usrp-users@lists.ettus.com
Discussion and technical support related to USRP, UHD, RFNoC
View all threadsB210 Frequency Stability versus Frequency Accuracy
On 18/04/2024 09:00, Martin Anderseck wrote:
You mention that self-calibration for each channel is running. Please
don’t get wrong what this calibration is doing. This ADC self-cal is
only responsible for reducing unwanted spurs in the ADCs as described
here: https://files.ettus.com/manual/page_usrp_x4xx.html#x4xx_adc_self_cal
This ADC self-cal, however, will not handle any power differences.
From what you write it’s not possible to get absolute power values, so
the relative differences are impossible to get, too. Since those
devices are SDRs and not dedicated measurement equipment it is
expected that there may be differences (not huge ones though, please
see the specs for getting an impression in figures 2 and 4:
https://www.ni.com/docs/de-DE/bundle/ettus-usrp-x410-specs/page/specs.html).
If the existing accuracy is insufficient, it is possible to use the
power API: https://files.ettus.com/manual/page_zbx.html#zbx_pwr_cal
You mention you used a loopback connection. Does that mean that you
connected cables to the front panel connectors for this? To exclude
them from the issue you might try using the internal loopback
“antenna” for both the RX and TX path (see get_rx_antennas() for a
list of antennas). This will use the internal loopback that is on the
daughterboard for each channel. When using the internal loopback
ensure you have compensated the lack of the 30 dB attenuator (e.g. by
reducing the gain on the TX side) as typically in an external
loopback you would use 30 dB attenuation
(https://kb.ettus.com/USRP_X410/X440_Getting_Started_Guide#Proper_Care_and_Handling).
For the phase difference: You don’t mention how you start the signal
generation. I guess timed commands are what you’re missing:
https://kb.ettus.com/Synchronizing_USRP_Events_Using_Timed_Commands_in_UHD
I hope that gets you a bit further.
Best regards,
Martin
*From:*zhou via USRP-users usrp-users@lists.ettus.com
Sent: Thursday, April 18, 2024 7:55 AM
To: usrp-users@lists.ettus.com
Subject: [USRP-users] Unbalanced power among antennas in X410
Hi All,
I am using X410 with UHD 4.5. There are 4 Tx and 4 Rx in this unit. I
am checking the RF signal by using loopback connection, that is, Tx is
connected to Rx in the same USRP. .
The same single tone signal is transmitted on all 4 Tx antennas, but I
find that the received power levels are significantly different among
antennas as shown in plot below. There are two ZBX daughterboards in
X410; ant0 and ant1 in the 1st board and ant2 and ant3 in the 2nd. It
seems that in the same daughterboard, power in the 1st antenna is
higher than the 2nd antenna.
The carrier frequency is 7GHz. Sampling rate 491.52MHz. In every test,
UHD does self calibration for each channel.
Apart from power difference, there is also phase difference between
antennas.
How to make tx power closer between antennas?
And, is there a way to adjust the carrier phase for individual antenna?
Inline image
Thanks for any suggestion.
Kind regards,
Hongwei
There will always be component-to-component variation in RF components,
and this tends to get worse at higher frequencies.
Such variability can sometimes be as much as a few dB, as shown above.
When you buy a piece of measurement equipment, these variations in
apparent gain are calibrated and "trimmed" at
the factory (and indeed, most pieces of test equipment require
re-calibration every few years). USRPs are not, per se,
measurement equipment, although could be used in that context once
the variability is accounted for in your particular
application.
The plot is titled "Real". If this is simply the real component of a
complex signal, then it is not possible to know the magnitude. If there is
a phase shift, then the power may have shifted into the "Imag" component.
Instead, plot the abs if you are interested in only power differences among
channels.
Hi Rob,
The transmitted signal is cos(t)+i*sin(t). The abs power will be constant. I plot the real part to show the waveform which contains both power information and phase information.
Thanks,Hongwei
On Thursday, 18 April 2024 at 16:51:22 BST, Rob Kossler via USRP-users <usrp-users@lists.ettus.com> wrote:
The plot is titled "Real". If this is simply the real component of a complex signal, then it is not possible to know the magnitude. If there is a phase shift, then the power may have shifted into the "Imag" component. Instead, plot the abs if you are interested in only power differences among channels.
USRP-users mailing list -- usrp-users@lists.ettus.com
To unsubscribe send an email to usrp-users-leave@lists.ettus.com
Hi Martin,
Thanks for mentioning the ADC self-cal. It seems that I misunderstood it. I will do a proper calibration.
Yes, the loopback connection is on the front panel.
The same cos(t)+i*sin(t) is transmitted on all four antennas simultaneously with timed command. The receive command is also timed. I can accept that there is phase offset between antennas because paths can be different slightly, for example, the RF cable length can be slightly different. As long as the offset is constant over the time, it is not a worry. I measured phase vs time. It is stable. Now, I want to know how to adjust the phase on individual antennas.
