开云体育

I should also mention, I did all measurements with the RF-IV sensor. It seems to work so well, I didn't use a directional coupler.

Thanks,

Shabaz.


________________________________
From: [email protected] <[email protected]> on behalf of Shabaz Yousaf <shabaz_yousaf@...>
Sent: 01 September 2020 01:34
To: [email protected] <[email protected]>
Subject: Re: [N2PK-VNA] Matching for a Xtal filter

Hi Marc,

Thanks for the information, it's great to hear about the procedures used. I've not used the touchstone format yet, that's something I'm looking forward to. I didn't realize VNWA had a matching tool to solve this.
I guess I just needed to persevere, I spent hours today on it, and finally have something I'm happy with for now.
Basically, after thinking about it last night, I figured I must have missed the matched spot due to too few points or something.
Also, my setup was crude. I re-did it all today, replacing the ferrite toroids with more stable T50-6 iron cores, and removing the trimmer capacitor (which was hard to trim) with fixed ceramic capacitors. Although the online calculators (based on the QMF filter datasheet value of 910 ohm//25 pF) had calculated 71 pF, I found that 100 pF worked better to shift some of the peaks more closer to the center of the Smith chart. Also, I had 23 turns of wire on the T50-6 cores for 2.4 uH, and I found I needed to squeeze them to occupy half of the toroid area, i.e. an inductance slightly higher than the calculated 2.4 uH was needed.

Now the filter result looks like this:

The passband peaks are -2.5 dB which is within spec, although the troughs are a little out of spec, but this was a filter bought from ebay so probably to be expected. The stop-band is only -50 dB, which is not good, but I'm guessing it is due to lack of shield between the input and output of the filter, although I did try to position the toroids far apart. A photograph of the construction is here:


I terminated the filter with 50 ohm and did a S11 measurement. The VSWR is 1.4 at the filter peaks, the graph is here:


The other port is only slightly worse, at VSWR of 1.6, graph here:


I placed a sketch of the design here:


Many thanks,

Shabaz.


________________________________
From: [email protected] <[email protected]> on behalf of Marc olanie <Marc.olanie@...>
Sent: 31 August 2020 09:03
To: [email protected] <[email protected]>
Subject: Re: [N2PK-VNA] Matching for a Xtal filter

Hi Shabaz

I'm a lazzy guy and definitely not a "tech pundit". But when I'm playing with xtal filters, I first run a transmission measure in both direction, store the datas in an S2P touchstone file format with at least 1000 to 2000 measurement points (due to the high Q of these devices)

Then I use the VNWA software, and more particularly it's "matching tool" to simulate the input and output impedance transformer, an eye on the ripple of the amplitude trace, an eye on the C// value.
It's a pure "visual" tuning approach and the final "real life result" is identical to the simulated Z match.


VNWA is fully compatible with the N2PK VNA and could be downloaded from the following url


I indifferently use vnwa and myvna, depending on the abilities and qualities of each software.

Cheers
Marc f6itu

-----Message d'origine-----
De : [email protected] <[email protected]> De la part de Shabaz Yousaf via groups.io
Envoyé : lundi 31 ao?t 2020 05:20
? : [email protected]
Objet : [N2PK-VNA] Matching for a Xtal filter

Hi Everyone,

I hope you're well. Although I have some RF background, I don't do this for a day job, I'm very much a beginner so apologies if I'm asking something basic.

I've never had to match such a filter before, but long story short, I have a 8-pole filter model "QMF 10725" which according to the PDF datasheet<> looks like 910 ohm in parallel with 25 pF.
I wish to match to 50 ohms input and output.

According to calculators, that means that I can use a series capacitor of 72 pF and a parallel inductor of 2.4 uH.
I didn't get good results when I tried it (not sure how precisely I need to trim the capacitance and inductance - I would say I had the inductance and capacitance to within a few percent since I measured them at 10.7 MHz).
With the matching circuit attached to the QMF filter, on a Smith Chart I could not get the 10.7MHz point anywhere near the centre, I was just circling not far from the perimeter!

So, I decided to measure the filter on its own (i.e. without any matching) using the RF-IV sensor, to confirm if it is 910 ohm//25pF or not, and I see Rp and Xp as shown in this screenshot:


I'm fairly confident I'm using the RF-IV sensor and MyVNA correctly (I tested with known resistances to confirm the OSL calibration), so I have confidence in the measurements.

As can be seen, in the filter passband, Rp varies considerably. Xp also varies a lot, in some places inductive, and some capacitive.
How can I match it do you think? Should a series C and parallel L be fine, and if so, what values would you suggest?

The CSV file of the data is here:


The Extended CSV is here:


Many thanks,

Shabaz.

