开云体育

On Wed, 19 Aug 2020 at 00:04, Dana Whitlow <k8yumdoober@...> wrote:

I couldn't figure out who from the morass of comments,

but somebody wrote

"It’s not that important that the phase of the open and short are exactly

180 degrees apart".



This is true only if the calibration routines know about this! Otherwise

all bets are off. And the only way for the routines to know about this is

through the cal stds definitions table for that physical set of standards.



Dana

Even if the standards are 180 degrees apart in phase, the calibration
routines need to know the exact phases at each frequency. +100 degrees and
-80 are significantly different from +110 degrees and -70 degrees, yet both
differ by exactly 180 degrees.

In any case, it is impossible to keep the phases 180 degrees apart at all
frequencies. A polynomial is used to express the fringing capacitance of
the open and sometimes the inductance of a short too, although the
inductance of the short is a significantly smaller effect.

--

Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

I have been gone for a few weeks. Where did the downloads for OneOfEleven go? I went to he old GitHub link and it is broken.

Gary

On 8/18/20 5:02 PM, Jim Lux wrote:

On 8/18/20 4:10 PM, AA7US wrote:

I’ve searched for hours and so far come up empty handed...

Does anyone have a suggestion for a soft, clamshell style, padded storage case that'll fit a NanoVNA-H4 with enough extra room for typical accessories?? It needs to have a separate inner zippered compartment to store the calibration fittings and coax jumpers so they won’t rattle around and rub on the NanoVNA's screen.

I've seen multimeter storage cases which are close, but they're either way too big or lack a zippered internal storage compartment.? A portable hard drive case might work also, but again, every one I've encountered lacks an internal zippered storage compartment.

Ideally being able to buy from Amazon or eBay would be best.

In addition to the suggestions in my last email...
There are a wide variety of soft sided cases made for portable games (your Nintendo Switch, for instance) with pockets for adapters, games, etc.
-=-

or a portable hard drive case:



zillions of cases in every size and configuration you can imagine... You can have it tomorrow in most cases.

On 8/18/20 4:10 PM, AA7US wrote:

I’ve searched for hours and so far come up empty handed...
Does anyone have a suggestion for a soft, clamshell style, padded storage case that'll fit a NanoVNA-H4 with enough extra room for typical accessories? It needs to have a separate inner zippered compartment to store the calibration fittings and coax jumpers so they won’t rattle around and rub on the NanoVNA's screen.
I've seen multimeter storage cases which are close, but they're either way too big or lack a zippered internal storage compartment. A portable hard drive case might work also, but again, every one I've encountered lacks an internal zippered storage compartment.
Ideally being able to buy from Amazon or eBay would be best.

In addition to the suggestions in my last email...


There are a wide variety of soft sided cases made for portable games (your Nintendo Switch, for instance) with pockets for adapters, games, etc.

On 8/18/20 4:10 PM, AA7US wrote:

I’ve searched for hours and so far come up empty handed...
Does anyone have a suggestion for a soft, clamshell style, padded storage case that'll fit a NanoVNA-H4 with enough extra room for typical accessories? It needs to have a separate inner zippered compartment to store the calibration fittings and coax jumpers so they won’t rattle around and rub on the NanoVNA's screen.
I've seen multimeter storage cases which are close, but they're either way too big or lack a zippered internal storage compartment. A portable hard drive case might work also, but again, every one I've encountered lacks an internal zippered storage compartment.
Ideally being able to buy from Amazon or eBay would be best.

Check out Pelican cases, they have some fairly small ones.

Another source is Cabela's (or Walmart, perhaps) - a small gun case might work.

Both of those will typically have foam inserts that you cut as you need. The Pelican ones are prescored as 1/2" cubes, so you just pluck out the ones to make the right size holes.

Those are likely to be hard sided. The softer sided ones - The ones I've used have been for things like CDs or headphones. You might try something like Guitar Center's online store in the accessories. Or an auto supply place like PepBoys, Kragen, AutoZone. They often have cases of various sizes to store stuff in.

