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I think need recalibrate.
Calibration must remove all errors.

On 6/14/22 4:29 AM, Brian Beezley wrote:

15070000 -1.000470519 -0.000045675
15194750 -1.000452399 -0.000081647
15319500 -1.000464559 -0.000072501
15444250 -1.000433683 -0.000034980
15569000 -1.000416160 -0.000060047
15693750 -1.000486493 -0.000025182
15818500 -1.000452280 -0.000066847
Jim, that's a data sample for the short. The real part is consistently beyond -1.0004. The open is similarly beyond +1. The largest |S11| I found in other .s1p files was 1.0037. I think it is some sort of systematic issue, not noise. Most users will never notice it since the effect is so tiny. My application is sensitive to errors at extreme S11 values, which yield nonphysical results (negative conductivity).

I forgot to mention that the VNA firmware for the open and short was DiSlord 1.2.

Brian

Interesting - I wonder if it's a "round off" or truncation error of some sort.? The "detector" mixes with I/Q 5 kHz, summing, and there could be a 1/2 LSB bias or something like that.

here's the raw I/Q calculation code:

void dsp_process(int16_t *capture, size_t length)

{

uint32_t *p = (uint32_t*)capture;

uint32_t len = length / 2;

uint32_t i;

int32_t samp_s = 0;

int32_t samp_c = 0;

int32_t ref_s = 0;

int32_t ref_c = 0;

for (i = 0; i < len; i++) {

uint32_t sr = *p++;

int16_t ref = sr & 0xffff;

int16_t smp = (sr>>16) & 0xffff;

int32_t s = sincos_tbl[i][0];

int32_t c = sincos_tbl[i][1];

samp_s += smp * s / 16;

samp_c += smp * c / 16;

ref_s += ref * s / 16;

ref_c += ref * c / 16;

}

acc_samp_s = samp_s;

acc_samp_c = samp_c;

acc_ref_s = ref_s;

acc_ref_c = ref_c;

}

raw (uncalibrated) gamma is calculated here

void calculate_gamma(float gamma[2])

{

#if 1

// calculate reflection coeff. by samp divide by ref

float rs = acc_ref_s;

float rc = acc_ref_c;

float rr = rs * rs + rc * rc;

//rr = sqrtf(rr) * 1e8;

float ss = acc_samp_s;

float sc = acc_samp_c;

gamma[0] =(sc * rc + ss * rs) / rr;

gamma[1] =(ss * rc - sc * rs) / rr;

#elif 0

gamma[0] =acc_samp_s;

gamma[1] =acc_samp_c;

#else

gamma[0] =acc_ref_s;

gamma[1] =acc_ref_c;

#endif

}



this is the code that applies the calibration:

if (cal_status & CALSTAT_APPLY)

apply_error_term_at(i);

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;

Carsten, my experience is all antennas, even those off the shelf one, need some finetuning.

1. Tuning - I would recommend the minimal height for tuning purposes is 3-4m over the ground at the end of the antenna and 1.5-2m at the transformer side.
The higher side could be done such you simply put a stone at the end of the parachute cord, and throw it over the tree - you may then move the end of the antenna up and down easily by pulling the stone.
The tuning of the 40/20/15/10m band is easier, as the "tuning sensitivity" there is lower (do not cut off more than 5cm of wire at once), the 80m piece of wire after the 110uH coil is extremely sensitive though - like 5kHz/cm, and, most important information - the Bandwitdh of the 80m band portion with that specific antenna is pretty narrow - like 40-50kHz, this is what you have to decide upfront - where you want to place that 80m segment (it is from 3500-3800kHz and you will place yourself into a 40-50kHz wide segment of it). That is caused by the resonant LC behavior of the 110uH coil and the aprox 2m long wire (acting as the parasitic Capacitor)..
The antenna de-tunes itself a little bit when pulled into higher height after the tuning, how much - it depends on many factors, however.
The transformer - its mounting is also important - as the output of the transformer (where you connect the antenna wire) is extremely sensitive to parasitic capacitancies, it should be at least 20cm off any other parts, especially metal ones.