Hi Marc,

Thanks for the information, it's great to hear about the procedures used. I've not used the touchstone format yet, that's something I'm looking forward to. I didn't realize VNWA had a matching tool to solve this.
I guess I just needed to persevere, I spent hours today on it, and finally have something I'm happy with for now.
Basically, after thinking about it last night, I figured I must have missed the matched spot due to too few points or something.
Also, my setup was crude. I re-did it all today, replacing the ferrite toroids with more stable T50-6 iron cores, and removing the trimmer capacitor (which was hard to trim) with fixed ceramic capacitors. Although the online calculators (based on the QMF filter datasheet value of 910 ohm//25 pF) had calculated 71 pF, I found that 100 pF worked better to shift some of the peaks more closer to the center of the Smith chart. Also, I had 23 turns of wire on the T50-6 cores for 2.4 uH, and I found I needed to squeeze them to occupy half of the toroid area, i.e. an inductance slightly higher than the calculated 2.4 uH was needed.

Now the filter result looks like this:

The passband peaks are -2.5 dB which is within spec, although the troughs are a little out of spec, but this was a filter bought from ebay so probably to be expected. The stop-band is only -50 dB, which is not good, but I'm guessing it is due to lack of shield between the input and output of the filter, although I did try to position the toroids far apart. A photograph of the construction is here:


I terminated the filter with 50 ohm and did a S11 measurement. The VSWR is 1.4 at the filter peaks, the graph is here:


The other port is only slightly worse, at VSWR of 1.6, graph here:


I placed a sketch of the design here:


Many thanks,

Shabaz.


________________________________
From: [email protected] <[email protected]> on behalf of Marc olanie <Marc.olanie@...>
Sent: 31 August 2020 09:03
To: [email protected] <[email protected]>
Subject: Re: [N2PK-VNA] Matching for a Xtal filter

Hi Shabaz

I'm a lazzy guy and definitely not a "tech pundit". But when I'm playing with xtal filters, I first run a transmission measure in both direction, store the datas in an S2P touchstone file format with at least 1000 to 2000 measurement points (due to the high Q of these devices)

Then I use the VNWA software, and more particularly it's "matching tool" to simulate the input and output impedance transformer, an eye on the ripple of the amplitude trace, an eye on the C// value.
It's a pure "visual" tuning approach and the final "real life result" is identical to the simulated Z match.


VNWA is fully compatible with the N2PK VNA and could be downloaded from the following url


I indifferently use vnwa and myvna, depending on the abilities and qualities of each software.

Cheers
Marc f6itu

-----Message d'origine-----
De : [email protected] <[email protected]> De la part de Shabaz Yousaf via groups.io
Envoyé : lundi 31 ao?t 2020 05:20
? : [email protected]
Objet : [N2PK-VNA] Matching for a Xtal filter

Hi Everyone,

I hope you're well. Although I have some RF background, I don't do this for a day job, I'm very much a beginner so apologies if I'm asking something basic.

I've never had to match such a filter before, but long story short, I have a 8-pole filter model "QMF 10725" which according to the PDF datasheet<> looks like 910 ohm in parallel with 25 pF.
I wish to match to 50 ohms input and output.

According to calculators, that means that I can use a series capacitor of 72 pF and a parallel inductor of 2.4 uH.
I didn't get good results when I tried it (not sure how precisely I need to trim the capacitance and inductance - I would say I had the inductance and capacitance to within a few percent since I measured them at 10.7 MHz).
With the matching circuit attached to the QMF filter, on a Smith Chart I could not get the 10.7MHz point anywhere near the centre, I was just circling not far from the perimeter!

So, I decided to measure the filter on its own (i.e. without any matching) using the RF-IV sensor, to confirm if it is 910 ohm//25pF or not, and I see Rp and Xp as shown in this screenshot:


I'm fairly confident I'm using the RF-IV sensor and MyVNA correctly (I tested with known resistances to confirm the OSL calibration), so I have confidence in the measurements.

As can be seen, in the filter passband, Rp varies considerably. Xp also varies a lot, in some places inductive, and some capacitive.
How can I match it do you think? Should a series C and parallel L be fine, and if so, what values would you suggest?

The CSV file of the data is here:


The Extended CSV is here:


Many thanks,

Shabaz.

Hi Shabaz

I'm a lazzy guy and definitely not a "tech pundit". But when I'm playing with xtal filters, I first run a transmission measure in both direction, store the datas in an S2P touchstone file format with at least 1000 to 2000 measurement points (due to the high Q of these devices)

Then I use the VNWA software, and more particularly it's "matching tool" to simulate the input and output impedance transformer, an eye on the ripple of the amplitude trace, an eye on the C// value.
It's a pure "visual" tuning approach and the final "real life result" is identical to the simulated Z match.


VNWA is fully compatible with the N2PK VNA and could be downloaded from the following url


I indifferently use vnwa and myvna, depending on the abilities and qualities of each software.

Cheers
Marc f6itu

Hi Everyone,

I hope you're well. Although I have some RF background, I don't do this for a day job, I'm very much a beginner so apologies if I'm asking something basic.

I've never had to match such a filter before, but long story short, I have a 8-pole filter
model "QMF 10725" which according to the PDF datasheet<> looks like 910 ohm in parallel with 25 pF.
I wish to match to 50 ohms input and output.

