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  1. N2PK-VNA
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Problem with measuring Q's of Caps & Inductors

 

Hello All,

I haven't posted in years but I need your help now.

The hardware is a single detector board with Pauls original
coupler board unmodified. The software I'm using is MyVNA
version 1.0.0.54 on an XP machine.

Problem. I think I'm having problem measuring the correct Q
of good Caps and Inductors, I never seem to measure a Q
greater than 200. Vacuum Cap or inductors wound on PVC forms.
Why is that? Is this to be expected with the original coupler board?
Should I be using the wider bandwidth RF-IV sensor PCB for
measuring higher impedance parts?

Thanks for your time,

Dave - wb9own
 

Dave,
It might seem like heresy but I would recommend that you download the software that runs the DG8SAQ VNWA.

/g/VNWA/files/A1%20DG8SAQ//VNWA36.7.9.8.zip It will also control the N2PK VNA and is extremely powerful.?

Then investigate the amazing documents written by Kurt, OZ7OU.? One in particular: How to Measure the Resonant Frequency and Q of an Air Coil might be helpful.?? I don't know whether this will make it through but it's attached.

Wes? N7WS

On Wednesday, July 22, 2020, 9:44:10 AM MST, David Garnier <dsgarnier@...> wrote:

Hello All,

I haven't posted in years but I need your help now.

The hardware is a single detector board with Pauls original
coupler board unmodified.? The software I'm using is MyVNA
version 1.0.0.54 on an XP machine.

Problem.? I think I'm having problem measuring the correct Q
of good Caps and Inductors, I never seem to measure a Q
greater than 200.? Vacuum Cap or inductors wound on PVC forms.
Why is that?? Is this to be expected with the original coupler board??
Should I be using the wider bandwidth RF-IV sensor PCB for
measuring higher impedance parts?

Thanks for your time,

Dave - wb9own

How to measure the resonance frequency and Q of an air coil-rev1.pdf
How to measure the resonance frequency and Q of an air coil-rev1.pdf

 

Some years back I was having trouble measuring Q. The values from my HP 4342 and N2PK were no where near the same. Contacted Paul and he suggested getting a rfiv bridge. Things changed dramatically. Now my readings are very realistic with both units. Hope this helps.

Gary
 

Hi Gary,

Thank you for the reply jogging my memory! I vaguely remember long a thread
and the construction of the RFIV head, I wish I would have paid more attention
and built one. I will contact Ivan for PCB.

I've gotten active on 630 meters and I'm trying to evaluate C's & L's hence the
problem. This N2PK VNA keeps giving and giving, every project is a journey.

I also need to thank Paul N2PK for this fine instrument and giving his time support
over the years. This was done in the finest amateur radio traditions, what a
great Elmer gift project this has been.

73's Dave - wb9own

On Thursday, July 23, 2020, 02:45:57 PM CDT, kb4j_2000 via groups.io <kb4j_2000@...> wrote:

Some years back I was having trouble measuring Q.? The values from my HP 4342 and N2PK were no where near the same.? Contacted Paul and he suggested getting a rfiv bridge.? Things changed dramatically.? Now my readings are very realistic with both units. Hope this helps.

Gary
Ron Skelton
 

Greetings to all, In response, the Agilent Impedance Measurement Handbook illustrates where RF-IV is superior to the reflection method.
Measuring capacitor ESR is especially challenging and a study conducted
by D. Stepins, at the university of Riga Latvia focused on capacitor
parameter measurement accuracy using a VNA. It concluded transmission
measurements were the most accurate and reflection methods should not be
used. www.researchgate.net/publication/269166796...

My N2PK VNA has been used to make many reflection and transmission
measurements of capacitor ESR . The reflection method sometimes produced
absurd results. Agilent illustrates this to explain why some ESR values
were negative.

It seems to me that measuring very low values in the presence of much
larger values comes down to the dynamic range of the instrument ESR is
a case in point

Good health,wealth and happiness to all in the N2PK community Ron W6WO

On 2020-07-23 21:50, David Garnier wrote:

Hi Gary,
Thank you for the reply jogging my memory! I vaguely remember long a thread
and the construction of the RFIV head, I wish I would have paid more attention and built one. I will contact Ivan for PCB.
I've gotten active on 630 meters and I'm trying to evaluate C's & L's hence the problem. This N2PK VNA keeps giving and giving, every project is a journey.
I also need to thank Paul N2PK for this fine instrument and giving his time support over the years. This was done in the finest amateur radio traditions, what a
great Elmer gift project this has been.
73's Dave - wb9own
On Thursday, July 23, 2020, 02:45:57 PM CDT, kb4j_2000 via groups.io <kb4j_2000@...> wrote:
Some years back I was having trouble measuring Q. The values from my HP 4342 and N2PK were no where near the same. Contacted Paul and he suggested getting a rfiv bridge. Things changed dramatically. Now my readings are very realistic with both units. Hope this helps.
Gary

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