That's an interesting thought. The 9361 does have a pretty bad match. I'll try adding a 50 Ohm attenuator and see if that helps.
On Thu, Feb 1, 2018 at 5:14 PM Robin Coxe <robin.c...@ettus.com> wrote: > Hi Dan. Both the B200 and the E312 use the Analog Devices AD9361 RF > integrated transceiver. This chip does have an integrated LNA. Perhaps > there's some sort of mismatch between your DUTs and this integrated LNA at > <1 GHz? > > ADI publishes the RX S-parameters: > https://ez.analog.com/thread/41208#137929 > > -Robin > > On Thu, Feb 1, 2018 at 7:46 AM, Dan CaJacob via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> Hey guys, >> >> I have put together a noise figure meter application that uses a USRP as >> the sensing device. It started off as a way to measure the NF of the USRP >> itself. I have a calibrated noise source from an HP 8970B Noise Figure >> Meter. To test the NF of the USRP, I connect the head to the USRP input. My >> GNURadio flowgraph maximizes the USRP gain and measures a moving average of >> the received power while I switch the noise source on and off. The >> difference in the received power level, in addition to the ENR table from >> the noise source, can then be used to calculate the NF of the USRP itself >> using the y-factor method. >> >> Once you have the NF for the USRP at many frequencies (I test every 50 >> MHz from 50 MHz - 6000 MHz), you can modify the same procedure to test the >> NF of a Device Under Test (DUT) which is connected between the noise source >> and the (now calibrated) USRP. You can use the USRP cal table we generated >> in the previous step to derive the NF of the DUT corrected for the NF of >> the USRP. >> >> In short, this all works incredibly well and garners very repeatable >> results. One complication is that you will see wild NF at certain >> frequencies due to local interference like LTE and WIFI. I've also compared >> the results to that which the HP device measures and they're very >> comparable. ... Except below ~ 1GHz. >> >> And here's the issue - I am seeing higher NF for DUTs below about 1GHz >> and particularly worse below 500 MHz. I was hoping someone at Ettus might >> be able to shed some light on why this might be. Curiously, the USRPs NF >> doesn't seem to be too bad, just the DUT. >> >> I'll note that I am nominally using a B200 for these tests, but I also >> tried an E312 just in case the filter banks might help out somehow. I >> didn't see a difference - they both had the same problem. >> >> I have used several DUTs for this test, including LNA boards we have >> designed ourselves and a Mini-Circuits ZX60-P103LN+ ( >> https://www.minicircuits.com/pdfs/ZX60-P103LN+.pdf). Both seem to >> exhibit higher NF when measured with a USRP below 1 GHz. When testing them >> on the HP NF meter, the NF is as expected all the way down to 50 MHz. >> >> I have attached the B200 cal data for your enjoyment as well as the >> B200-measured ZX60 NF and the HP-measured ZX60. The HP NF meter only goes >> up to 1600 MHz, which is why that data file stops there. I was surprised to >> see the B200 seemed to have a better NF than the E312, which averaged 8 dB >> NF, by the way. >> -- >> Very Respectfully, >> >> Dan CaJacob >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> > -- Very Respectfully, Dan CaJacob
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