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On 2/16/22 6:16 AM, Alan Brown via groups.io wrote:

I’m no wiser after these posts.
S21 does not work as not able to calibrate it.
It has gone bad. Overload.
Is there a fix? I’m measuring gain of a LNA as I have done many times and now the port is bad.
I don’t remember breaking it but I probably did as just takes a few seconds not thinking.
I was about to order a new H4 and this one will work for things I don’t need S21 port for.
What is it I’d have to change is the VNA, resistor chip etc??

This is a H4? Original NanoVNA RF design, just with a bigger screen? The first thing after the CH1 input is a resistive pad (I can't remember how many dB, but something like 17-20 dB). I would have thought that's pretty robust against a momentary overload. How much did your LNA put into it? The next thing in the chain is the mixer, but that should be able to handle 0dBm without damage and probably more - it's a bipolar Gilbert cell, and the inputs drive the bases of an NPN transistor.? This isn't some delicate CMOS or MOSFET. So, did you put more than ~100mW in?? Or worse yet, hook it up to the supply voltage without a DC block (e.g. if your LNA expects a bias T or something like that) - 12V across the 56 ohm input resistor is ~200mA or 2.5W - That teeny, tiny SMT resistor won't handle that.? After that goes open, the 12V is then across the 240 ohm series resistors and ultimately the SA612 input

You could probably measure the resistors in the pad to see if one or more is cooked.

OTOH, if it's a NanoVNA2, I believe they have an RF switch as the first thing after the connector, and those are fairly sensitive to overload.

I’m no wiser after these posts.
S21 does not work as not able to calibrate it.
It has gone bad. Overload.
Is there a fix? I’m measuring gain of a LNA as I have done many times and now the port is bad.
I don’t remember breaking it but I probably did as just takes a few seconds not thinking.
I was about to order a new H4 and this one will work for things I don’t need S21 port for.
What is it I’d have to change is the VNA, resistor chip etc??

Has anyone wound a high common mode impedance 1:1 balun with 50 ohm coax and calibrate at the output end of the balun?

I made a balun years ago for use with GR Z bridges (GR 1606 and 916) for this purpose with good results.

I didn't wind the coax on a ferrite toroid at the time. I wound the coax on a length of PVC pipe and with a variable cap across the coax (shield to shield) I tuned it to resonance for the frequency of the test. The common mode Z is very high and higher than a ferrite-cored balun.

Obviously this would not work for a swept frequency test but should work with a broadband ferrite-cored balun.

What I wanted to say here is:

A quarterwavelength at 500 kHz = 150m electrical.
A 1/4 wave physical cable with VF=0.78 would then be 150 x 0.78 = 117m long or with a VF of 0,66:? 150 x 0.66 = 99m
So sweeping from 500 kHz up will be sufficient for coax upto 100m long or so.
For longer cables one has to start with a lower frequency.

Arie


Op 12-2-2022 om 01:47 schreef Bob Ecclestone:

I've measured windowline many times using the NANO - something I can not
easily accomplish with the HP 8753C. Be sure the NANO is not connected to
any conducting cabling, chargers, USB cables, or sitting on or near
anything conducting. At HF frequencies the NANO is small enough to not
influence measurements. However, if it is connected to anything
conducting, it is no longer "small" as a function of frequency /
wavelength.

The attachment indicates you have connected the NANO to a PC. The NANO
effectively becomes much larger at RF frequencies as its connected to: 1)
the USB cable, 2) the PC, and 3) the house wiring, and finally, 4) the
power grid. This will greatly influence correct readings of windowline.
Measurements must be made with the NANO alone.

Dave - W?LEV



On Tue, Feb 15, 2022 at 4:40 PM Kevin Zembower via groups.io <kevin=
[email protected]> wrote:

I'm wondering if the correct way to measure the length of window line
with a NanoVNA is fundamentally different than that of measuring coax.

I'm following the method described by Arie
(/g/nanovna-users/message/26832). I have 5.175m of "JSC
1320 300 Ohm Ladder Line 300 Ohm 20 AWG / 7 Strands Bare Copper". That's
a quarter wavelength of 20.7m, or a frequency of 14.5MHz.

The first step is to sweep it to determine the velocity factor. Yet,
when I sweep from 12-17MHz, I get the Smith chart attached. There's no
point when the impedance is close to zero.