2. The shape: the "V" horizontal shape will not hurt the swr too much, afaik, but the radiation pattern diagram (which is difficult to plan either - as it depends heavily on the band and the surrounding objects).

I tried this just last week. It seems work like a spectrum analyzer but having doubts about calibration. For this purpose I used Satsagen software and my HackRF One.
--
ALVARO, EA8ARX

15070000 -1.000470519 -0.000045675
15194750 -1.000452399 -0.000081647
15319500 -1.000464559 -0.000072501
15444250 -1.000433683 -0.000034980
15569000 -1.000416160 -0.000060047
15693750 -1.000486493 -0.000025182
15818500 -1.000452280 -0.000066847

Jim, that's a data sample for the short. The real part is consistently beyond -1.0004. The open is similarly beyond +1. The largest |S11| I found in other .s1p files was 1.0037. I think it is some sort of systematic issue, not noise. Most users will never notice it since the effect is so tiny. My application is sensitive to errors at extreme S11 values, which yield nonphysical results (negative conductivity).

I forgot to mention that the VNA firmware for the open and short was DiSlord 1.2.

Brian

@igor-m
The summerhouse is in Sweden (900m2 Lot) , near Halmstad (outskirt of city).
There can be both thunder & high winds (30m/s, when ugly)

I was thinking of hammering 2 x 3M groundrods down , and use 6mm stranded copper for the ground to "my room".
I would love a link to some available proven lightning arrestors, as most seem to be undeliverable.

The EFHW i would like is excactly a 20+3m w 110uH coil.
I was reading that a Common Mode 1:1 ballun should be installed on the feed coax , Lambda 0.05 from the antenna (4.2m for 80m)

Then the 4.2m Coax would act as a counterpoise , and the 1:1 block CM to the schack.

My guess is that i can get the EFHW up 5..6 meter up in the feed end , and maybe 3..4m in the other , my Trees set the limit.
Seller says the 10..40m is tuned in , but the 80M needs to be.

Next time i'm there i'll have to do some measuring w. a 20m measure band , to see what is possible.

Q's :

1:
It would be MEGA impractical for me to tune it , at the final height (i'm not young anymore) , and the tree climbing should be kept to a minimum.
Can i tune it at ie. 2m height , and then mount it at the final place ?

I have bought 90m Parashute Cord , and expect if possible for the branches to make some kind of pulley system at the trees.
But i have to get up to mount these pulleys ... And still let the tree grow.
Was thinking about "Bicycle tube" around the trees , and then some kind of "loop wire " with an isolator in the loop , going through the bicycle tube ring.
At the other end i might need to use a counter weight or ??? , to let the trees sway in the wind.

Total beginner here ....

2:
In order to utilize the 23m length , i might have to make use of 3 trees in a kind of horizontal V - (My Wife is mumbling already) , and a 10m Alu mast at the end of the terrace to get a straight line , would not make it better.


Thank you @all , for your tips and hints

Carsten

@Carsten: Lightning and Static: in the EFHW antenna with the transformer the antenna wire itself is grounded through the secondary and the coax via primary windings (a short for static). Your system has to be grounded somehow, of course (a difficult topic itself). The "Static" means your wire has been slowly charged with quite high voltage due to some atmospheric events - like nearby storm, snow, strong wind, etc. Btw I observed that by myself couple of weeks back - the 22m long wire alone (15m up over the ground, wire not connected to the transformer) charged itself every 5-8sec up to aprox 15kV (I got about 5-6mm long sparks against the grounded balcony handrail every 5-8 seconds) due to a storm ~30km off my QTH.
A direct stroke by lightning is a different story - I doubt you can avoid total damages with direct hit into the antenna, here complete disconnection of the antenna system before incoming storm is the only help, imho. There is a lot of info on the lightning and static protection for antennas, rather difficult topic, sometimes you would need an inspection by an authority whether your antenna system is compliant or not (it depends where you live)..

