Is the basic OSL calibration sufficient? Or do I need to do something special?
Peter
toggle quoted message
Show quoted text
On Aug 7, 2019, at 11:18 AM, tuckvk3cca <tuckvk3cca@...> wrote:
I don't understand you Peter, the 8753 is a network analyzer, which will
give you S11 the reflection coefficient. The log of its magnitude will be
the return loss. It should be able to convert your readings into complex
impedance R+jX too. I have the equivalent of the minivNA which only
calibrates with one point, an open load. I still get 38 to 40 dB return loss
at HF for some of my better 50ohm loads. I use the j-VNA software which
converts all magnitudes and phase measurements to S parameters of R+jX etc.
Most of the time I just live with this simple calibration procedure. On
transmission just a through pass for baseline calibration works for most
applications. For a full S parameter set measurement one does need to work
much harder in terms of calibration.
-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Peter
Gottlieb
Sent: Wednesday, August 7, 2019 4:29 PM
To: [email protected]
Subject: Re: [nanovna-users] Some basic load measurements
If you can tell me a simple way to set up to measure return loss I can do
that for the various loads. I can do the smith chart but it is very hard to
see in a photo as the loads are all just tiny dots near the center on the
horizontal line. Perhaps easier to see if I change display colors or save
onto the floppy instead. What I call the cheap BNC is an old mil spec
terminator probably designed for HF and it gives a nice little spiral around
the center.
Peter
On Aug 7, 2019, at 5:48 AM, tuckvk3cca <tuckvk3cca@...> wrote:
That is expected Peter. Have you got the imaginary parts or phases? Best
to plot on a Smith chart too and see how your samples rotate from low to
high frequency. 1.02 swr corresponds to about 40dB return loss which is
very respectable at 900MHz.Sent from my Samsung Galaxy smartphone.
-------- Original message --------From: Peter Gottlieb
<hpnpilot@...> Date: 07/08/2019 04:43 (GMT+01:00) To:
[email protected] Subject: [nanovna-users] Some basic load
measurements Resending from website as it didn't seem to go through as a
message. Also my pasted table from Excel lost formatting so I tried to fix
it to be more readable.I just did some very simple resistance and SWR
measurements using a HP 8753ES with 85046A, resistance was measured using a
calibrated Agilent 34401A in 4 wire mode.I did a very basic one port 3 point
cal using a Anritsu OSL which is specified to over 3 GHz.I took measurements
at 900 MHz.Load R ohms SWR SWR notesOSL
50.052 1.001 FlatCheap BNC 51.104 1.908
Sloping up with freqNano load 49.044 1.019
FlatNarda 12.4 GHz 49.536 1.018 FlatTiny SMA
50.787 1.009 FlatI am guessing there is some significant
reactive component in the BNC terminator. All three of the SMA loads showed
a flat SWR with frequency so I'm thinking they all have a minimal reactive
component.The difference in resistances while keeping SWR low was a bit of a
surprise to me. The load that came with the Nano is over an ohm off of the
load I used to calibrate yet the SWR remains at a low 1.019. Why is this? I
did the math and surprisingly this is indeed correct, per calculation the
SWR should be 1.021 vs my measured 1.019. I'd say this is darn close seeing
one measurement is DC resistance and the other is at 900 MHz.So my
conclusion is that SWR is not a sensitive number to see resistance
differences.Once I read some of the references cited I can do some more
advanced measurements.Peter
