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View all threadsN310 correct choice for coherent 4 channel RX w/ 1 TX ?
Hi all,
I'm currently using a USRP N310 for an application that requires coherent 4 channel RX w/ the ability to TX on 1 channel as well. In the past, I've used USRP X310s to do 4 channel coherent RX and found the calibration process for that to be relatively straight forward using the TwinRX cards. It was simply phase aligned input signals into each RX port and computing the constant phase offset between channels and just adjusting for that factor in my processing digitally.
My understanding is that this is more complicated w/ the N310. The procedure as I understand is that during initialization the N310 external LO needs to be set at 5 GHz. After initialization, the external LO can be set to 2 times the desired center freq, but that there is still a 180 deg ambiguity between channels which would need to be figured out via calibration w/ a phase aligned input signal. Is this correct? Is there some way to shorten or optimize this procedure?
Second question would be if the process is simpler on different USRP models akin to how the X310 w/ TwinRX cards work where you just need to compute some calibration values once at powerup and afterwards those values hold pretty true for a long time as long as your gain/center freq don't change. Having the requirement of being able to TX on at least 1 channel prevents me from using an X310 w/ TwinRX cards.
Thanks,
-David
On 26/07/2023 16:47, David J Li wrote:
Hi all,
I’m currently using a USRP N310 for an application that requires
coherent 4 channel RX w/ the ability to TX on 1 channel as well. In
the past, I’ve used USRP X310s to do 4 channel coherent RX and found
the calibration process for that to be relatively straight forward
using the TwinRX cards. It was simply phase aligned input signals into
each RX port and computing the constant phase offset between channels
and just adjusting for that factor in my processing digitally.
My understanding is that this is more complicated w/ the N310. The
procedure as I understand is that during initialization the N310
external LO needs to be set at 5 GHz. After initialization, the
external LO can be set to 2 times the desired center freq, but that
there is still a 180 deg ambiguity between channels which would need
to be figured out via calibration w/ a phase aligned input signal. Is
this correct? Is there some way to shorten or optimize this procedure?
The phase ambiguity arises from the 2XLO mixing in the RFIC chips, and
there's no way around it.
You might look at the N320/N321 family for multi-channel coherent TX/RX
applications.
Second question would be if the process is simpler on different USRP
models akin to how the X310 w/ TwinRX cards work where you just need
to compute some calibration values once at powerup and afterwards
those values hold pretty true for a long time as long as your
gain/center freq don’t change. Having the requirement of being able to
TX on at least 1 channel prevents me from using an X310 w/ TwinRX cards.
Thanks,
-David
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Thanks for the suggestion, Marcus. The N320 and N321 are only both 2 TX/RX devices as far as I can tell, so to satisfy 4 RX, 1 TX it looks like I would need 2 devices. Do you happen to know if there is any official documentation on using the external LO for the N310 hidden somewhere on the Ettus wiki? The 5 GHz external LO initial input requirement doesn’t seem to be documented anywhere as far as I can tell.
From: Marcus D. Leech patchvonbraun@gmail.com
Sent: Wednesday, July 26, 2023 4:51 PM
To: usrp-users@lists.ettus.com
Subject: [EXT] [USRP-users] Re: N310 correct choice for coherent 4 channel RX w/ 1 TX ?
ZjQcmQRYFpfptBannerEnd
On 26/07/2023 16:47, David J Li wrote:
Hi all,
I’m currently using a USRP N310 for an application that requires coherent 4 channel RX w/ the ability to TX on 1 channel as well. In the past, I’ve used USRP X310s to do 4 channel coherent RX and found the calibration process for that to be relatively straight forward using the TwinRX cards. It was simply phase aligned input signals into each RX port and computing the constant phase offset between channels and just adjusting for that factor in my processing digitally.
My understanding is that this is more complicated w/ the N310. The procedure as I understand is that during initialization the N310 external LO needs to be set at 5 GHz. After initialization, the external LO can be set to 2 times the desired center freq, but that there is still a 180 deg ambiguity between channels which would need to be figured out via calibration w/ a phase aligned input signal. Is this correct? Is there some way to shorten or optimize this procedure?
