Thanks both,
All good now - I get a roughly constant phase delta
and when I re-run the FG, I get a different phase delta ( I don't need
to power cycle the USRPs). Now I will put in the synchronisation code
and the phase offset should be close to zero.
Kind Regards,
John
On 12/09/17 21:12, mle...@ripnet.com wrote:
Use "unknown PPS" on both of them. The MIMO cable shares both
REFCLOCK and 1PPS signals, so they will both be synchronized to the
same time.
On 2017-09-12 16:13, John Shields wrote:
Thanks Derek,
No, I hadn't been power cycling between the
runs - good point, obviously, I should have.
In terms of the 10 MHz and 1 pps references,
in the configuration I was testing, I don't believe so in that I had
the MIMO cable disconnected. My strategy was to have 2 USRPs with no
MIMO - expecting little synchonisation. Then I was going to add the
devices into the same container and connect the MIMO cable and
expected things to improve and lastly, I was going to hand-code the
SBX phase synch code.
In terms of the version of UHD, the fg shows:
<<< Welcome to GNU Radio Companion 3.7.11.1 >>>
Thanks Marcus,
I will implement your way of measuring the
running phase offset and also thanks for correcting my understanding
of O/B GPS .
In terms of getting the devices in the
container to be the best synch they can be, I presume for the device
which has the GPS, for the clock source and time source, I would put
O/B GPS for the device which has it and for the other, I would put
MIMO cable for both but in terms of the 'Sync' field, where the
options are PC Clock, Unknown PPS and Don't Sync, which option should
I select?
Thanks again for your help.
Kind Regards,
John
On 11/09/17 09:00, Derek Kozel wrote:
Hi John,
Are you power cycling the USRPs between tests or just rerunning the
GRC flowgraph? Do you have shared 10 MHz and 1 PPS references? What
version of UHD is printed in the output?
Thanks,
Derek
On Mon, Sep 11, 2017 at 1:50 AM, John Shields <sla1nte2...@gmail.com
<mailto:sla1nte2...@gmail.com>> wrote:
Thanks for the feedback but I am not sure that I understand it.
What I was hoping to do was step through the configurations with
increasing levels of synchronisation and expecting to see same.
Marcus' comment is correct and I have not, yet, put in the code
which synchronises SBXs.
I guess my basic point, from looking at previous post from
others Marcus L included, was that UHD would somehow improve the
synchronisation between two USRPs in the same container versus
those two separately.
When I executed the FG shown (separately) with the USRPs
individually and then within a UHD container the results in
terms of phase variation was the same. I had expected that,
based on my understanding, the containerised USRPs would have
behaved better.
So, either my FG does not measure what I thought it should or
there is little UHD-related benefit to having USRPs individually
or in the 'domain' as MarcusL has mentioned previously. From my
situation it doesn't hence the first question in the post:
Does my FG not measure what I claim to be wishing
to measure?
Kind Regards,
John
On 11/09/17 01:03, Marcus D. Leech wrote:
On 09/10/2017 08:58 PM, Dan CaJacob wrote:
I could be wrong, but I thought the SBX was one of the few
daughter cards that starts with s known phase offset?
Only if you ask it to do so, and only if it's sharing clock
with its buddies...
On Sun, Sep 10, 2017, 2:49 PM Fulcrum Associates
<sla1nte2...@gmail.com <mailto:sla1nte2...@gmail.com>> wrote:
Dear All,
I have a couple of USRPs connected, through
a strong
attenuator to a signal generator (NWT4001). While the
units have a MIMO
option, I don't have that cable. (Option A) When I run the
GRC as
attached, I see too good a result to the extent that the
differential
Phi seems to range over +/- 5 degrees.
What I had hoped to prove to myself that two
N200 with SBX
would have a varying offset without MIMO cable, then I
would connect the
MIMO cable and move the USRPs into a multi-unit and enable
GPSD O/B on
the unit which has the feature and MIMO for one without
(Option B) and
that the phase differential would improve noticeably and
be a variable
constant, but it didn't.
If it had, but there still was a fixed
phase offset which
varied each time it was setup (which is what I would
expect under B)
then I would hand-code the SBX stream initialisation code
to remove the
offset.
Does my FG not measure what I claim to be
wishing to
measure?
If it does measure it correctly, why do my
expectations
of options A and B leading to a different (though
improved) situation
not eventuate?
Kind Regards,
John
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Very Respectfully,
Dan CaJacob
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