Kind regards,H.
USRP-users mailing list -- usrp-users@lists.ettus.com
To unsubscribe send an email to usrp-users-leave@lists.ettus.com
On Thursday, 18 April 2024 at 14:00:44 BST, Martin Anderseck martin.anderseck@ni.com wrote:
You mention that self-calibration for each channel is running. Please don’t get wrong what this calibration is doing. This ADC self-cal is only responsible for reducing unwanted spurs in the ADCs as described here: https://files.ettus.com/manual/page_usrp_x4xx.html#x4xx_adc_self_cal
This ADC self-cal, however, will not handle any power differences. From what you write it’s not possible to get absolute power values, so the relative differences are impossible to get, too. Since those devices are SDRs and not dedicated measurement equipment it is expected that there may be differences (not huge ones though, please see the specs for getting an impression in figures 2 and 4:https://www.ni.com/docs/de-DE/bundle/ettus-usrp-x410-specs/page/specs.html). If the existing accuracy is insufficient, it is possible to use the power API:https://files.ettus.com/manual/page_zbx.html#zbx_pwr_cal
You mention you used a loopback connection. Does that mean that you connected cables to the front panel connectors for this? To exclude them from the issue you might try using the internal loopback “antenna” for both the RX and TX path (see get_rx_antennas() for a list of antennas). This will use the internal loopback that is on the daughterboard for each channel. When using the internal loopback ensure you have compensated the lack of the 30 dB attenuator (e.g. by reducing the gain on the TX side) as typically in an external loopback you would use 30 dB attenuation (https://kb.ettus.com/USRP_X410/X440_Getting_Started_Guide#Proper_Care_and_Handling).
For the phase difference: You don’t mention how you start the signal generation. I guess timed commands are what you’re missing:https://kb.ettus.com/Synchronizing_USRP_Events_Using_Timed_Commands_in_UHD
I hope that gets you a bit further.
Best regards,
Martin
From: zhou via USRP-users usrp-users@lists.ettus.com
Sent: Thursday, April 18, 2024 7:55 AM
To: usrp-users@lists.ettus.com
Subject: [USRP-users] Unbalanced power among antennas in X410
Hi All,
I am using X410 with UHD 4.5. There are 4 Tx and 4 Rx in this unit. I am checking the RF signal by using loopback connection, that is, Tx is connected to Rx in the same USRP. .
The same single tone signal is transmitted on all 4 Tx antennas, but I find that the received power levels are significantly different among antennas as shown in plot below. There are two ZBX daughterboards in X410; ant0 and ant1 in the 1st board and ant2 and ant3 in the 2nd. It seems that in the same daughterboard, power in the 1st antenna is higher than the 2nd antenna.
The carrier frequency is 7GHz. Sampling rate 491.52MHz. In every test, UHD does self calibration for each channel.
Apart from power difference, there is also phase difference between antennas.
How to make tx power closer between antennas?
And, is there a way to adjust the carrier phase for individual antenna?
Thanks for any suggestion.
Kind regards,
Hongwei
National Instruments Dresden GmbH; Geschäftsführer (Managing Directors): John Stanton McElroy, Albert Edward Percival III, Kathleen Spurck; Sitz (Registered Office): Dresden; HRB (Commercial Register No.): 22081; Registergericht (Registration Court): Dresden
This email and any attachments are intended only for the person to whom this email is addressed and may contain confidential and/or privileged information. If you received this email in error, please do not disclose the contents to anyone, but notify the sender by return email and delete this email (and any attachments) from your system.
I’m curious as to whether the oscillators on each of the four channels are not sync’d to a common reference – either an internal or external source?
Thanks
Stuart Austin
From: zhou via USRP-users [mailto:usrp-users@lists.ettus.com]
Sent: Friday, April 19, 2024 2:12 AM
To: usrp-users@lists.ettus.com; Martin Anderseck
Subject: [USRP-users] Re: Unbalanced power among antennas in X410
Hi Martin,
Thanks for mentioning the ADC self-cal. It seems that I misunderstood it. I will do a proper calibration.
Yes, the loopback connection is on the front panel.
The same cos(t)+i*sin(t) is transmitted on all four antennas simultaneously with timed command. The receive command is also timed. I can accept that there is phase offset between antennas because paths can be different slightly, for example, the RF cable length can be slightly different. As long as the offset is constant over the time, it is not a worry. I measured phase vs time. It is stable. Now, I want to know how to adjust the phase on individual antennas.
Kind regards,
H.
