Hi
> On Mar 17, 2022, at 8:57 PM, Krishna Makhija wrote:
>
> Good day everyone,
>
> I ran a few additional tests to figure this issue out. The first test
> involved using one GPS antenna for both units. I found that while phase
> coherence was better in general, there was still a fair bit of
Good day everyone,
I ran a few additional tests to figure this issue out. The first test
involved using one GPS antenna for both units. I found that while phase
coherence was better in general, there was still a fair bit of disagreement
between them. I then tried to use the 1PPS from one GPSDO as
Hi
> On Mar 9, 2022, at 5:00 PM, Hal Murray wrote:
>
>
> kb...@n1k.org said:
>> If your drone is moving at 15 KPH, that???s a bit over 4 m/s. Roughly
>> speaking, you would need updates at > 10 per second to keep this from
>> dominating the result. This would be true of both survey and
kb...@n1k.org said:
> If your drone is moving at 15 KPH, that???s a bit over 4 m/s. Roughly
> speaking, you would need updates at > 10 per second to keep this from
> dominating the result. This would be true of both survey and direct time of
> flight measurements.
Do I really need that
Hi
The timestamping in a real implementation should be done in the FPGA or on
a SoC integrated in the FPGA. Since you have a SDR you could implement a
timestamping core.
This timestamping core takes the samples from the ADC and calculates the
time of arrival relative to the sampling clock.
If you
Hi
If you have a clock in motion and want to send it a time signal,
the speed of light will always get into the process. A nanosecond
is roughly 30 CM. To hit a half nanosecond, you need to know the
location to within 15 CM. If you are doing this by survey techniques
( = GPS), that would be
Hello Mattia,
Thanks for the paper. Please correct me if I understood wrong, but it seems
like you are calculating the time of flight between timestamped signals to
synchronize two spatially separated clocks. Since there is some
non-deterministic computational overhead, you need to take several
Where are the GPS antennas wrt. you 'moving around'?
Could it be that while you were watching the paint drying, you didn't move
much. But when you moved away, the RF pattern as a result of local
reflections of the signal from the satellites (from you) were enough to
upset the receiver to give
HI
> On Mar 8, 2022, at 2:31 AM, ed breya wrote:
>
> Just an interesting observation. Last night, shortly after I wrote about my
> dual GPSDO system, I decided to take a look at it, with the usual scope setup
> looking at both 10 MHz outputs. It looked like one of those reasonably good
>
Just an interesting observation. Last night, shortly after I wrote about
my dual GPSDO system, I decided to take a look at it, with the usual
scope setup looking at both 10 MHz outputs. It looked like one of those
reasonably good times, where the phase between them seemed very stable
during
> I've had the same question but I can't see how it could possibly "know"
> its own frequency error/uncertainty. What would it reference to?
That's why it's a rough internal *estimate*, not an actual measurement
against an external reference. Again, it goes back to how a GPSDO works.
There is
Hi,
You can definitely get sub-ns precision using a 4-8 MHz bandwidth wireless
protocol. You are not limited by the sampling period. In my previous work I
used 802.15.4-CSS (chirp based modulation), implemented by me in a SDR. The
sampling rate was 32 ns but with crosscorrelation and sample
Hi
As soon as you put one device in motion relative to the other
and space them apart, the expected level of alignment between
the PPS outputs will drop. You are adding a number of variables
into the mix.
As noted in other posts, something like a F9T or a Mosiac T is
a much better way to do
Thanks Mattia. What did you use for your Layer 1? I need to place one of
the SDRs on a drone and one on the ground so a fiber or LAN cable is out. I
could use WLAN but can you get sub-nanosecond performance over wi-fi? My
initial guess would be no but I am not certain.
Michael: I've had the same
Hello Krishna,
what is your end application? How far away are those boards?
If each SDR can communicate to each other, you can run PTP over an ad-hoc
Layer 1.
I was able to get timestamps out of a 2.4 GHz chirp-based protocol with
less than 0.5ns RMS noise and two-way ranging error down to 10-20
Hi Krishna,
> Hello Tom,
> Yes, the GPSDOs are working well. However, when I use each as a reference
> to a separate radio, I find there is a slow phase change over time
between
> said radios. I imagine this is expected since there will always be some
> error between two discrete oscillators.
Dear Krishna
You should probably check with the manufacturer exactly how one should
interpret eg SYNC:FEE?
The manual says:
"This query returns the Frequency Error Estimate."
but is this a offset due to eg a DAC resolution limitation, or is it
the uncertainty in the frequency?
I am guessing it
I actually have this kind of setup, with two "identical" GPSDO boards I
salvaged from some telecom gear long ago. I've yet to be able to
identify them by make or model. All I know is they use Oncore UT or GT
RX units, and seem to work, according to the LED indicators and the 10
MHz outputs.
On 3/6/22 1:36 PM, Krishna Makhija wrote:
Hello Tom,
Yes, the GPSDOs are working well. However, when I use each as a reference
to a separate radio, I find there is a slow phase change over time between
said radios. I imagine this is expected since there will always be some
error between two
Hello Tom,
Yes, the GPSDOs are working well. However, when I use each as a reference
to a separate radio, I find there is a slow phase change over time between
said radios. I imagine this is expected since there will always be some
error between two discrete oscillators. However, I am hoping to
Hi
They *are* phase coherant to within 360 * 100/ 10 = 36 degrees. You
can get them to *maybe* ten degrees with this and that done here or there.
If you want them within a degree, no you can’t do that directly with GPS.
If your definition of phase coherent is zero degrees, a pair of SDR’s off
On 3/6/22 10:48 AM, Bob kb8tq wrote:
Hi
How close are you trying to get?
How far apart are the GPSDO’s?
A “run of the mill” number would be out around 100 ns. A “pretty good”
number is in the 20 ns range. A “crazy good” number would be 2 ns. To
do better than this, you likely would need to go
Hi
How close are you trying to get?
How far apart are the GPSDO’s?
A “run of the mill” number would be out around 100 ns. A “pretty good”
number is in the 20 ns range. A “crazy good” number would be 2 ns. To
do better than this, you likely would need to go to a more exotic configuration
on
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