The phase ambiguity arises from the 2XLO mixing in the RFIC chips, and there's no way around it.
You might look at the N320/N321 family for multi-channel coherent TX/RX applications.
Second question would be if the process is simpler on different USRP models akin to how the X310 w/ TwinRX cards work where you just need to compute some calibration values once at powerup and afterwards those values hold pretty true for a long time as long as your gain/center freq don’t change. Having the requirement of being able to TX on at least 1 channel prevents me from using an X310 w/ TwinRX cards.
Thanks,
-David
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To unsubscribe send an email to usrp-users-leave@lists.ettus.commailto:usrp-users-leave@lists.ettus.com
On 26/07/2023 17:17, David J Li wrote:
Thanks for the suggestion, Marcus. The N320 and N321 are only both 2
TX/RX devices as far as I can tell, so to satisfy 4 RX, 1 TX it looks
like I would need 2 devices. Do you happen to know if there is any
official documentation on using the external LO for the N310 hidden
somewhere on the Ettus wiki? The 5 GHz external LO initial input
requirement doesn’t seem to be documented anywhere as far as I can tell.
It is the case that there are some app-notes needed for the N310,
including the "5GHz Lore" -- this requirement comes, from
what I understand, from the AD9371 data-sheet.
There are folks on this list who have used the external LO on N310
successfully, including (I believe, please correct me if I'm
wrong) Rob Kossler.
*From:*Marcus D. Leech patchvonbraun@gmail.com
Sent: Wednesday, July 26, 2023 4:51 PM
To: usrp-users@lists.ettus.com
Subject: [EXT] [USRP-users] Re: N310 correct choice for coherent 4
channel RX w/ 1 TX ?
ZjQcmQRYFpfptBannerEnd
On 26/07/2023 16:47, David J Li wrote:
Hi all,
I’m currently using a USRP N310 for an application that requires
coherent 4 channel RX w/ the ability to TX on 1 channel as well.
In the past, I’ve used USRP X310s to do 4 channel coherent RX and
found the calibration process for that to be relatively straight
forward using the TwinRX cards. It was simply phase aligned input
signals into each RX port and computing the constant phase offset
between channels and just adjusting for that factor in my
processing digitally.
My understanding is that this is more complicated w/ the N310. The
procedure as I understand is that during initialization the N310
external LO needs to be set at 5 GHz. After initialization, the
external LO can be set to 2 times the desired center freq, but
that there is still a 180 deg ambiguity between channels which
would need to be figured out via calibration w/ a phase aligned
input signal. Is this correct? Is there some way to shorten or
optimize this procedure?
The phase ambiguity arises from the 2XLO mixing in the RFIC chips, and
there's no way around it.
You might look at the N320/N321 family for multi-channel coherent
TX/RX applications.
Second question would be if the process is simpler on different
USRP models akin to how the X310 w/ TwinRX cards work where you
just need to compute some calibration values once at powerup and
afterwards those values hold pretty true for a long time as long
as your gain/center freq don’t change. Having the requirement of
being able to TX on at least 1 channel prevents me from using an
X310 w/ TwinRX cards.
Thanks,
-David
_______________________________________________
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To unsubscribe send an email tousrp-users-leave@lists.ettus.com
Hi David,
You seem to already know the essentials based on the previous comments.
I have used each of the following USRPs in various 4-channel
coherent experiments. I'll mention a couple of comments about each.
- The X310/UBX can be phase calibrated, but it can't operate with a
shared LO - The X310/TwinRx can also be phase calibrated and it can operate with a
shared LO, but there is no transmit channel - The N310 can be phase calibrated and can operate with an external
shared LO but with the 180 deg ambiguity you mentioned. However each
"pair" of Rx or Tx share the same circuitry so they inherently share the
same ambiguity. Thus, if channel 0 is +180 on this calibration, then
channel 1 will also be +180. The N310 can used shared LO as you mentioned
with the 5GHz startup calibration but it does not operate above 4 GHz (ext
LO at 8 GHz) - The N321 can share LO among all Tx and Rx channels (I have implemented
16x16). In this configuration, it is easy to get the same phase calibration
every time since the LO is shared. This is a great choice if you can
tolerate the additional expense, size, and weight of two devices.