Am I doing something wrong (most probable), or is measuring the length
of window line with an NanoVNA fundamentally different than measuring coax?

Thanks for your advice and suggestions.

-Kevin
KC3KZ

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

I'm wondering if the correct way to measure the length of window line
with a NanoVNA is fundamentally different than that of measuring coax.

I'm following the method described by Arie
(/g/nanovna-users/message/26832). I have 5.175m of "JSC
1320 300 Ohm Ladder Line 300 Ohm 20 AWG / 7 Strands Bare Copper". That's
a quarter wavelength of 20.7m, or a frequency of 14.5MHz.

The first step is to sweep it to determine the velocity factor. Yet,
when I sweep from 12-17MHz, I get the Smith chart attached. There's no
point when the impedance is close to zero.

Am I doing something wrong (most probable), or is measuring the length
of window line with an NanoVNA fundamentally different than measuring coax?

Thanks for your advice and suggestions.

-Kevin
KC3KZ

Hi , some time ,is it necessary to force the installation of the STM drivers as wrote on readme.txt , inside the directory of the
en.stsw-stm32102.

/ (C) COPYRIGHT 2018 STMicroelectronics
* File Name : readme.txt
* Author : MCD Application Team
* Version : V1.5.0
* Date : 02/05/2018
* Description : read me file for Virtual COM Port driver

* THE PRESENT SOFTWARE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS
* WITH CODING INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME.
* AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT,
* INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE
* CONTENT OF SUCH SOFTWARE AND/OR THE USE MADE BY CUSTOMERS OF THE CODING
* INFORMATION CONTAINED HEREIN IN CONNECTION WITH THEIR PRODUCTS.
****/

Last version

- V1.5.0 - 02/05/2018
Supported OS


+ Windows 98SE, 2000, XP, Vista, Seven, 8.x (x86 & x64 Windows platforms)

Contents
*
+ VCP_V1.5.0_Setup_W7_x86_32bits.exe : Setup file to Copy required files for Win7 x86
+ VCP_V1.5.0_Setup_W7_x64_64bits.exe : Setup file to Copy required files for Win7 x64
+ VCP_V1.5.0_Setup_W8_x86_32bits.exe : Setup file to Copy required files for Win8 x86
+ VCP_V1.5.0_Setup_W8_x64_64bits.exe : Setup file to Copy required files for Win8 x64
+ version.txt : History of versions
+ readme.txt : This file

How to use


1- Uninstall previous versions (Start-> Settings-> Control Panel-> Add or remove programs)

2- Run your "VCP_V1.5.0_Setup_W7_x86_32bits.exe" or "VCP_V1.5.0_Setup_W7_x64_64bits.exe" or "VCP_V1.5.0_Setup_W8_x86_32bits.exe" or "VCP_V1.5.0_Setup_W8_x64_64bits.exe" depending on your machine OS

if you like to force the driver install , any time after the first install :

3- Go to Your installation directory - Example, C:\Program Files (x86)\STMicroelectronics\Software\Virtual comport driver

4- Go to Your OS version directory ([Win7] or [Win8])
+ Then :
- Double click on dpinst_x86.exe if you are running a 32-bits OS version
- Double click on dpinst_amd64.exe if you are running a 64-bits OS version
+ Follow the instructions.



**** (C) COPYRIGHT 2018 STMicroelectronics END OF FILE*
Maurizio

This solution solved my issue, which was exactly the same as OP. Thank you sir!!

Tim NC0Q

David,
The SD card routines have been tweaked to work with most TF cards in SPI mode.
Unfortunately, not all cards support that mode of operation.
Most newer cards do support SPI mode.

I could not find any of my SanDisk 16gb cards that would work.
Switched to a Samsung 32gb and it worked perfectly.

On 2/13/22 11:27 PM, Maurizio IZ1MDJ wrote:

Hi , in my opinion , calibrate the S11 port , with 20 dB of attenuation applied , make non sense .
Maurizio

Yes, I'd put the 20 dB pad on the UUT output (i.e. the CH1 port, not the CH0 port).? Then you do a calibration (with the pad in place).? Measure your UUT, add 20 dB to the S21 magnitude. You could also measure the pad separately (with a conventional SOT calibration), measure the UUT and pad, then do the arithmetic.

I think Jim was saying two things:

1) Calibrate it normally and then measure a known device, like e a 20dB attenuator, and see if you get a sane result.

