Thanks Marcus,
So it appears that the synching of the SBX LOs doesn’t
work; or perhaps I should say, it doesn’t work during my measurement period?
The integer-N tuning doesn’t work either.
I can say that, with some level of precision, the phase
is fairly constant with center-frequency but if, for example, I had a 5 MHz
spectrum how could I ‘correct for that’? I be;ieve that there is the whole
Hilbert transform issue when you wish to translate the phase/frequency of a
band of signals to a different one –is that what I should use?
From my point of view, there is quite a
misinterpretation of what ‘synchronistation’ means; in particular for SBXs and
their LOs which, as advertised, are supposed to be capable of such operation
with a few simple Python commands!.
Realising that you would/should not express some
shortcoming in the SBX,N200,MIMO in an Ettus product , if there is, I would
dearly like to know from someone from Ettus!!!! Purely from an outside point of
view, I thought that the “ we’ll transfer the Time Of Day contents to the Mate
over MIMO cable ” doesn’t actually mean that they are in ‘real time’ synch,
from my old DMS-100 days bit was willing to go along with the theory.
Seriously, I have no issue with that but just want to know how to get 2 N200r4
streams with OB GPSDO & MIMO cable ‘synchronised’
I would love (but be embarrassed) to be told, that as a
dummy, I made this mistake but in over a month of work I have not been able to
establish that.
Kind Regards,
John
From: mle...@ripnet.com
Sent: Wednesday, October 25, 2017 7:45 AM
To: John Shields
Cc: usrp-users
Subject: Re: [USRP-users] 2 N200 MIMO system phase offset varies with
frequency, have used timed_command with tune and also integer-N Tuning per
Marcus M post of Feb 17, 2016
I would expect component tolerance issues on the two sides to scale with
frequency. That may be what you're seeing?
On 2017-10-24 14:28, John Shields via USRP-users wrote:
Hi,
Still struggling with the configuration – 2x N200 r4, master O/B GPSDO,
slave MIMO cable. Have put in python code to use timed commands and that
produced a constant phase offset even over rerun of FG or power cycling on N200
which was great news.
However, the relative offset changes with frequency. The splitter is a
Mini-circuits ZRFSC-123S+ which is spec-ed to has a typical of phase unbalance
of 1/2 a degree over the frequency ranges used. The results are independent of
source NWT 4000-1 or an SBX using uhd_siggen. When I have checked the
ref_locked flags etc. they are good. the gpsdo is 'locked' as is MIMO.
In addition to using the timed_commands to synch the SBX LOs, I also
implement the integer-N-tuning and no improvement.
The results are roughly Freq (MHz) Phase offset (deg)
450 -7
1450 -30
1950 -65
2450 -100
When I switch the cables between the 2 N200, the phase offset doesn't
change sign so I presume it is not cabling? What on earth, else, could it be?
Kind Regards,
John
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