Depending on "just how coherent" you need to be affects whether you
want/need "shared LO". If the LO is not shared, then each LO disciplines
to a common reference signal. This can provide a consistent average phase
offset among channels (as in the X310/UBX), but the instantaneous phase of
a given channel can deviate based on its individual phase locked loop
(PLL). All of the PLLs will keep the relative phase/frequency within a
tolerance, but it is not the same as a shared LO for which slight
deviations will be identical on every channel.
Rob
On Wed, Jul 26, 2023 at 5:30 PM Marcus D. Leech patchvonbraun@gmail.com
wrote:
On 26/07/2023 17:17, David J Li wrote:
Thanks for the suggestion, Marcus. The N320 and N321 are only both 2 TX/RX
devices as far as I can tell, so to satisfy 4 RX, 1 TX it looks like I
would need 2 devices. Do you happen to know if there is any official
documentation on using the external LO for the N310 hidden somewhere on the
Ettus wiki? The 5 GHz external LO initial input requirement doesn’t seem to
be documented anywhere as far as I can tell.
It is the case that there are some app-notes needed for the N310,
including the "5GHz Lore" -- this requirement comes, from
what I understand, from the AD9371 data-sheet.
There are folks on this list who have used the external LO on N310
successfully, including (I believe, please correct me if I'm
wrong) Rob Kossler.
From: Marcus D. Leech patchvonbraun@gmail.com
patchvonbraun@gmail.com
Sent: Wednesday, July 26, 2023 4:51 PM
To: usrp-users@lists.ettus.com
Subject: [EXT] [USRP-users] Re: N310 correct choice for coherent 4
channel RX w/ 1 TX ?
ZjQcmQRYFpfptBannerEnd
On 26/07/2023 16:47, David J Li wrote:
Hi all,
I’m currently using a USRP N310 for an application that requires coherent
4 channel RX w/ the ability to TX on 1 channel as well. In the past, I’ve
used USRP X310s to do 4 channel coherent RX and found the calibration
process for that to be relatively straight forward using the TwinRX cards.
It was simply phase aligned input signals into each RX port and computing
the constant phase offset between channels and just adjusting for that
factor in my processing digitally.
My understanding is that this is more complicated w/ the N310. The
procedure as I understand is that during initialization the N310 external
LO needs to be set at 5 GHz. After initialization, the external LO can be
set to 2 times the desired center freq, but that there is still a 180 deg
ambiguity between channels which would need to be figured out via
calibration w/ a phase aligned input signal. Is this correct? Is there some
way to shorten or optimize this procedure?
The phase ambiguity arises from the 2XLO mixing in the RFIC chips, and
there's no way around it.
You might look at the N320/N321 family for multi-channel coherent TX/RX
applications.
Second question would be if the process is simpler on different USRP
models akin to how the X310 w/ TwinRX cards work where you just need to
compute some calibration values once at powerup and afterwards those values
hold pretty true for a long time as long as your gain/center freq don’t
change. Having the requirement of being able to TX on at least 1 channel
prevents me from using an X310 w/ TwinRX cards.
Thanks,
-David
USRP-users mailing list -- usrp-users@lists.ettus.com
To unsubscribe send an email to usrp-users-leave@lists.ettus.com
USRP-users mailing list -- usrp-users@lists.ettus.com
To unsubscribe send an email to usrp-users-leave@lists.ettus.com
On 27/07/2023 18:13, Rob Kossler wrote:
Depending on "just how coherent" you need to be affects whether you
want/need "shared LO". If the LO is not shared, then each LO
disciplines to a common reference signal. This can provide a
consistent average phase offset among channels (as in the X310/UBX),
but the instantaneous phase of a given channel can deviate based on
its individual phase locked loop (PLL). All of the PLLs will keep the
relative phase/frequency within a tolerance, but it is not the same as
a shared LO for which slight deviations will be identical on every
channel.
Rob
I have described high-precision-coherence requirements as "brutal
coherence" ('brutal' because designing hardware that
provides such is, well, a 'brual' task).