According to calculators, that means that I can use a series capacitor of 72 pF and a parallel inductor of 2.4 uH.
I didn't get good results when I tried it (not sure how precisely I need to trim the capacitance and inductance - I would say I had the inductance and capacitance to within a few percent since I measured them at 10.7 MHz).
With the matching circuit attached to the QMF filter, on a Smith Chart I could not get the 10.7MHz point anywhere near the centre, I was just circling not far from the perimeter!

So, I decided to measure the filter on its own (i.e. without any matching) using the RF-IV sensor, to confirm if it is 910 ohm//25pF or not, and I see Rp and Xp as shown in this screenshot:


I'm fairly confident I'm using the RF-IV sensor and MyVNA correctly (I tested with known resistances to confirm the OSL calibration), so I have confidence in the measurements.

As can be seen, in the filter passband, Rp varies considerably. Xp also varies a lot, in some places inductive, and some capacitive.
How can I match it do you think? Should a series C and parallel L be fine, and if so, what values would you suggest?

The CSV file of the data is here:


The Extended CSV is here:


Many thanks,

Shabaz.

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

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

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

Greetings

Q can be derived for either L or C by measuring their complex impedance .? In either case Q is a ratio of the real to imaginary values provided by the VNA.? I have recently spent considerable hobby time using my N2PK VNA to derive equivalent series resistance (ESR) of high quality fixed? capacitors.

My bottom line is that accurate measurement becomes increasingly challenging for capacitors with values less than 100 pF and at frequencies below 10MHz or above 100MHz

One academic study bluntly concluded that a? VNA is unsuited to the task and several manufactures use other measurement instruments.

I have a 6-page summary of my efforts, let me know if you would like a copy if anyone

73 Ron W6WO

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

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

Hello folks,
After many years of great service my N2PK VNA has developed a problem, it acts like it's detectors both have poor sensitivity. Can anyone give me some guidance troubleshooting? Drop me a email and I will try to describe the problem a little better and the steps I have taken. Thanks I sure miss this thing!!

Hi

I am wondering whether anyone might have a single detector PCB available. I am looking to update a rather old single detector N2PK VNA to a dual detector for use by a friend.

Thanks.

Bob, 5B4AGN

Thanks Gary.

Unfortunately it shows solid continuity when I test it.

I have replaced the regulator as well - the replacement and the original behaving the same, unfortunately.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

Sounds like the gnd terminal of the regulator is floating. Mine behaved normally.

Gary NA6O

I've finished a v5.2 board and the VNA seems to be operating properly.? However there was one odd observation that I was hoping someone in the group may have seen before, or have a theory about.

The 3.3V regulator that feeds the CW master osc shows 3.3V **without** the CW MO connected.? With the CW MO connected, the 3.3V terminal reads about 3.55V.? Roughly 0.25V high.

Notes:

1. The voltage tracks the 5V rail.? If the 5V rail is set to 5.1V, the observed voltage is higher yet, about 3.6V.

2. The regulator is not oscillating.? I have measured the voltage at the terminal with 2 HP lab DVM, a fluke, an oscilliscope and a SA.? There is some level of the 156 Mhz present on the +3.3V line, but I'm not sure if that's just being picked up by the near proximity of the oscillator's ajacent output.? I've replaced both the 0.1 & 10 uF caps ajacent the CW osc just for good measure.

3. The VNA seems to work fine with as-expected noise floor levels.

4. While the CW part is a 3.3V nominal, the abs max voltage is 5V so even if the circuit is truly running at 3.55V, the oscillator is probably not in mortal peril.

5. Checks of nearby points show nothing in the 3.55V or 0.25V range.

6. With the +3.3V feed from the regulator pulled, the voltages around the CW osc are all zero.

7. The CW oscillator output is clean and stable.? I can see 2nd/3rd harmonic levels but it looks like it's working fine.

8. Current consumption of the oscillator is about 30 mA which I think is in line with the datasheet values.

At the moment I have no explanation for this.? Hoping someone would have a theory.? Or be able to check their board and see if they have a similar observation on the MO voltage.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

Hi all
I have a problem.
I calibrate in reflection mode, then I apply again the load used to calibrate
and display the Xp.
See enclosed the result, glitches ?
Help
IZ2ZNC Gianfranco

Paul,

Thanks for the excellent piece of test equipment. Your groundbreaking work as spawned many designs but your VNA still has tput if piece of quality test equip,emy in the hands of experimenters.

73, Mike N2MS

Hi Paul,

Any estimate of how many N2PK VNA's were constructed over the years?

Steve, K8JQ

Hi All,

Ivan has kindly added an archived copy of my now defunct website to his website here:

<>

I have also updated my QRZ page to reflect this.

Stay safe,
Paul

Hi
I am using the myVNA 1.0.0.95
When I import a any configuration ( transmission, S-Parameters etc )
appears tick also " TDR mode only".
I have to un tick it and everything works properly.
Any explanation ?
Thanks
Regards
IZ2ZNC Gianfranco