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NanoVNA Saver 0.2.2-1 TDR curves values

 

Hello,

Very pleased to be accepted in this group.
My dumb 1st question: What is the 2 curves values i get when doing a TDR ?
Coaxial length is correctly displayed (i'm very satisfied with the accuracy) but i'm not clear
with the 2 curves definitions.

Thank you for your help.

Best 73,
Rudi, HB9ARI
 

Hi Rudi,
Welcome to the forum!
Please use the WIKI and FILES sections - they contain a lot of good technical and practical information.
Use the search function as well on forum messages - search the hashtags.
There are a couple of printable manuals in the FILES section and links to several in the WIKI.
The user guide that I edit has a section on TDR and shows examples.
Refer to the links at the bottom of any forum email you receive.
Cheers,larry

On Sunday, May 10, 2020, 7:49:55 a.m. GMT-4, Rudolf Schaffer <rudolf.schaffer@...> wrote:

Hello,

Very pleased to be accepted in this group.
My dumb 1st question: What is the 2 curves values i get when doing a TDR ?
Coaxial length is correctly displayed (i'm very satisfied with the accuracy) but i'm not clear
with the 2 curves definitions.

Thank you for your help.

Best 73,
Rudi, HB9ARI
 

Hi Larry,

Thank you for your kind message.

I will use these information to find an answer to

this 1st question and future too !

Best regards,

Rudi

Le 10.05.2020 ¨¤ 16:33, Larry Rothman a ¨¦crit?:
Hi Rudi,
Welcome to the forum!
Please use the WIKI and FILES sections - they contain a lot of good technical and practical information.
Use the search function as well on forum messages - search the hashtags.
There are a couple of printable manuals in the FILES section and links to several in the WIKI.
The user guide that I edit has a section on TDR and shows examples.
Refer to the links at the bottom of any forum email you receive.
Cheers,larry

On Sunday, May 10, 2020, 7:49:55 a.m. GMT-4, Rudolf Schaffer <rudolf.schaffer@...> wrote:
Hello,

Very pleased to be accepted in this group.
My dumb 1st question: What is the 2 curves values i get when doing a TDR ?
Coaxial length is correctly displayed (i'm very satisfied with the accuracy) but i'm not clear
with the 2 curves definitions.

Thank you for your help.

Best 73,
Rudi, HB9ARI
 

Rudi,
NanoSaver uses FFT methods to compute what would happen if you sent an impulse (sharp voltage spike) down the attached line. One trace represents the computed reflection of that impulse from irregularities on the line, like poor connections or changes if line impedance (say, 50 ohms to 75 ohms). The other trace attempts to show the impedance of the line as a function of distance. Unfortunately, the impedance trace does not quite work properly yet: it always shows increasing impedance. A 50 ohm line follwed by a 75 ohm line will show the expected step up in impedance, but a 75 ohm line followed by a 50 ohm line does not show a step down, instead it shows a step up. The developers are working on correcting this.
The firmware on the NanoVNA itself does this correctly. See my message 12494 on how to set up the NanoVNA to show the reflection of a step wave into the cable and read out the impedance along the line.

--John Gord

On Sun, May 10, 2020 at 04:49 AM, Rudolf Schaffer wrote:


Hello,

Very pleased to be accepted in this group.
My dumb 1st question: What is the 2 curves values i get when doing a TDR ?
Coaxial length is correctly displayed (i'm very satisfied with the accuracy)
but i'm not clear
with the 2 curves definitions.

Thank you for your help.

Best 73,
Rudi, HB9ARI
 

Hi John,

Thank you very much for your message and explanations.

It was effectively the impedance curve who was not clear for me; with your help,

it's more clear now !

I will look today for your message 12494, many TNX in advance.

Best regards,

Rudi

Le 10.05.2020 ¨¤ 20:46, John Gord via groups.io a ¨¦crit?:
Rudi,
NanoSaver uses FFT methods to compute what would happen if you sent an impulse (sharp voltage spike) down the attached line. One trace represents the computed reflection of that impulse from irregularities on the line, like poor connections or changes if line impedance (say, 50 ohms to 75 ohms). The other trace attempts to show the impedance of the line as a function of distance. Unfortunately, the impedance trace does not quite work properly yet: it always shows increasing impedance. A 50 ohm line follwed by a 75 ohm line will show the expected step up in impedance, but a 75 ohm line followed by a 50 ohm line does not show a step down, instead it shows a step up. The developers are working on correcting this.
The firmware on the NanoVNA itself does this correctly. See my message 12494 on how to set up the NanoVNA to show the reflection of a step wave into the cable and read out the impedance along the line.

--John Gord

On Sun, May 10, 2020 at 04:49 AM, Rudolf Schaffer wrote:

Hello,

Very pleased to be accepted in this group.
My dumb 1st question: What is the 2 curves values i get when doing a TDR ?
Coaxial length is correctly displayed (i'm very satisfied with the accuracy)
but i'm not clear
with the 2 curves definitions.

Thank you for your help.

Best 73,
Rudi, HB9ARI

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