My own application for coherence--astronomical interferometry benefits
most from a completely-shared-LO scheme, along with
the necessary DSP bits that both guarantee zero mutual phase noise,
and ideally, no channel-to-channel phase offset.
Ironically enough, in the "olden days" of interferometry, even if your
LO (that was shared among all your receive chains)
was kinda crappy from a phase-noise perspective, it didn't matter,
because ALL the channels were "shaking and shimmering"
together at the same instant in time--so their mutual phase-noise was
quite low.
Once you bring one-synth-per-channel into the mix, then you have a
couple of problems to deal with, even with a shared
reference clock:
A higher mutual phase noise
B often unpredictable phase offset
Whether (A) is a serious problem depends very much on your
application--in astronomical interferometry, your
correlation SNR degrades with mutual phase noise, but one tends to
integrate for long periods, so it's not
a total disaster.
For (B), this can usually be calibrated out at the start of a "run"
(whatever that means in your application). Radio observatories
do this even when they have a "brutally coherent" receiving set-up,
because analog bits and pieces up near the antenna, and
signal distribution systems often impart differential phase offsets
due to temperature effects. So, even there, with
a "brutally coherent" setup, there's a phase-offset calibration done
at the start...
On Wed, Jul 26, 2023 at 5:30 PM Marcus D. Leech
patchvonbraun@gmail.com wrote:
On 26/07/2023 17:17, David J Li wrote:
Thanks for the suggestion, Marcus. The N320 and N321 are only
both 2 TX/RX devices as far as I can tell, so to satisfy 4 RX, 1
TX it looks like I would need 2 devices. Do you happen to know if
there is any official documentation on using the external LO for
the N310 hidden somewhere on the Ettus wiki? The 5 GHz external
LO initial input requirement doesn’t seem to be documented
anywhere as far as I can tell.
It is the case that there are some app-notes needed for the N310,
including the "5GHz Lore" -- this requirement comes, from
what I understand, from the AD9371 data-sheet.
There are folks on this list who have used the external LO on N310
successfully, including (I believe, please correct me if I'm
wrong) Rob Kossler.
*From:*Marcus D. Leech <patchvonbraun@gmail.com>
<mailto:patchvonbraun@gmail.com>
*Sent:* Wednesday, July 26, 2023 4:51 PM
*To:* usrp-users@lists.ettus.com
*Subject:* [EXT] [USRP-users] Re: N310 correct choice for
coherent 4 channel RX w/ 1 TX ?
ZjQcmQRYFpfptBannerEnd
On 26/07/2023 16:47, David J Li wrote:
Hi all,
I’m currently using a USRP N310 for an application that
requires coherent 4 channel RX w/ the ability to TX on 1
channel as well. In the past, I’ve used USRP X310s to do 4
channel coherent RX and found the calibration process for
that to be relatively straight forward using the TwinRX
cards. It was simply phase aligned input signals into each RX
port and computing the constant phase offset between channels
and just adjusting for that factor in my processing digitally.
My understanding is that this is more complicated w/ the
N310. The procedure as I understand is that during
initialization the N310 external LO needs to be set at 5 GHz.
After initialization, the external LO can be set to 2 times
the desired center freq, but that there is still a 180 deg
ambiguity between channels which would need to be figured out
via calibration w/ a phase aligned input signal. Is this
correct? Is there some way to shorten or optimize this
procedure?
The phase ambiguity arises from the 2XLO mixing in the RFIC
chips, and there's no way around it.
You might look at the N320/N321 family for multi-channel coherent
TX/RX applications.
Second question would be if the process is simpler on
different USRP models akin to how the X310 w/ TwinRX cards
work where you just need to compute some calibration values
once at powerup and afterwards those values hold pretty true
for a long time as long as your gain/center freq don’t
change. Having the requirement of being able to TX on at
least 1 channel prevents me from using an X310 w/ TwinRX cards.
Thanks,
-David
_______________________________________________
USRP-users mailing list --usrp-users@lists.ettus.com
To unsubscribe send an email tousrp-users-leave@lists.ettus.com
_______________________________________________
USRP-users mailing list -- usrp-users@lists.ettus.com
To unsubscribe send an email to usrp-users-leave@lists.ettus.com