2) If measuring a (say) 20dB amplifier, put 20dB of attenuation after it, so you don’t overload the input.

73, Willie N1JBJ

Hi , in my opinion , calibrate the S11 port , with 20 dB of attenuation applied , make non sense .
Maurizio

On 2/13/22 3:37 PM, Alan Brown via groups.io wrote:

Trying to use log mag and not working now.
I think I overload S21 with more then 10db.
What is the fix anyone now?
I’m hoping some simple right at the port

If you check with a thru and/or a pad, do you get the right values (i.e. did you not damage anything).


You can put 20 dB attenuation at the output of your amplifier under test. Calibrate (Short, open, thru) using the pad.

Trying to use log mag and not working now.
I think I overload S21 with more then 10db.
What is the fix anyone now?
I’m hoping some simple right at the port

For information only:
Ham-Con this year will be both in-person and online. It is scheduled on Feb, 26th, 2022. Before Feb 20th, entrance is $6, after it is $10. See all the information on
Thanks
Bob, k1bif

Did anyone read my initial reply to this thread? All this was there, but
not using the TDR.

Dave - W?LEV

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

This one is very easy to answer as a cable engineer having used both TDR
and OTDR Test Equipment in the past.
All you do is get an exact known length of cable, attach it to your TDR,
dial in a vp UNTIL you get the exact length on the instrument.
That is the vp by virtue of test and measurement.
OR
Follow this guide:



On Sun, Feb 6, 2022 at 11:33 PM lobos305 via groups.io <lobos305=
[email protected]> wrote:

What velocity factor would you use to measure the physical length of a
cable when you don't know the cable type?

Pat

--

Tim Cash | Senior RF/Optical Systems Engineer

cash.tim@...

Hi Bob,

What I wrote about the 150m is not a calculation of a cable length. I was showing that the electrical length is 200m for a physical length of 150m. :-)

About the quality of the nanoVNA H3.2 that I have: you have to be careful. There's no temperature compensation for example. But on the other hand, I was able to measure resistance <0.5 ohm with good accuracy in the HF range and I also tested the nano on 10kohms. Spot on. But I needed some calculus to get there.

In several articles I have explained how to measure those kind of impedances with the nano. The ways to do that are well known in the professional world, but not to hamradio guys/galls of which I am one ;-)


Arie


Op 12-2-2022 om 01:47 schreef Bob Ecclestone:

On Tue, Feb 8, 2022 at 02:16 AM, Arie Kleingeld PA3A wrote:

As an example:
- the measured frequency = 11.7 MHz
- a full wavelength for this frequency = 300 / 11.7 = 25,64m
- a quarter of this is: 25,64 / 4 = 6,41m
So the electrical length of the 5m line = 6,41m and physical length = 5m
Therefore the VF = 5 / 6,41 = 0.78


Now measure the unknown length of transmissionline the same way to find
the frequency where the line is a quarter wavelength long.
Sweep S11 starting at a low frequency for example 500 kHz for a long
transmissionline ** to find the quarterwave frequency. Calculate the
quarter wavelenght in meters; divide it by the VF that you found above
and then you will know the length of the line.

(** A quarter wavelength at 500 kHz is 600m / 4 = 150m and taking into
account the VF, the electrical length will be 150/0,78 = nearly 200m,
should be enough :-)? )

Boy, the guys at CERN should have bought a NanoVNA and used some fancy math instead of building the Large Hadron Collider!
That way they could achieve 1.28C for 10's of Euros instead of Billions! (Calculated Cable Length 200 / Electrical length 150 = 1.28)
Sorry Arie, easy enough mistake to make.

I joined the group a short while ago and am very impressed by the wealth of knowledge and advice out there. So thanks to all contributors.
When I saw this post, I was sure someone would reply straight away, but nobody did. I am only doing so to help those who are new to Amateur Radio and/or transmission line theory.

The method for determining the Velocity Factor (VF) in the example above is correct. (And very well explained)

For the newbies amongst us, you will find if you MULTIPLY the Electrical Length by the Velocity Factor *(VF) you will get the correct Cable Length.
RF slows down as it travels along a cable compared to its speed in free space, about 300,000,000Kms/sec or 300m per microsecond.
In the example Arie gives, The Cable Length would be 150 * 0.78 = 117m (not ~200m). Hopefully enough :-)

Cheers...Bob VK2ZRE