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
<mailto: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 <mailto: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
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--
Very Respectfully,
Dan CaJacob
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