And finally, places lie U-Line sells all manner of shipping and factory organizing stuff, and some of it is storage containers.

(You might find something for the medical industry, but it will be wretchedly expensive)

Not soft, and you'd need to provide your own padding.
But if interested in that retro look, search for "empty cigar box" on ebay.
If not considered appropriate for a nanoVNA,
could use it for your grid dip meter.

I'd probably just steal some tupperware-ish thing out of the kitchen.

Jerry, KE7ER

While they don't have a zippered area, they do have plenty of room for all the goodies and can be customized with a pre-cut foam section that lets you take out pieces to fit items.

Check these out at Harbor Freight


Some stores also have some bigger units that are plastic and seal air/water tight. I think they are around $40 or so.

Take Care & 73
de KC6UFM
Charles

I’ve searched for hours and so far come up empty handed...

Does anyone have a suggestion for a soft, clamshell style, padded storage case that'll fit a NanoVNA-H4 with enough extra room for typical accessories? It needs to have a separate inner zippered compartment to store the calibration fittings and coax jumpers so they won’t rattle around and rub on the NanoVNA's screen.

I've seen multimeter storage cases which are close, but they're either way too big or lack a zippered internal storage compartment. A portable hard drive case might work also, but again, every one I've encountered lacks an internal zippered storage compartment.

Ideally being able to buy from Amazon or eBay would be best.

Thanks in advance,

John
AA7US

I couldn't figure out who from the morass of comments,
but somebody wrote
"It’s not that important that the phase of the open and short are exactly
180 degrees apart".

This is true only if the calibration routines know about this! Otherwise
all bets are off. And the only way for the routines to know about this is
through the cal stds definitions table for that physical set of standards.

Dana

On 8/18/20 1:15 PM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:

On Tue, 18 Aug 2020 at 16:28, Jerry Gaffke via groups.io <jgaffke=
[email protected]> wrote:

David,

Having O-S-L correction factors only available in host software like
nanovna-saver

Not if you want to take the unit mobile and use it without a computer,
which for me at least is the big attraction of a NanoVNA.
Jerry, KE7ER

If I want a laboratory, I own two HP ones, have access to a PNA-X. (I also
have a VNWA which I have never used) The big attraction to me for the
NanoVNA is its portability, and that gets lost if you have to hook it up to
external software.
Everyones uses are different. But IMHO, the thing the NanoVNA lacks most is
any sensible form of calibration, in the firmware. That would require one
to enter calibration kit parameters.

And is probably a non trivial modification - you'd need a UI for entering and editing the parameters, a UI to select them (not so tough), and a way to preserve them across power cycles.




In main.c (working from hugen's repo), here's probably where you need to fool with it..


static void apply_error_term_at(int i)
{
// S11m' = S11m - Ed
// S11a = S11m' / (Er + Es S11m')
float s11mr = measured[0][i][0] - cal_data[ETERM_ED][i][0];
float s11mi = measured[0][i][1] - cal_data[ETERM_ED][i][1];
float err = cal_data[ETERM_ER][i][0] + s11mr * cal_data[ETERM_ES][i][0] - s11mi * cal_data[ETERM_ES][i][1];
float eri = cal_data[ETERM_ER][i][1] + s11mr * cal_data[ETERM_ES][i][1] + s11mi * cal_data[ETERM_ES][i][0];
float sq = err*err + eri*eri;
float s11ar = (s11mr * err + s11mi * eri) / sq;
float s11ai = (s11mi * err - s11mr * eri) / sq;
measured[0][i][0] = s11ar;
measured[0][i][1] = s11ai;