On 6/13/22 1:31 PM, Brian Beezley wrote:

I've been analyzing Touchstone files Rudy Severns, N6LF, has recorded with his NanoVNA-H4. The magnitude of S11 is greater than 1 for many files. For example, after calibration right at the VNA connector, |S11| was 1.0007 maximum for the open cal part itself. For the short the maximum was 1.0005. For both, |S11| > 1 for all 401 points from 0.1 to 50 MHz.

The images show calculated permittivity and conductivity for a ground probe with the rods in air. The image with most of the points missing used uncorrected data. The other image is for normalized data where |S11| = 1 maximum.

Although normalization solves the problem for my software, I'm curious why |S11| is ever > 1.

Brian

Measurement uncertainty? You're essentially measuring (V refl)/(V incident) with a noisy sensor.?? 1 part per 1000 (1.001) is 60dB.. the SNR of the measurement is in that ballpark.

Calibration peculiarities - you determine the cal coefficients with noisy measurements, so the combination of cal coefficient high, and measurement high,.

The ADC measuring the output of the mixer has an ideal SNR of ~90 dB.? It's a 16 bit adc, so there's some quantization uncertainty. Then there's the arithmetic aspect. The basic software multiplies the ADC numbers by sin and cos, then sums to get I/Q.?? That's done with 16 bit signed integers, 32 bit products, but then truncated before integrating.

There's also the single precision floating point calculation of the various calibration coefficients using single precision float (32 bit, with 24 bit mantissa/significand).

@Carsten: welcome to the club..
EFHW antennas: I built several and I've been helping local OMs with building and measurements. The first step is to acquire an off the shelf one or to build DIY the EFHW antenna. Before the tuning the antenna has to be completely assembled inclusive transformer in a suitable box, coax, connectors, etc.
The next step is to "tune" the antenna - that is the very moment the nanovna comes handy.
An EFHW for 80-10m with 110uH coil for 80m band will fit inside your garden, as it is aprox 22m long system.
The antenna uses a ~110uH coil after the first 40/20/15/10m segment (aprox 20m long), then another aprox 2m length of wire for the 80m band.
You first tune 40-10m band by changing the length of the first aprox 20m wire, then the 80m band by changing the length of the 2m piece of wire.
You always cut the lengths longer than required (the swr minima below the required frequencies) at the beginning, and then you slowly cut off small pieces of wire while you watch the minimum of the SWR on your nanovna on each band such it fits your bands as best as possible.
All you need is to connect S11 of your nanovna to the antenna coax and watch the SWR at the bands frequencies.
There is a lot of guides on the web available how to make a good EFHW antenna!
A great learning exercise for a beginner, indeed!

there were NEVER any v2plus4 clones.. so you will get a genuine one

(i would now maybe buy a lite vna that goes up to over 6ghz but is a similar design as the vna v2 or v2plus4)

the nanovna v2 has an "open source circuit!" ... and the v2plus4 is similar ... only difference is the balun (the plus 4 has a resistive bridge ass far as i know)

but the overall circuit is the same in all of the v2 so ... differences is the directional coupler

greetz sigi dg9bfc


Am 13.06.2022 um 16:16 schrieb Carsten F (OZ1FTG) via groups.io:

I've been analyzing Touchstone files Rudy Severns, N6LF, has recorded with his NanoVNA-H4. The magnitude of S11 is greater than 1 for many files. For example, after calibration right at the VNA connector, |S11| was 1.0007 maximum for the open cal part itself. For the short the maximum was 1.0005. For both, |S11| > 1 for all 401 points from 0.1 to 50 MHz.

The images show calculated permittivity and conductivity for a ground probe with the rods in air. The image with most of the points missing used uncorrected data. The other image is for normalized data where |S11| = 1 maximum.

Although normalization solves the problem for my software, I'm curious why |S11| is ever > 1.

Brian

@All
Thank you for the valuable input.

@Roger , for the nice links to schematic & More specific groups.

@gfmucci for the "Static warning"

@Jim & Zack for the "Don't connect the FT-991A directly to the VNA" :-)
Ps: Jim i finally got a HP 5065A ... :-)

@Dave For that "invaluable tip, about the coax , and the finger/screwdriver" .. I didn't think about this one.

