On 03/19/2019 09:12 PM, Damon wrote:
Hi Marcus,
The phase responses of two channels of different dboards (ubx-160)
in a X310 are very consistent. When the frequency of transmitting
signal changes from 460.01MHz to 460.03Mhz, the phase difference
between two RX channels of different dboards in X310 remains
unchanged. But for the phase difference between two RX channels of
different dboards of N310, there are dozens or hundreds degree of
changes.
Can you try to reproduce the test and help me to figure out how to
solve it?
I'm not sure if it's a hardware bug, a driver bug or USRP setup problem.
I cannot imagine a hardware or driver bug that could produce this
behavior. It would mean that the receiver was somehow changing LO
frequency when the TX frequency changed.
Does this happen with *other* frequency changes, or just
460.01<--->460.03. I wonder if you have an interfering signal that is being
"uncovered" by TX frequency change, and you're simply measuring that
interfering signal?
The only other thing that occurs to me is filtering that is extremely
non-linear phase. But that would create such a mess that most applications
would likely not work--clearly they do.
I can try to reproduce in my lab tomorrow, but, like the last tests I
did, I very much expect to not be able to reproduce.
Best regards,
Damon
On 2019/3/19 上午6:10, Marcus D. Leech wrote:
On 03/18/2019 01:26 PM, Damon wrote:
Hi Marcus,
Sorry, I can't reproduce the first observation in this discussion
thread. A new problem about phase response has arisen.
I am testing the phase coherence performance of four receiving
channels of N310. A B200 is transmitting single tone continuous wave
to a one to four splitter. The 4 outputs of the splitter are
connected to 4 RX channels of N310. Attached please find the GRC
file of this test.
The RX frequency of 4 channels of N310 is set to 460MHz, and keep
running in the test.
The TX frequency of B200 is set to 460.02MHz first, and then to
460.03MHz. I thought the phase difference between different dboards
would change very little when the signal frequency difference is
very small, similar to the performance of X310. However, the fact is
that the phase difference between the two dboards of N310 varies
considerably with the signal frequency transmission. For example, in
the attached picture, when the signal frequency is 460.01MHz, the
phase difference between channel 2 and channel 0 is -118 degrees,
the phase difference between channel 1 and channel 0 is 0 degrees;
when the transmission frequency is adjusted to 460.03MHz, the phase
difference between channel 2 and channel 0 is 117 degrees, and the
phase difference between channel 1 and channel 0 is 0 degrees. It is
very difficult to understand that the phase difference of two
receiving channels of two different dboards has changed by 235
degrees with the signal frequency change of 20 KHz. The phase
difference of two receiving channels of the same dboard is basically
unchanged.
Best regards,
Damon
Since the LO on the daughterboards has no idea that you've changed
input frequency, this is clearly a measurement thing, and it's up to you
to understand what you're measuring, and why.
On 2019/3/16 上午7:47, Marcus D. Leech wrote:
On 03/14/2019 04:37 PM, Damon wrote:
Hi Marcus,
The UHD Version is v3.14.0.0-rc1.
Best regards,
Damon
I don't see this issue at all, using v3.14.0.0-rc3
How are you measuring phase, what does you flow-graph look like?
Have you increased the gain enough to assure that the inherent system
noise is not dominating your phase measurements?
Hi Ali,
The daughterboards have their own clock generators, but they are
not
exactly 'independent'. At least they don't have to be, as they
share the
same reference clock. Look at the block diagram:
https://kb.ettus.com/images/9/9d/USRP_N310_N300_DB_Schematic.pdf
and "Ref Clock" block. I don't have N310 and I know that reality
can be
a bit far from expectations (i.e. look at my "What makes sense
and what
doesn't in the way carrier frequency is set for TwinRX
currently?" post).
But maybe the daughterboards can be configured to use that
reference clock.
Best Regards,
Piotr Krysik
The LMK clock generator uses the reference clock from the
mainboard, so
there should not be any mutual phase-jitter/drift issues. I can
test this
on my N310 in the coming day or two.
What version of UHD is in use?
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