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Wondering if anyone has tried to use the nanoVNA to evaluate the properties of the clamp on ferrite chokes that are employed to reduce radio frequency interference (RFI) being emitted by wall wart switching supplies etc. I am not sure how one would do that...use some kind of standard pair of wires like an AC line or adapter cord and measure S11 (single end attached) or S21 (both ends attached) with and without the ferrite clamped on? A similar question would be how to evaluate a common mode choke made by coiling coax around a cylinder form of some kind.

Coil coax around a ferrite and connect the outer shield for a S21 measurement. Loss in S21 = choking :) typical ferrite for line noise choking is #31 (also for top bands 160m - 80m). #43 does a great all-round job on higher bands. #52 is a newer kid on the block. Higher curie temperature, which translates to higher power rating + it's quite capable on all ham bands. All of this from perspective of an HF ham radio operator ;)

A |S21| measurement is reasonable. However, the signature for a lossy choke should also be apparent in a S11 measurement. So take a short length of #22 AWG enamel wire and tie it across the CH0 port of the VNA. The inductance measured if it is reasonable length of wire, say 100 nH should follow a CW trajectory on the chart, along the 50 ohm circle (blue). When the lossy ferrite material is added, I would expect an increase in L as well increase in series R. The result is an increase CW rotation over the same frequency swept range as well a shift of the circle contour to the right. See figure (red) . Try it, see what you get.

Alan

On Mon, Sep 23, 2019 at 12:18 AM, Jeffrey Vandenbroucke wrote:

Coil coax around a ferrite and connect the outer shield for a S21 measurement.
Loss in S21 = choking :

Just so I understand, would I connect only the outer shield to the center pin of the two ports, leaving the center of the coax floating unconnected?

Bruce,
This link might interest you, . It describes a fixture and procedure for measuring ferrite beads using the DG8SAQ VNWA. I believe over their joint frequency range, measurements between the DG8SAQ and nanoVNA have shown close correlation.

Bruce,
There were a couple of accompanying articles to the previous one that go into further detail.
and

A poor mans test jig for checking if these cheap chinese chokes do anything.
Two SMA female chassis connectors with the ground pins soldered together and a short wire connecting the center pins. The nanoVNA is calibrated with the cables connecting to the SMA connectors and the reference plane is at the end of the CH0 SMA connector.
This impedance seen from CH0 is at 100MHz without the choke 52ohm+90nH but with the choke 190ohm+190nH
It seems these chokes are doing something.

Yes, that's all you need. I ran a similar case with a single strand of #22 AWG with and without the addition of the lossy core material. Although very nice particularly for looking at common mode noise suppression, you don't need the fancy test set outlined in the prior post. A measure of S11 along with S21 will demonstrate the sweet spot or corner frequency where the complex permittivity of the core material has its real part equal to its imaginary part. There will be a distinct increase in transmission and reflection loss. I did my test with perm of 4000. Corner frequency ~ 5 MHz.

Alan

I tried the S21 method. Connected the 2 center pins (CH0 and CH1) to the choke ends (coax shield on both ends). -20dB at the frequency of interest is a decent common mode attenuation. -30dB is good. -40dB is excellent, but is hard to achieve.

73, Mike

Thanks all for the replies with detailed information, and also the links, which provide a treasure of information. It looks like the nanoVNA will be extremely helpful in looking at the snap-on ferrite cores - I bought a whole assortment of them from Amazon last year when I was fighting an RFI issue - trying to prevent ingress of RF from my transmitter into a Tivo DVR that kept rebooting. The cores never seemed to have much of an effect. I have a suspicion that they are not the right material for the low frequencies involved (3.5-14 MHz). .. and back then my only tool was whether they worked or not...very unsatisfying. But now...with the nanoVNA I will get to find out what the ferrite cores can or cannot do - hooray!

Hi Bruce and hwalker
Please visit www.reeve.com and read the next report where I tuned in and contributed. The linked article are the first step to better methods ?
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af hwalker
Sendt: 23. september 2019 14:27
Til: [email protected]
Emne: Re: [nanovna-users] Evaluating clamp on ferrite chokes

Bruce,
This link might interest you, . It describes a fixture and procedure for measuring ferrite beads using the DG8SAQ VNWA. I believe over their joint frequency range, measurements between the DG8SAQ and nanoVNA have shown close correlation.