// CAUTION: Et is inversed for efficiency
// S21m' = S21m - Ex
// S21a = S21m' (1-EsS11a)Et
float s21mr = measured[1][i][0] - cal_data[ETERM_EX][i][0];
float s21mi = measured[1][i][1] - cal_data[ETERM_EX][i][1];
float esr = 1 - (cal_data[ETERM_ES][i][0] * s11ar - cal_data[ETERM_ES][i][1] * s11ai);
float esi = - (cal_data[ETERM_ES][i][1] * s11ar + cal_data[ETERM_ES][i][0] * s11ai);
float etr = esr * cal_data[ETERM_ET][i][0] - esi * cal_data[ETERM_ET][i][1];
float eti = esr * cal_data[ETERM_ET][i][1] + esi * cal_data[ETERM_ET][i][0];
float s21ar = s21mr * etr - s21mi * eti;
float s21ai = s21mi * etr + s21mr * eti;
measured[1][i][0] = s21ar;
measured[1][i][1] = s21ai;
}


and here, after the measurements are made, where the measurements are turned into cal parameters.



void cal_done(void)
{
chMtxLock(&mutex_sweep);
ensure_edit_config();
if (!(cal_status & CALSTAT_LOAD))
eterm_set(ETERM_ED, 0.0, 0.0);
//adjust_ed();
if ((cal_status & CALSTAT_SHORT) && (cal_status & CALSTAT_OPEN)) {
eterm_calc_es();
eterm_calc_er(-1);
} else if (cal_status & CALSTAT_OPEN) {
eterm_copy(CAL_SHORT, CAL_OPEN);
eterm_set(ETERM_ES, 0.0, 0.0);
eterm_calc_er(1);
} else if (cal_status & CALSTAT_SHORT) {
eterm_set(ETERM_ES, 0.0, 0.0);
cal_status &= ~CALSTAT_SHORT;
eterm_calc_er(-1);
} else {
eterm_set(ETERM_ER, 1.0, 0.0);
eterm_set(ETERM_ES, 0.0, 0.0);
}

if (!(cal_status & CALSTAT_ISOLN))
eterm_set(ETERM_EX, 0.0, 0.0);
if (cal_status & CALSTAT_THRU) {
eterm_calc_et();
} else {
eterm_set(ETERM_ET, 1.0, 0.0);
}

cal_status |= CALSTAT_APPLY;
redraw_request |= REDRAW_CAL_STATUS;
chMtxUnlock(&mutex_sweep);
}

50 years ago: PCAP with punch card decks....;-)

Dave,

Thanks.
This had been strictly an academic exercise.
It is now something to file under "Why short HF whips are so inefficient"

I need to start playing with one of the antenna simulation programs someday.
The tools available now (software simulations, nanoVNA, tinySA, DSP receivers,
cheap surface mount parts and board fab, linux on a $100 chromebook)
make it all way easier to play with than it was 50 years ago.

Jerry, KE7ER

The internal software doe not have not have that cal standard set in it.
The side effect is the user then has to "do the math" and adjust as needed.
Tedious but still better than not having anything.

The down side is you have to understand what you have and how best
to exploit it.

At HF its less significant and even at 400mhz its not so bad.

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

On Tue, 18 Aug 2020 at 16:28, Jerry Gaffke via groups.io <jgaffke=
[email protected]> wrote:

David,

Having O-S-L correction factors only available in host software like
nanovna-saver

Not if you want to take the unit mobile and use it without a computer,
which for me at least is the big attraction of a NanoVNA.

Jerry, KE7ER

If I want a laboratory, I own two HP ones, have access to a PNA-X. (I also
have a VNWA which I have never used) The big attraction to me for the
NanoVNA is its portability, and that gets lost if you have to hook it up to
external software.

Everyones uses are different. But IMHO, the thing the NanoVNA lacks most is
any sensible form of calibration, in the firmware. That would require one
to enter calibration kit parameters.

If you are only working at HF, it is not an issue.

Dave

OK, I think I understand now.
When calibrating a VNA to the standards, an adjustment is made by the software
as to exactly where the reference plane is.

