50e0-0e19-494a-b25b-f273464fe402@gmail.com>
Content-Type: text/plain; charset="utf-8"; Format="flowed"

On 15/05/2024 05:52, Moses Browne Mwakyanjala wrote:
> 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
The on-board clock on a B210 is good to about 2.5PPM.  So, it's working
as you would expect.

There's nothing built in to the UHD API for this, because normally, if
you care about clock accuracy beyond what the internal clock
   can supply, you use an external, better, clock.   GPSDOs are not very
expensive these days, and you can pick up used
   10MHz OCXO units fairly cheaply as well...


>
> image.png
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