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Hi Jeff;

Per my post:
@ Gary O'Neil - /g/nanovna-users/message/9184

I don't find any source of disagreement in your posts:
@ Jeff Anderson - /g/nanovna-users/message/9178
@ Jeff Anderson - /g/nanovna-users/message/9181

I will also confess that I overstated a Hackborn quote which modified
its more accurate interpretation. He didn't dismiss anything, but
rather makes the statement that all of the errors and uncertainties in
the system are measured and remembered.

By that inexcusable but excellent example of my inability to make and
defend my point; I will attempt instead to understand your
understanding of the process, and search for where the two will
hopefully converge.

After several reads and re-reads of your and Erik's posts; I think you
two may be on the same page. Your post, and another by Dr. Kirby:
@ Dr. Kirby - /g/nanovna-users/message/9183

hint at a possible disconnect in "my" understanding, which may be
linked to a vagueness in the use of jargon, or more pathetically, my
lack of understanding of the jargon in use.

The way I am interpreting your posts, I see the use of the terms
calibration, characterization, and correction. You also identify the
noise and imperfect characterizations of the standards as not being
corrected by the error correction process.... referring to a Hand
quote.

You also make reference to HP and Keysight quotes... both of which I
agree with as being correct. To my point; any statement that the
"accuracy" of something (anything) used for the purpose of improving
the accuracy of the measurement must itself be accurate cannot be
argued. It is made true by the way it is stated and/or presented.

Clearly there is no argument that even with the highest of quality in
the standards, at some upper limit of frequency, the manufacture of
standards sets to the exacting dimensional tolerances required to
guarantee that the reference plane remains constant becomes
unachievable, significant rotational errors occur and corrections for
the known and well defined imperfections are needed in the calibration
in order to make meaningfully accurate measurements.

So my lack of understanding seems to lie in the question being what's
the point of attempting to model imperfect standards of uncertain
accuracy, and using that model to corrupt the ability of the algorithm
to accurately measure and remember all of the system errors and
uncertainties with uncertain guesses at what the ones that are measured
have been characterized to be? Are not the errors that manifest
themselves as problematic, only problematic because they result from
differences in the location of their respective reference planes? the
uncertainties of the parasitic reactance properties associated with
each of the standards are measurable, and thus they will be "measured
and remembered". As such, they are all present and accounted for in the
calibration. Characterization of the standard reference plane location
(degrees per GHz) would seem to be a more precise and accurate manner
to compensate (not calibrate) for their respective rotational offsets
without compromising the integrity of the calibration algorithm. After
that; how precise does the rotational compensation need to be in order
to sufficiently orient the regions of infinity to the VNA user such
they are presented with the most accurate measurement the VNA is
capable of providing?

This brings up yet another question. If the devices are "measured and
remembered" as the math clearly dictates, what would cause a short and
an open (defined as such) to appear anywhere other than the locations
-1 and 1 without biasing the algorithm to place them differently? If
they are intentionally placed at a different location, what is the
justification for doing so, since this would seem to create a need to
compensate for the induced post calibration offset errors ?


--
73

Gary, N3GO

KV5R,

They are the handout for the courses on antenna and feedlines.
As such they are often read this, evaluate this question.

If your going to suck those files up, then get the books that go with them
as many
do reference them for reading. If not you are just wasting disk space.

Allison
-----------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

Robert,

It would be desirable if you could also measure the transmission through
the
cable, including both magnitude and phase versus frequency. Plus any info
you have about the supposed characteristic impedance and velocity factor of
the cable. Extend the lower frequency limit down to 50 kHz as well.

A second set of equivalent plots but with the nano's scan set for a span
of about
10 MHz and a center frequency well up in the VHF regime (~150 MHz would be
fine) might also be pretty informative. These should also include the
scan of the
termination that you're using by itself.

The overall shape of the plot is somewhat consistent with two point
reflections
of roughly equal magnitude, separated in round-trip time by a bit under
500 nsec.
However, the deteriorating overall return loss at increasing frequency is
not really
consistent with that simple model. But if your connections to the hard
line were
a bit crude, creating added impedance bumps at the two ends, the curve
I've seen
so far would be better-explained.

Could you also send a photo showing exactly how you are physically
interfacing
to the hard line from the small cable environment?

What I've seen so far suggests a cable whose impedance is not really 50
ohms,
combined with some other issue such as (perhaps) impedance bumps at the two
ends. The period of ~2 MHz seen in the S11 plot is not consistent with
a physical
length of 350 ft- in fact it's off by almost a factor of 2 if one assumes
a VF of 0.67.

Dana K8YUM

はぁ (ha), that did the trick. I did the surgery on only one leg so there is still some imbalance, but the directivity improved from 8dB to 16dB, on par with the performance with tuning (see attached). Don't think I'll ever convince TOKO or mini-circuits to build baluns vertically like this though, and it won't fit in the shield can anymore, so I think the tuning will stay for now.

I just tried the TC1-1-13M on two units. With a balanced (symmetrical) bridge circuit (like the one in v2_0) the directivity is not good, around 8 to 10dB up to 3GHz, but just out of curiosity I tried it on a new unit (v2_2) that has the 0.3pF tuning, and the directivity graph turned out nearly identical as before with the old balun (TOKO 617DB-1023=P3), with 17dB worst directivity. Looking at the pictures it seems to have the same physical asymmetry as the 617DB-1023=P3 (see attached), but the good news is this tuning seems to be applicable to more than one manufacturer's baluns, so I can have a second source just in case.

I'm not sure why the simulation doesn't match measurements, but it might be that the asymmetry isn't accounted for because the balun was never intended for this use case ;) The model probably accurately predicts CMRR, but doesn't predict "Common Mode to Differential Mode transfer".

Port 00 or Port 01, that used for one-port measurement of s11, may not be a
good 50+j0 source over your frequency range. You exhibit everywhere better
than 15 dB return loss which is pretty good, but the periodicity of the
measurement is a bit disturbing.

Try recalibrating and remeasuring with a 6 dB attenuator on the s11 port.
That will assure a return loss in excess of 12 dB and stabilize the
impedance of that port.

Dave - W?LEV

On Mon, Jan 6, 2020 at 12:28 AM Robin Midgett <K4IDC@...> wrote:

I've calibrated my NanoVNA & connected it to an approximate 350' length of
coax with a known good dummy load on the opposite end. The S11 plot is
attached...not pleasing at all.
Can anyone on the list say what the cause may be?
I have ideas, but I don't want to sway anyone's opinion..

--

*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*