Thanks for the heads up Kurt. I linked to parts 2 & 3 in a subsequent reply. I found the whole series of articles to be interesting reading and hope to construct a similar Test fixture for sorting my cache of unknown ferrites into different types. It will be interesting to see how the nanoVNA performs in such an application. Noting the results you achieved using the test fixture and DG8SAQ to evaluate Type 43 ferrite cable clamps, if you still have the fixture available how about conducting a similar evaluation using the nanoVNA and letting us know if it is up to the task. With your experience in this subject matter, I'm surprised you haven't chimed in sooner.

Herb

Hi Herb
I did notice you already had mentioned part 2 and 3 "plowing" thru the next messages.
Well I need to have a relatively low profile as I am in the midst of a huge project so only limited time.
I first got my NanoVNA a couple of weeks ago, and it was unpacked for a week until I got a half day to play with it.
Indeed NanoVNA can measure the same data as the VNWA. Actually there is a kind of a part 4 never published as it is only some notes and a spreadsheet and some few articles, as the core material measurement in a closed cylindric chamber facilitates measurements of the material, where I eliminate the inductance of the wire/rod passing thru the core material.
Even Fair Rite does not do that, as they use a short wire thru the core. That we got of information from Fair Rite at the time we wrote the articles, but if that still applies I do not know.
If you are interested send me a mail to kurt@... and I will offline send you what I have. I have a zip file with the relevant material.
And no it will not be published here as I have no time for responding to question for the time being.
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af hwalker
Sendt: 24. september 2019 01:09
Til: [email protected]
Emne: Re: [nanovna-users] Evaluating clamp on ferrite chokes

Thanks for the heads up Kurt. I linked to parts 2 & 3 in a subsequent reply. I found the whole series of articles to be interesting reading and hope to construct a similar Test fixture for sorting my cache of unknown ferrites into different types. It will be interesting to see how the nanoVNA performs in such an application. Noting the results you achieved using the test fixture and DG8SAQ to evaluate Type 43 ferrite cable clamps, if you still have the fixture available how about conducting a similar evaluation using the nanoVNA and letting us know if it is up to the task. With your experience in this subject matter, I'm surprised you haven't chimed in sooner.

Herb

On Mon, Sep 23, 2019 at 05:09 PM, Kurt Poulsen wrote:

@The ( /profile/TheBoss )

Very kind of you to offer Kurt. I was an EMC project manager up until I retired, so I know how pressing deadlines are. I have time now-a-days to follow my whims and will mock up a few test set-ups on my own and see what kind of data I get. I'll use the manufacturer's data as a reference as you did in your study. I already have access to a shielded test fixture used for calibrating rf current probes up to 1 GHz, and will it as a jumping off point. If I get any data that looks promising I post to the group.

Regards, Herb

I have a suspicion that they are not the right material for the low frequencies involved (3.5-14 MHz).

For these frequencies, the key is the number of turns. You need a ring (not a snap-on cylinder), and thread the coax as many times as you can through it. If your application is QRP or RX only, use thin coax (like RG-174).
A single snap-on only helps on VHF. You need a dozen of them to see a difference.

73, Mike AF7KR

On Tue, Sep 24, 2019 at 11:45 AM, vbifyz wrote:

I have a suspicion that they are not the right material for the low

frequencies involved (3.5-14 MHz).
For these frequencies, the key is the number of turns. You need a ring (not a
snap-on cylinder), and thread the coax as many times as you can through it. If
your application is QRP or RX only, use thin coax (like RG-174).
A single snap-on only helps on VHF. You need a dozen of them to see a
difference.

73, Mike AF7KR

Mike,
Thanks for the comment - I think you are absolutely right about that for HF. In my case, the ferrite chokes were mainly tried with the wall wart power cord going into a Tivo DVR, and I tried to loop the line a few times around the ferrite. So for nanoVNA measurements I am thinking of sacrificing a dead wall wart to harvest the DC line cord and using that as a test line to try different amounts of looping and different ferrite cores to see if I can tamp down the RF ingress into the Tivo box with the HF frequencies of interest. Going from memory the reboot was triggered even when the TV line coax was disconnected...so the DC power line is the main suspect...unless the chassis itself is picking up the RF.
Bruce KX4AZ

Bruce,
If you wrap the TiIvo in aluminum foil and the interference problem goes away, then you have a shielding problem and the ferrites won't help. If the aluminum foil doesn't help then you are most likely on the right track, and interference is being conducted into the Tivo via the power-line. If that is the case, try wrapping about 5 turns of the power cord on one side of a split ferrite clamp and another five turns on the other side of the clamp before closing it. A dc power filter might also be a solution if you have one handy.

Herb