The calibration could have been structured such that we see the three dots
when measuring the calibration standards.
But then the reference plane would not be at a convenient position
for performing measurements.

Jerry, KE7ER

To do a proper cal on most modern VNA or PNA first the kit used it identified to
the machine. The -032kit (SMA) from HP is know the the Agilent E8357 PNA
by the kit number and will correct for any flaws in the actual physical standards
by adding the correction factors already stored. The end result is three dots.

Substitute a different kit and you get a different result without calibrating.
I used kits for N, BNC, SMA, SMB and TNC and also terminated wires
as a part of the nominal work done (antenna measurements).

However whats going on requires understanding transmission lines, and
PNA internal operation. Agilent has a few good presentations on it.

However the NanoVNA is good and simple but nowhere near the level of
accuracy, and dynamic range. Before you get into the load and cal you
have to also recognize the error level and internal math limitations.

In the end its a plane of calibration that has to be understood, not
how long it is to the short (phase distance).

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

On Tue, 18 Aug 2020 at 18:38, Jerry Gaffke via groups.io <jgaffke=
[email protected]> wrote:

Links within the FAQ now work. thanks!

I could understand the results shown in that FAQ

if the VNA is calibrated using one set of O-S-L standards

and the VNA is then used to measure the open and short standard

from some other calibration kit.

But if the VNA is measuring the standards to which it was calibrated,

should it not show the Smith chart at the top of the FAQ, with three nice
clean dots?

Jerry, KE7ER

If, after calibration, there were perfect opens and shorts* at the
reference plane*, there would be dots. But the standards apply opens and
shorts some distance from the reference plane, so the arcs exist.

The delay on that female short is 27.99 ps. The delay on the male short is
significantly longer (63.078 ps), so had I shown the male, the arc would
have been more than twice the length.

Dave


--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

We should clarify something here regarding very short (as a function of
free space wavelength) radiators.

A short radiator (a short monopole or small open ended 'wires' of a
transmission line) exhibits an extremely *low real part *of the feed
impedance or radiation resistance (neglecting ohmic losses, for the time
being). The impedance is predominantly capacitive. It forms a capacitive
probe to free space and is typically a very inefficient radiator due to
resulting small currents whose fields (generated by those moving or
oscillating charge carriers) open onto free space. A large series inductor
is required to 'resonate' with this capacitance which boosts the generated
fields due to increased currents at resonance. Remember, resonance is
defined by the absence of the complex term in the feed or radiation
impedance. Most of the current in such a structure exists below the
inductor (loaded mobile whip) and on the structure to which the loaded
"antenna' is attached. What's left is the radiation resistance and the
ohmic resistance of the coil support and the wire of the inductor, itself.
Typically, the sum of the last two greatly exceeds the radiation resistance
- that which produces the energy radiated into free space - by a good
amount.

Small radiating structures exhibit a low real part and a large complex
(capacitive) portion of the feed impedance.

Dave - W?LEV

On Tue, Aug 18, 2020 at 5:48 PM Jerry Gaffke via groups.io <jgaffke=
[email protected]> wrote:

Jim's response is making some sense, I think.
Ideal transmission lines and antenna wires, and ideal caps and inductors
in a matching network,
they should all be lossless.

The primary issue with very small out-of-tune dipoles is likely in
building an impedance matching network
using real components with resistance and dielectric losses to go from the
50 ohms of a transmitter
to the ridiculously high input impedance of that diminutive dipole.

Though the 50 to 3000 ohm impedance transformation needed for an EFHW can
be efficient enough.

No, I haven't read that book yet.

Jerry, KE7ER



On Sun, Aug 16, 2020 at 06:48 PM, Jerry Gaffke wrote:

Jim wrote:

You would have problems in other senses, some of which manifest in what
you might call efficiency.
The radiation resistance gets very low, so the current, for a given
radiated power, gets very high.
So, for a "real antenna" that has ohmic loss, that becomes a big

fraction

of the "power at the terminals"

A transmission line with an open at the end has zero current and maximum
voltage there.
A very short dipole would be a minor step away from that case,
Seems the impedance into such a short dipole should be very high and the
antenna current thus very low.
Though Jim used the phrase "for a given radiated power", which

complicates

things some.

