Hi Altug, hi Patrick, The explanations by Patrick make sense to me. The MMPX connectors were required to fit the available space, although they may not be as rigid as the SMAs unfortunately.
The power question is as follows: To use the full amplitude in the tx_waveforms example you need to pass an amplitude value of sqrt(2), so roundabout 1.4142. This should get you closer to our numbers. The FPGA image should not make a difference when using the same rates. For the KB article you're right and I just updated it. Most of our USRPs are safe if you put the attenuator between TX and RX, but the X440 should not be able to destroy itself even without this. /Martin From: Kaya, Altug <altug.k...@hhi.fraunhofer.de> Sent: Monday, August 5, 2024 12:40 PM To: Panuski, Patrick <patrick.panu...@str.us>; usrp-users@lists.ettus.com Subject: [USRP-users] Re: X440 Tx and Rx Power Constraints Hi Patrick, Thank you for your detailed answer based on your experience. Please find my last, and probably the final, findings about this topic. 1. I checked the MMPX connection once again. It is definitely not the best type of connector if your setup consists of SMA-type attenuators/analog filters. They might bend the MMPX-to-SMA cable around and cause lose connections, you are right. In addition, the MCR was set to 368.64 MHz in order to set a converter rate of 2.94912 MHz. Furthermore, instead of measuring the power of the constant wave at 500 MHz with a marker of the spectrum analyzer, I started to use a Power Meter from Rohde & Schwarz to consider the contribution of aliases due to having a RF Sampling device. Moreover, I used two different X440's and their 2 possible Tx ports (4 ports in total due to CG_1600 image) to eliminate port specific problems. Unfortunately, I still measure around -5.2 dBm instead of around -2 dBm dBm (according to this graph given for 2.94912 GSps https://www.ni.com/docs/de-DE/bundle/ettus-usrp-x440-specs/page/specs.html#:~:text=Figure%202.%20TX%20Maximum%20Output%20Power%3A%200%20dBFS%20CW%2C%202.94912%20GSps%20Converter%20Rate%2C%200%20Hz%20Waveform%20Frequency). Apparently, I have to live with the current status of this setup. 1. I agree. An update on the knowledge base page (https://kb.ettus.com/USRP_X410/X440_Getting_Started_Guide#:~:text=X440%3A%20Always%20use%20at%20least%2030dB%20attenuation%20if%20operating%20in%20loopback%20configuration) can certainly clear this confusion. From: Panuski, Patrick <patrick.panu...@str.us<mailto:patrick.panu...@str.us>> Sent: Thursday, August 1, 2024 8:31 PM To: Kaya, Altug <altug.k...@hhi.fraunhofer.de<mailto:altug.k...@hhi.fraunhofer.de>>; usrp-users@lists.ettus.com<mailto:usrp-users@lists.ettus.com> Subject: RE: X440 Tx and Rx Power Constraints Hi Altug, 1. Have you tried setting your converter rate to 2.94912 GHz and comparing to the Ettus graph to get an apples-to-apples comparison? Also in my experience, a weak MMPX connection can cause at least a 3dB loss... You can sometimes see the observed Tx power jump around when you wiggle or adjust the connectors. My X440 currently has one transmit channel that transmits about 3 dB less power than the others, and I think I've narrowed this down to the particular MMPX connector on that channel being weak/faulty. I'd suggest trying a different cable and also testing transmission on other channels, but overall I wouldn't be surprised if the different clock rate was having an effect here. 2. On the X440, you're probably okay directly connecting Tx to Rx. I think the 30 dB attenuator recommendation is left over from older USRP devices and is less applicable to the X440 architecture. The older USRPs had separate RF front ends with amplifiers on the transmit side and LNAs on the receive side that could be individually controlled in software, so it was possible to set transmit/receive gains too high for a loopback configuration and the device could damage itself. With a 30 dB attenuator, virtually no software settings could make the device damage itself in a loopback configuration. However on the X440, the entire front end is integrated into the RFSoC and the daughter card is now just a passthrough. This means that your UHD program cannot change amplifiers and gains so the max transmit power will be capped in hardware around 0 dBm which is significantly below the sustained Rx damage threshold. 3. Disclaimer: I'm not an expert here, just a user Thanks, Patrick From: Kaya, Altug <altug.k...@hhi.fraunhofer.de<mailto:altug.k...@hhi.fraunhofer.de>> Sent: Wednesday, July 31, 2024 5:57 AM To: usrp-users@lists.ettus.com<mailto:usrp-users@lists.ettus.com> Subject: [USRP-users] X440 Tx and Rx Power Constraints *** WARNING: This message originates from outside the STR organization. *** *** Please take appropriate care in opening any links or attachments. *** Dear USRP Mailing List Members, I have two questions regarding power constraints of X440: 1. I set the master clock rate to 360 MHz and made sure that the converter rate becomes 2.88 GSps instead of 1.44 GSps. I used an UHD example called "tx_waveforms" to verify the maximum output power. To compare the results with the specification sheet, a constant ('CONST') wave of 500 MHz frequency with an amplitude of 1 is used. While expecting a single tone whose power is around -2 dBm (according to this graph given for 2.94912 GSps https://www.ni.com/docs/de-DE/bundle/ettus-usrp-x440-specs/page/specs.html#:~:text=Figure%202.%20TX%20Maximum%20Output%20Power%3A%200%20dBFS%20CW%2C%202.94912%20GSps%20Converter%20Rate%2C%200%20Hz%20Waveform%20Frequency), it is around -5 dBm. Does the output power vary that much between the converter rates of 2.94912 GSps and 2.88 GSps? 1. I will use another X440 to capture the single tone (and the aliases due to RF sampling) and analyze the ADC spurs. On the front panel, maximum receiver input power is stated as 10 dBm. This is further elaborated down to the operational frequency in this webpage (https://www.ni.com/docs/de-DE/bundle/ettus-usrp-x440-specs/page/specs.html#:~:text=Maximum%20input%20power%2C%20damage%20level). On the other hand, in the loop back configuration, >30dB attenuation between ports were recommended. What is the difference between connecting the Tx port of one X440 to the Rx port of another X440 and connecting Tx&Rx ports of different daughter boards of the same X440? Why does the maximum receiver power requirement change? The maximum one can transmit from a Tx port of X440 is 0 dBm. According to my understanding, it should be safe to connect Tx and Rx ports (of either same or different X440s) to each other as long as I am working with a constant waveform with a PAPR of 0 dB. I am grateful for your time and effort. If anything is unclear and you are willing to help, I can provide further details. Best regards, Altug KAYA National Instruments Dresden GmbH; Gesch?ftsf?hrer (Managing Directors): Sabrina Gilman, Kathleen Heard Spurck, Carl Schumacher; 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.
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