Yep, I am aware of that document and I am using the Y-factor method. The 3 dB attenuator was calibrated with the B200 - i.e. I measured the NF of the USRP + 3dB attenuator as a system. That data then serves as the calibration data to correct for it's contribution to the subsequent NF measurement of the B200 + 3dB pad + DUT.
I saw the same poor performance below 1 GHz when using the 3dB pad. On Sun, Feb 4, 2018 at 11:44 AM David Bengtson <david.bengt...@gmail.com> wrote: > 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 > > > -- Very Respectfully, Dan CaJacob
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