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I found my RFIV box but not the cable, so I wired it up and its working. It seems noisy. Just measuring my load references I get about +/- 1db noise. If I use a bridge, I get a ruler flat line. Also, changing references dont change the noise on the RFIV. The noise peaks are still there so its in the cables or RFIV unit. Granted I'm not using the top of on the box as I haven't found it yet. I have some cheap reference loads and when I use them the noise shifts with their readings. I have to play with it more, of course.

Any config errors that can cause the noise to be higher in RFIV mode?

thanks

Jerry

Check that Instrument Mode is set to Reflection and RF I-V; Transmission mode should not be used with RF I-V mode.

Also check that calibration mode is set to Response Calibration.

These settings should be applied automatically when RF I-V mode is selected but they may have been inadvertently changed.

Also check that the two co-axial cables are not transposed; I once did this when I first used the fixture with my VNWA.

As I recall, the results were incorrect but, surprisingly, "in the ballpark", probably due to the awesome power of calibration.

There was a discussion of the RF I-V fixture some years ago on the old N2PK Yahoo group; Bill Carver was having a problem with his, I think.

To assist, I did some measurements of a 5k1 0805 resistor and obtained results as seen in the attachment; Paul opined that this was very good, the kind of result that might be expected.

Kerry VK2TIL.

Hi Kerry,
Impressive!
I don't achieve that level. I tried a 5.1k resistor just now too, the charts are set to 10 ohms per division (same as yours), with 1-60MHz range total. I am using ADC speed:9, and ADC Avg:5.
The blue trace is a single sweep, and the red trace is average of 36 sweeps.
There's a chance it could be improved by changing my power supply (I'm using just an average AC/DC converter 5V barrel-plug output brick (Meanwell GST25B05-P1J<>), and inside the N2PK enclosure I created the 10V rail with an ADM660 switched-capacitor voltage doubler chip. That can't be too wise, I should try swapping it out one day. I might also try with a linear 5V PSU at some point, but nevertheless the results seem acceptable for now, just a few tens of ohms noise at such a high DUT resistance.


[cid:6e197815-ba88-496f-92e2-5f27e245fc02]
[cid:48575797-959d-4f89-9a17-76fe560a4bda]


________________________________
From: [email protected] <[email protected]> on behalf of Kerry via groups.io <planningpower@...>
Sent: 28 January 2024 21:07
To: [email protected] <[email protected]>
Subject: Re: [N2PK-VNA] RFIV vs bridge

Check that Instrument Mode is set to Reflection and RF I-V; Transmission mode should not be used with RF I-V mode.

Also check that calibration mode is set to Response Calibration.

These settings should be applied automatically when RF I-V mode is selected but they may have been inadvertently changed.

Also check that the two co-axial cables are not transposed; I once did this when I first used the fixture with my VNWA.

As I recall, the results were incorrect but, surprisingly, "in the ballpark", probably due to the awesome power of calibration.

There was a discussion of the RF I-V fixture some years ago on the old N2PK Yahoo group; Bill Carver was having a problem with his, I think.

To assist, I did some measurements of a 5k1 0805 resistor and obtained results as seen in the attachment; Paul opined that this was very good, the kind of result that might be expected.

Kerry VK2TIL.

G'day Shabaz.

I did some measurements a few days ago on a 10k metal-film leaded resistor; this topic energised me this morning to process the S11 file.

See attached.

It's clear that the RF I-V fixture does not do well at low frequencies; its function is to provide measurements of low and high impedances.

Mine works from 0.5 - 100 MHz.

I haven't used it for low impedances; I have a project that requires measurements down to milliohms so I might use it there.

When I built my N2PK, I built a separate linear power supply; I'm old-fashioned and I don't feel entirely comfortable with switching supplies, although I admit that they have improved greatly over the years.

Photos of my home-made "wall-wart" :) are attached.

Regards, Kerry VK2TIL.

Hi Kerry,

Very nicely built set-up! The supply internals look great.
I started building the VNA and RF-IV adapter just over 10 years ago, and I was a bit naive.
Knowing what I know now, I too would have gone with a linear supply.
I will modify at some point, and post the results.

It was the largest home-built project I'd attempted at the time (and might still be!). I couldn't have done it without the help from everyone on the N2PK mailer. My father was around then, and even though he didn't know what it was, he loved seeing it being assembled, with the careful coax plumbing inside and all, so the VNA project is a whole nice memory for me.

________________________________
From: [email protected] <[email protected]> on behalf of Kerry via groups.io <planningpower@...>
Sent: 29 January 2024 02:24
To: [email protected] <[email protected]>
Subject: Re: [N2PK-VNA] RFIV vs bridge

G'day Shabaz.

I did some measurements a few days ago on a 10k metal-film leaded resistor; this topic energised me this morning to process the S11 file.

See attached.

It's clear that the RF I-V fixture does not do well at low frequencies; its function is to provide measurements of low and high impedances.

Mine works from 0.5 - 100 MHz.

I haven't used it for low impedances; I have a project that requires measurements down to milliohms so I might use it there.

When I built my N2PK, I built a separate linear power supply; I'm old-fashioned and I don't feel entirely comfortable with switching supplies, although I admit that they have improved greatly over the years.

Photos of my home-made "wall-wart" :) are attached.

Regards, Kerry VK2TIL.

I forgot to label the frequency axis of my chart; see attached.

