A 3dB attenuation will really improve the reflection coefficient. Using this calculator http://www.rfcafe.com/references/calculators/vswr-return-loss-conversion-calculator.htm you can see that a 3 dB attenuation will improve a 3:1 VSWR to 1.7:2, or a 6 dB return loss to 12 dB, so you've really improved the match. The gory details of noise figure and match are in here http://literature.cdn.keysight.com/litweb/pdf/5952-3706E.pdf and Keysight has a spreadsheet to do the calculations here https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=96887&nid=-34815.0.00&id=96887 (Probably more detail than needed)
Did you add the 3dB attenuator to the noise figure? Dave On Sat, Feb 3, 2018 at 10:41 AM, Dan CaJacob via USRP-users <usrp-users@lists.ettus.com> wrote: > I saw no improvement when including a 3dB 50 Ohm attenuator as part of the > B200 NF meter. I guess I could try higher attenuator values. > > On Thu, Feb 1, 2018 at 9:16 PM Dan CaJacob <dan.caja...@gmail.com> wrote: >> >> I was gonna say, there's actually three of them ;) >> >> >> On Thu, Feb 1, 2018, 9:06 PM Robin Coxe via USRP-users >> <usrp-users@lists.ettus.com> wrote: >>> >>> On p.8 of B200 schematic: >>> T801 is Macom ETC1-1-13TR (RF2) >>> T800 is Minicircuits TC1-1-43A+ (RF3) >>> U802 is Anaren BD3150L50100AHF (RF1) >>> >>> On Thu, Feb 1, 2018 at 5:45 PM, Ron Economos via USRP-users >>> <usrp-users@lists.ettus.com> wrote: >>>> >>>> There's also a balun on the AD9361 input. Unfortunately, the balun part >>>> number for the low frequency path is not on the schematic. >>>> >>>> Ron >>>> >>>> On 02/01/2018 05:39 PM, Dan CaJacob via USRP-users wrote: >>>> >>>> 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 >>>> >>>> >>>> _______________________________________________ >>>> USRP-users mailing list >>>> USRP-users@lists.ettus.com >>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>>> >>>> >>>> >>>> _______________________________________________ >>>> USRP-users mailing list >>>> USRP-users@lists.ettus.com >>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>>> >>> >>> _______________________________________________ >>> USRP-users mailing list >>> USRP-users@lists.ettus.com >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> >> >> -- >> Very Respectfully, >> >> Dan CaJacob > > -- > Very Respectfully, > > Dan CaJacob > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