USRP-users mailing list -- usrp-users@lists.ettus.com
To unsubscribe send an email to usrp-users-leave@lists.ettus.com
On Thursday, 18 April 2024 at 14:00:44 BST, Martin Anderseck martin.anderseck@ni.com wrote:
You mention that self-calibration for each channel is running. Please don’t get wrong what this calibration is doing. This ADC self-cal is only responsible for reducing unwanted spurs in the ADCs as described here: https://files.ettus.com/manual/page_usrp_x4xx.html#x4xx_adc_self_cal https://files.ettus.com/manual/page_usrp_x4xx.html#x4xx_adc_self_cal
This ADC self-cal, however, will not handle any power differences. From what you write it’s not possible to get absolute power values, so the relative differences are impossible to get, too. Since those devices are SDRs and not dedicated measurement equipment it is expected that there may be differences (not huge ones though, please see the specs for getting an impression in figures 2 and 4: https://www.ni.com/docs/de-DE/bundle/ettus-usrp-x410-specs/page/specs.html). If the existing accuracy is insufficient, it is possible to use the power API: https://files.ettus.com/manual/page_zbx.html#zbx_pwr_cal
You mention you used a loopback connection. Does that mean that you connected cables to the front panel connectors for this? To exclude them from the issue you might try using the internal loopback “antenna” for both the RX and TX path (see get_rx_antennas() for a list of antennas). This will use the internal loopback that is on the daughterboard for each channel. When using the internal loopback ensure you have compensated the lack of the 30 dB attenuator (e.g. by reducing the gain on the TX side) as typically in an external loopback you would use 30 dB attenuation (https://kb.ettus.com/USRP_X410/X440_Getting_Started_Guide#Proper_Care_and_Handling).
For the phase difference: You don’t mention how you start the signal generation. I guess timed commands are what you’re missing: https://kb.ettus.com/Synchronizing_USRP_Events_Using_Timed_Commands_in_UHD
I hope that gets you a bit further.
Best regards,
Martin
From: zhou via USRP-users usrp-users@lists.ettus.com
Sent: Thursday, April 18, 2024 7:55 AM
To: usrp-users@lists.ettus.com
Subject: [USRP-users] Unbalanced power among antennas in X410
Hi All,
I am using X410 with UHD 4.5. There are 4 Tx and 4 Rx in this unit. I am checking the RF signal by using loopback connection, that is, Tx is connected to Rx in the same USRP. .
The same single tone signal is transmitted on all 4 Tx antennas, but I find that the received power levels are significantly different among antennas as shown in plot below. There are two ZBX daughterboards in X410; ant0 and ant1 in the 1st board and ant2 and ant3 in the 2nd. It seems that in the same daughterboard, power in the 1st antenna is higher than the 2nd antenna.
The carrier frequency is 7GHz. Sampling rate 491.52MHz. In every test, UHD does self calibration for each channel.
Apart from power difference, there is also phase difference between antennas.
How to make tx power closer between antennas?
And, is there a way to adjust the carrier phase for individual antenna?
Inline image
Thanks for any suggestion.
Kind regards,
Hongwei
National Instruments Dresden GmbH; Geschäftsführer (Managing Directors): John Stanton McElroy, Albert Edward Percival III, Kathleen Spurck; Sitz (Registered Office): Dresden; HRB (Commercial Register No.): 22081; Registergericht (Registration Court): Dresden
This email and any attachments are intended only for the person to whom this email is addressed and may contain confidential and/or privileged information. If you received this email in error, please do not disclose the contents to anyone, but notify the sender by return email and delete this email (and any attachments) from your system.
On 19/04/2024 13:54, Stuart Austin wrote:
I’m curious as to whether the oscillators on each of the four channels
are not sync’d to a common reference – either an internal or external
source?
Thanks
Stuart Austin
For the most part (with some historical exceptions) the RF Synthesizers
on USRP devices use the motherboard clock
as their reference--they don't have independent clocks. In turn, the
motherboard clock can be externally referenced--either
through the front-panel, or an on-board GPSDO if so equipped.
Now, having said THAT, getting ZERO PHASE OFFSET requires some thought
and depending on which devices we're
talking about, the application has to set some configuration to make
sure the oscillator phase offset is zero.
That might involved timed commands during tuning (to force a
phase-reset feature if the synthesizer has such a feature), or
configuring actual LO-sharing, if the radio in question supports that.
Even THEN at higher frequencies, small differences in the phase-length
of things like the RF input lines, and the
LO-to-mixer lines can cause a not-precisely-zero phase offset, but at
a given temperature of the device, should be
simple to characterize by the end application. The USRPs are
generally designed to have phase-length matching
wherever possible, but even that isn't perfect. The worst case is
differential temperature effects across two or
more transmission lines carrying RF. The phase length of the lines
won't be exactly matched. This is well-known, and
it gets worse at higher frequencies (because it's the physical line
lengths changing, and that's a larger fraction of a wavelength
at higher frequencies).