I should also have said, in relation to the power supply, that there is a 5v linear regulator on the rear panel of the VNA; the 12v and 5v lines are protected by "crowbar" over-voltage circuits; see attached.

Kerry VK2TIL.

I posted recently in the VNWA group about building my N2PK;

/g/VNWA/message/22644

I'd been learning about vector measurements, first with a home-made noise bridge and then with a lucky purchase of a HP8405A vector voltmeter, when I heard about the N2PK; I didn't now what a VNA was but I thought I should get one.

Like you, it was a memorable experience; for you, it's a wonderful way to remember your father.

Although I never met him, I still remember Art Allen who sent me the parts; he was so pleasant and patient with a mug like me, and even sent some more parts when I found that one lot, of resistors I think, was the wrong value.

The N2PK was indeed a unique experience; Jeff AC0C said it well in a recent post;

"... every N2PK that comes into existence should be celebrated. They are increasingly rare beasties".


Kerry VK2TIL.

things are working a little better, or were, up until I swapped the power and
ground rebuilding the cable I can't find. Glad I had a current limited supply
feeding it! Things are less noisy now that the cable it tighter in the socket.

Another question I have is if it is possible to get an average only line? Like
on a scope when you hit average in acquisition. I can do the average
accumulate and put the average line up, but I want something that runs for
like 10 minutes averaging all along the way. I'll keep looking.

Jerry

Some VNAs, eg the VNWA, have a trace-smoothing function.

myVNA does not have this. If you want a nice straight trace, set the vertical axis scale to a high value per division.

I think that an Excel plot of the data can be smoothed with a Trendline; I've never done it, though.

I prefer to show the raw data; as a friend who is a high-level microwaves engineer says, "Smoothing is cheating".

Kerry VK2TIL.

Attached are;

Plot of raw data and

Plot of same data with Trendlines.

My engineer friend would be horrified!

Kerry VK2TIL.

Where did you calibrate the load? What resistance?

The attached photos show the setup and calibration standards.

Note that Load calibration is always 50 ohms; the 200-ohm device is used to check that setup and calibration are OK before beginning a measurement. It is NOT part of the calibration.

If I don't "see" 200 ohms, as per the attachment, for a Reflection setup or 9.54 dB loss for a Transmission setup, I know that something is wrong.

Kerry VK2TIL.

Hi,

You might want to check the smoothing function, just one of the beauties in DG8SAQ's VNWA software.
It also runs with N2PK hardware.

Cheers,
Vladimir

G'day Vladimir.

I mentioned this earlier.

I also have a VNWA but I don't like to smooth traces, I prefer the raw data.

I like to use Dave's myVNA with the N2PK; it's my tribute to Dave.

Kerry VK2TIL.

Ooops, sorry, missed your earlier comment.

73, Vladimir

Easy to do in a long thread; I've done it myself.

Nice to see you posting; this group has been quiet for far too long.

Kerry VK2TIL.

If this helps anyone, here is the construction of my RF-IV probe:





73
AE1S

I have a 1.020K .01% resistor and when I try to measure it with RFIV calibrated with 50ohms
it seems to be all over the place. I have to keep working with it I guess. And I need to find the darn top for the unit.

Could it be a configuration setting?
FWIW these are the settings I used in myVNA (unfortunately it keeps license-locking-up on me, it always thinks my laptop hardware has changed, so I'm struggling to use that.
Maybe photos of the board and setup are needed, to see if anything can be visually spotted.


Coax Connections
??????VNA??? RF-IV Sensor
??????RF OUT????? RF IN
??????PORT 1??? OUT
??????PORT 22???? N/A

VNA Hardware
??????Parameter??? Value
??????Hardware Type????? N2PK VNA
??????Configure the hardware??
??????Transmission ADC?? ADC2
??????Reflection ADC???? ADC1
??????Clock Frequency (MHz)??? 156.25
??????Minimum Frequency? 0.05
??????Maximum Frequency? 60
??????ADC Voltage conv. factor? 1.6463612727
??????Hardware Interface?????? USB
??????Choose CDS/Harmonic Mode?? Harmonic Suppression Mode
??????Harmonic ??? Fundamental
??????Samples????? 4 (CDS)
??????Set RF-IV Configuration? ADC1 is used for V and I
??????Switch setting whilst reading V?????Switch Line 0 goes High
??????Reload Z0 with Calibration Data?????Checked
??????Load DDS during ADC????? Checked
??????Swap Detectors on Reverse Scan??????Checked
??????Power Down DDS when Idle??? Checked
????????????

Instrument Mode
??????Parameter???Value
??????Dual Detector Trans/Refl??????Checked
??????Use RF-IV Mode????Checked
????????????

Calibration
??????Parameter??? Value
??????Use Separate Isolation Avg????Checked
??????5 Term Calibration?????? Checked
????????????

Switches and Attenuators
??????Parameter??? Value
??????Attenuator 0?????Checked

________________________________
From: [email protected] <[email protected]> on behalf of Jerry <jerry@...>
Sent: 29 January 2024 17:30
To: [email protected] <[email protected]>
Subject: Re: [N2PK-VNA] RFIV vs bridge

I have a 1.020K .01% resistor and when I try to measure it with RFIV calibrated with 50ohms
it seems to be all over the place. I have to keep working with it I guess. And I need to find the darn top for the unit.