Rgds
Carsten

And as far as static goes:

Remember that any coax is, by design, low loss and can store a sizable
amount of energy as a cylindrical capacitor. So, I always make a practice
of "shorting" any coax I connect to test equipment by firmly placing my
(somewhat damp) finger over the end of the coax before connecting to
anything. After a good lightning storm, you can get quite an "awakening"
with this practice, but it saves expensive and sensitive test equipment.

Dave - W?LEV

On Mon, Jun 13, 2022 at 6:06 PM gfmucci via groups.io <gfmucci=
[email protected]> wrote:

"What is the most likely way that beginners kill their VNA ?"

Static buildup especially in dry climates. I had one DOA and the vendor
said static buildup killed it.

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


--
Dave - W?LEV

I have been really careful about estimating power out of an amp. I have an
HP 435B power meter with an 8484A head. Maximum power to the head is
supposed to be 10 microwatts (-20 dBm). I carefully calculate the
attenuation needed to keep the input to the head within this range. If I
estimate a power amp could be putting out 10 watts, I'll use 70 dB of
attenuation.

Same for the NanoVNA. I have used it to adjust VHF preamps that could
possibly put out +20 dBm with a gain of 20 dB. So I'll put 30 dB of
attenuation on the input. So far I haven't burned out either the HP power
meter or the NanoVNA.

Zack W9SZ

On 6/13/22 11:06 AM, gfmucci via groups.io wrote:

"What is the most likely way that beginners kill their VNA ?"

Static buildup especially in dry climates. I had one DOA and the vendor said static buildup killed it.

The second most likely is "transmitting into it", or, more properly, making S21 measurements on a small amplifier that has output power bigger than the VNA can take. That 20dB gain block, driven with -10 to 0 dBm puts out +10 to +20, which is more than the VNA can take.

"What is the most likely way that beginners kill their VNA ?"

Static buildup especially in dry climates. I had one DOA and the vendor said static buildup killed it.

Carsten,

Here is a link to the manufacturers Web site for your NanoVNA 2 Plus 4 Firmware, instruction manuals and PC software available there.



There are two groups dedicated to your VNA model and you will get more specific help there.
/g/NanoVNAV2/topics
/g/NanoVNA-V2/topics

Roger

Hello Goup

Old Ham here , but have never played with DIY antennas before , and have never had a HF Station.

I have just gotten my first HF Ham station (FT-991A) , as i have "some" room in the summerhouse garden for maybe a 20..25 meter wire.
Now i want to start playing with "Wire antennas" on 3..50MHz bands, more specifically an EHFW to begin with , as a Dipole layout does not really fit.

I have bought on Aliexpress: 1 x "Original NanoVNA V2 Plus4 4 inch 4GHz":

Expect it to arrive within a month or so.
Since it's Ali .. I hope i get a "Real Original" , not a "CN reduced Clone" .. Lets see.

Any URL to a Schematic of the above VNA ??


When i get it , i see 3 steps to begin with (Focus on antenna measurements) :

1: What firmware to load on the VNA (An URL would be nice)

2: What PC program to use if i want to "Pull out data" (An URL would be nice)
I would prefer Linux (Ubuntu/Mint) , but i have Win10 also if that enhances the experience for a beginner.

3: How to get started with antenna measurements - the tough part i guess .....
When i see a Smith Chart , I always think it's either a "Childs drawing" or a "Vortex from StarTreck".

I just got the Absolute_Beginner_Guide_NanoVNA_v1_6.pdf from the files section , and also some relevant smith chart info from there.

But a "Quick guide, if it exists" just to get started would be invaluable.

Ohh ... A Do & DON'T guide would be nice too :-)
I'd expect for starters , to just feed the Antenna from the VNA, when measuring with the VNA.
What is the most likely way that beginners kill their VNA ?


TIA
Carsten F

Yes, the TinySA is a far better tool for your proposed application.

However, the NANOVNA can be used to measure the isolation between two
antennas. Use it in a 2-terminal transmission measurement setup. One
antenna connects to port zero and the other antenna connects to port one.
You will be able to directly measure the isolation between the two
antennas.

Dave - W?LEV

--
Dave - W?LEV