*From:*zhou via USRP-users [mailto:usrp-users@lists.ettus.com]
Sent: Friday, April 19, 2024 2:12 AM
To: usrp-users@lists.ettus.com; Martin Anderseck
Subject: [USRP-users] Re: Unbalanced power among antennas in X410
Hi Martin,
Thanks for mentioning the ADC self-cal. It seems that I misunderstood
it. I will do a proper calibration.
Yes, the loopback connection is on the front panel.
The same cos(t)+i*sin(t) is transmitted on all four antennas
simultaneously with timed command. The receive command is also timed.
I can accept that there is phase offset between antennas because paths
can be different slightly, for example, the RF cable length can be
slightly different. As long as the offset is constant over the time,
it is not a worry. I measured phase vs time. It is stable. Now, I want
to know how to adjust the phase on individual antennas.
Kind regards,
H.
USRP-users mailing list -- usrp-users@lists.ettus.com
To unsubscribe send an email to usrp-users-leave@lists.ettus.com
On Thursday, 18 April 2024 at 14:00:44 BST, Martin Anderseck
martin.anderseck@ni.com wrote:
You mention that self-calibration for each channel is running. Please
don’t get wrong what this calibration is doing. This ADC self-cal is
only responsible for reducing unwanted spurs in the ADCs as described
here:
https://files.ettus.com/manual/page_usrp_x4xx.html#x4xx_adc_self_cal
https://files.ettus.com/manual/page_usrp_x4xx.html#x4xx_adc_self_cal
This ADC self-cal, however, will not handle any power differences.
From what you write it’s not possible to get absolute power values, so
the relative differences are impossible to get, too. Since those
devices are SDRs and not dedicated measurement equipment it is
expected that there may be differences (not huge ones though, please
see the specs for getting an impression in figures 2 and 4:
https://www.ni.com/docs/de-DE/bundle/ettus-usrp-x410-specs/page/specs.html).
If the existing accuracy is insufficient, it is possible to use the
power API: https://files.ettus.com/manual/page_zbx.html#zbx_pwr_cal
You mention you used a loopback connection. Does that mean that you
connected cables to the front panel connectors for this? To exclude
them from the issue you might try using the internal loopback
“antenna” for both the RX and TX path (see get_rx_antennas() for a
list of antennas). This will use the internal loopback that is on the
daughterboard for each channel. When using the internal loopback
ensure you have compensated the lack of the 30 dB attenuator (e.g. by
reducing the gain on the TX side) as typically in an external
loopback you would use 30 dB attenuation
(https://kb.ettus.com/USRP_X410/X440_Getting_Started_Guide#Proper_Care_and_Handling).
For the phase difference: You don’t mention how you start the signal
generation. I guess timed commands are what you’re missing:
https://kb.ettus.com/Synchronizing_USRP_Events_Using_Timed_Commands_in_UHD
I hope that gets you a bit further.
Best regards,
Martin
*From:*zhou via USRP-users usrp-users@lists.ettus.com
Sent: Thursday, April 18, 2024 7:55 AM
To: usrp-users@lists.ettus.com
Subject: [USRP-users] Unbalanced power among antennas in X410
Hi All,
I am using X410 with UHD 4.5. There are 4 Tx and 4 Rx in this unit. I
am checking the RF signal by using loopback connection, that is, Tx is
connected to Rx in the same USRP. .
The same single tone signal is transmitted on all 4 Tx antennas, but I
find that the received power levels are significantly different among
antennas as shown in plot below. There are two ZBX daughterboards in
X410; ant0 and ant1 in the 1st board and ant2 and ant3 in the 2nd. It
seems that in the same daughterboard, power in the 1st antenna is
higher than the 2nd antenna.
The carrier frequency is 7GHz. Sampling rate 491.52MHz. In every test,
UHD does self calibration for each channel.
Apart from power difference, there is also phase difference between
antennas.
How to make tx power closer between antennas?
And, is there a way to adjust the carrier phase for individual antenna?
Inline image
Thanks for any suggestion.
Kind regards,
Hongwei
National Instruments Dresden GmbH; Geschäftsführer (Managing
Directors): John Stanton McElroy, Albert Edward Percival III, Kathleen
Spurck; Sitz (Registered Office): Dresden; HRB (Commercial Register
No.): 22081; Registergericht (Registration Court): Dresden
This email and any attachments are intended only for the person to
whom this email is addressed and may contain confidential and/or
privileged information. If you received this email in error, please do
not disclose the contents to anyone, but notify the sender by return
email and delete this email (and any attachments) from your system.
USRP-users mailing list --usrp-users@lists.ettus.com
To unsubscribe send an email tousrp-users-leave@lists.ettus.com