Guess I better read that book.

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

Thank you Wofgang and Dave for pointing out the obvious I have two Bird type meters and slugs that have been considered to be the standard in commercial radio service for decades. They are rated at 5%. I have several hundred dollars invested and happily use them. I would suggest that you who are designing this product put a tolerance of 5% on it. Then when these discussions get started everyone has a quick answer. I am old enough to understand what “don’t try to make a silk purse out of a sows ear” means. Sorry to you who are designing this. It is hardly a “sows ear.” Actually I find this to be one of the finest products I have seen in years. I already have two and put them to good use. Thank you!

Actually I have enjoyed the discussions. There is a lot to learn here. But, ladies and gentleman, let’s understand that you cannot make these more accurate then what they were intended to be. From what I understand they were intended to be used by amateurs for that purpose. They could also be used for commercial radio for 95% of all applications. That is a great deal for $60! Enjoy. For those of you who work in laboratories I don’t understand where you get the budget to purchase tens (or more likely hundreds) of thousands of dollars worth of equipment. I’m a little jealous.

This reminds me of a joke I heard in the 1960’s. A scientist and an engineer were standing at one end of a gymnasium. At the other end were a couple of beautiful girls. They were told that at the sound of each buzzer they could go on half of the way to them. At the end of three buzzers the scientist was still standing where they started. He was asked what the problem was. He said there was no use because he would never get there. The engineer shouted back that he would get close enough for all practical purposes. I know. Rather sexist, but, I hope you all get the point. This nanoVNA was built for engineers, actually technicians, not scientists.

I will use these primarily for HF and VHF plus 70cm. Mostly I use it for antenna work and maybe lo check out a filter. I might use them for 1296 or 2.4 GHz but rarely. Someday I will figure out how to get them to work on my computer.

Thanks for those who develope the hardware and software.

Joe

Every video on the topic or all of them?
What is wrong with it? As I see it he is just trying to make
his homemade set behave similar to the HP one.
Could you point to a better article/video about
the topic (making your own cal standards).

On Tue, 18 Aug 2020 at 06:59, Dr. David Kirkby, Kirkby Microwave Ltd <
drkirkby@...> wrote:

On Tue, 18 Aug 2020 at 03:06, Dragan Milivojevic <d.milivojevic@...>
wrote:

For flush open etc you might find this interesting:

It is technically flawed in several ways as are several other videos from

the same author. *Every* video I have seen from him are wrong, although
this is is not as bad as others.

It’s not that important that the phase of the open and short are exactly
180 degrees apart. The $11,000 18 GHz Keysight 85050B APC7 calkit is one
example of a kit where no attempt is made to achieve 180 degrees, although
it is technically possible to approach it. I don’t know the figures off
hand, and I can’t be bothered to measure or calculate it, but I would
expect that the phase probably varies from 170 to 180 degrees on the 85050B
yet that kit is very accurate, with an error on the worst standard not
exceeding 0.4 degrees to 8 GHz and 0.6 degrees up to 18 GHz

He makes no attempt to explain why he is aiming to get 180 degrees, other
than to say that his HP kit has 180 degrees. I doubt he has a clue why, as
he never says why.

For waveguide calibration kits you don’t use opens for calibration. Leaving
a waveguide open just makes an antenna with a return loss of about 13 dB.

Instead two shorts of different delays are used. Since wavelength in
waveguide is not inversely proportional to frequency, there’s a massive
difference between the phases in waveguide as the frequency is swept.

2) He has a totally flawed video on reference planes. His misunderstanding
of that can be seen in this video too, but it more subtle.

I find YouTube to be awash with people creating videos about things they
know
a little about. He is one such example.

Dave.
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom