On 03/25/2021 07:01 PM, Jerrid Plymale wrote:
We currently are not using a 30dB attenuator in the coax line, I was
not aware that one was needed until you brought it up. We are looking
into getting one ordered at the moment. Could this be the cause of the
problem?
Best Regards,
Jerrid
The problem is that if you transmit directly into an RX with the TX
power turned up, you can fry the RX.
It also provides a much more realistic simulation of an over-the-air
link. ANY receiver that is designed for "Over The Air" reception will
have a pre-amp that doesn't like to receive power levels above about
-15dBm (which for over-the-air signals is very very loud).
With the noise figure of your RX (if it isn't damaged already) being
only about 4dB, it's going to be fairly sensitive to any low-level noise
that happens to get coupled out of the X3xx electronics when the
mixer and RF amplifier are "brought up" when a flow-graph is started.
Even when you're transmitting with a "0dB" setting, it can still be
producing up to about -20dBm power output--the attenuator is
31.5dB in 0.5dB steps, and the max Pout of the UBX is about +10dBm as
I recall. Now, with zeros going to the ADC, the IF port of
the mixer isn't going to be seeing much power, but it won't be seeing
exactly zero power because of the inevitable DAC noise.
It will be instructive to see your results with a 30dB attenuator
in-line and using the suggested tx_waveforms test.
*From:*Marcus D Leech <patchvonbr...@gmail.com>
*Sent:* Thursday, March 25, 2021 3:40 PM
*To:* Jerrid Plymale <jerrid.plym...@canyon-us.com>
*Cc:* USRP-users@lists.ettus.com
*Subject:* Re: [USRP-users] Strong noise added to signal transmitted
by X310 with a UBX 40 daughterboard
Could you confirm that you’re using at least 30dB of attenuation in
the coax link?
Sent from my iPhone
On Mar 25, 2021, at 6:27 PM, Jerrid Plymale
<jerrid.plym...@canyon-us.com
<mailto:jerrid.plym...@canyon-us.com>> wrote:
Yes, moving TX out of the RX band has no affect on the noise level
increase.
Best Regards,
Jerrid
*From:*Marcus D Leech <patchvonbr...@gmail.com
<mailto:patchvonbr...@gmail.com>>
*Sent:* Thursday, March 25, 2021 2:29 PM
*To:* Jerrid Plymale <jerrid.plym...@canyon-us.com
<mailto:jerrid.plym...@canyon-us.com>>
*Cc:* USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com>
*Subject:* Re: [USRP-users] Strong noise added to signal
transmitted by X310 with a UBX 40 daughterboard
If you move the TX out of band with respect to the RX do you still
see the noise when the TX graph starts?
Sent from my iPhone
On Mar 25, 2021, at 3:57 PM, Jerrid Plymale
<jerrid.plym...@canyon-us.com
<mailto:jerrid.plym...@canyon-us.com>> wrote:
So I was able to test setting up both USRPs with the same 10
MHz reference signal, and there was no improvement to the
noise being added.
If the flowgraph just emits a CW tone, we see a similar
response, the added noise is still there and at the same
level, we just have the added spike of the CW tone at the
frequency we set it to.
Best Regards,
Jerrid
*From:*Marcus D Leech <patchvonbr...@gmail.com
<mailto:patchvonbr...@gmail.com>>
*Sent:* Wednesday, March 24, 2021 5:01 PM
*To:* Jerrid Plymale <jerrid.plym...@canyon-us.com
<mailto:jerrid.plym...@canyon-us.com>>
*Cc:* USRP-users@lists.ettus.com
<mailto:USRP-users@lists.ettus.com>
*Subject:* Re: [USRP-users] Strong noise added to signal
transmitted by X310 with a UBX 40 daughterboard
You don’t need 1PPS for this. Having an external high quality
reference may help, assuming my guess about your issue is
correct.
What happens if your flow graph just simply emits a Cw tone,
using the mute function perhaps tied to a GUI control or some
such.
Sent from my iPhone
On Mar 24, 2021, at 7:13 PM, Jerrid Plymale
<jerrid.plym...@canyon-us.com
<mailto:jerrid.plym...@canyon-us.com>> wrote:
Ok, if that’s the case, would it help to have both USRPs
connected to the same 10 MHz reference signal and PPS? In
this situation, would I need to provide a secondary source
for the PPS, or can that use the 10 Mhz reference as well?
Best Regards,
Jerrid
*From:*Marcus D. Leech <patchvonbr...@gmail.com
<mailto:patchvonbr...@gmail.com>>
*Sent:* Wednesday, March 24, 2021 2:23 PM
*To:* Jerrid Plymale <jerrid.plym...@canyon-us.com
<mailto:jerrid.plym...@canyon-us.com>>
*Cc:* USRP-users@lists.ettus.com
<mailto:USRP-users@lists.ettus.com>
*Subject:* Re: [USRP-users] Strong noise added to signal
transmitted by X310 with a UBX 40 daughterboard
On 03/24/2021 05:10 PM, Jerrid Plymale wrote:
The devices are operating using direct connection via
coax cables.
You absolutely need to put a 30dB attenuator in-line to
prevent RX destruction in the case of "ooops" moments from
setting the TX
power output too high.
The target frequency is 1.57542 GHz, and our current
bandwidth is 4 MHz. We will need to increase the
bandwidth to 20 MHz soon for further system development.
The TX and RX gain are maxed on the receiving
hardware. The TX gain of the transmitting hardware is
set to 0, as at max the noise strength increases to ~
20 dB.
Attached are images of the FFT provided by the
Frequency Sink in Gnuradio. Hopefully these give a
visual aid for the problem at hand. When I have the
transmitter USRP turned off (image 1), it would seem
like the noise floor coming into the USRP is around
-94 dB. When the transmitter is turned on and the
flowgraph is started with the transmitted signal muted
(I am using a python block with code to create custom
signals that is then connected to a mute block that
then connects to the UHD USRP sink block to be able to
mute the signal during runtime), the noise floor
increases to around -78 dB.
Best Regards,
Jerrid
You are likely just seeing the LO leakage, along with the
inevitable phase-noise curve of the LO.
*From:* Marcus D Leech <patchvonbr...@gmail.com>
<mailto:patchvonbr...@gmail.com>
*Sent:* Wednesday, March 24, 2021 11:58 AM
*To:* Jerrid Plymale <jerrid.plym...@canyon-us.com>
<mailto:jerrid.plym...@canyon-us.com>
*Cc:* USRP-users@lists.ettus.com
<mailto:USRP-users@lists.ettus.com>
*Subject:* Re: [USRP-users] Strong noise added to
signal transmitted by X310 with a UBX 40 daughterboard
Is the j B is over-the-air or direct connection?
What frequency? Bandwidth?
Do you have TX and RX gain turned all the way up?
Can you share your flow-graphs, or minimum
Graphs that show the problem?
Sent from my iPhone
On Mar 24, 2021, at 12:20 PM, Jerrid Plymale
<jerrid.plym...@canyon-us.com
<mailto:jerrid.plym...@canyon-us.com>> wrote:
Hello All,
I have been running tests in which I am
transmitting a signal from one USRP X310 that’s
using a UBX 40 daughterboard, and that signal is
being received by another USRP X310 using a UBX 40
daughterboard. I have noticed that when I have the
receiving USRP running with the Gnuradio flowgraph
active, as soon as I start the transmitting USRP’s
Gnuradio flowgraph, there is a jump in the noise
floor as it is seen by the receiving USRP, and its
roughly a 14 dB increase. This occurs even if I
have the signal being transmitted muted. Does
anyone have any idea what the source of this added
noise could be? It is something that I need to
mitigate as much as possible for the tests I am
running using these USRPs. Any feedback will be
greatly appreciated, thanks!
Best Regards,
Jerrid
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