开云体育

Dave, out of curiosity I created a circuit model for a common-mode choke. It has an inductance, capacitance, and resistance in parallel. I chose the values to mimic attenuation results for a common-mode choke someone sent me a couple years ago. It's shown below. The choke was measured with a DG8SAQ VNA with all four S-parameters. The software that accompanies the VNA can implement what they call scripts. He ran the Y21 script and sent the results. One of the neat features of the Y21 method is that it can calculate the shunt capacitance at each port as well as the DUT response with the capacitance nulled mathematically. Calculated shunt C was 2.8 to 7.3 pF depending on port and frequency. (I don't know why it varies with frequency.) I used his choke to create my choke model. When I added a shunt 2.7 pF to each side of the choke in the model, I saw no difference in choke attenuation to 30 MHz. I thought at least it would be noticeable, but the curves overlap. I tried 27 pF to make sure the model was working, and I could then see a small difference. 2.7 pF is about 2k ohms at 30 MHz. This is comparable to the usual several-k ohm CMC impedance so I expected some effect. You can notice the Y21/S21 difference below for a shunt capacitance roughly double what you measured. The effect isn't great and is of no consequence for choke attenuation, but it would be measurable.

One thing I often forget is that measured capacitance for a test fixture like yours includes the connector capacitance. It is not stray capacitance. It matches the connector inductance to form a 50 ohm impedance. You should subtract the capacitance of a bare connector from the 2.7 pF you measured to get the stray fixture capacitance. There is also capacitive coupling between the choke and the VNA enclosure if it is nearby. That will contribute to shunt capacitance.

Based on my circuit model. I think the capacitance of your fixture should have a negligible effect at HF. It would be a good idea to verify that expectation by measurement.

Brian

I have found that all beepers can be permanently silenced with a pair of diagonal cutters. ;-)
A less invasive method is to stuff the transducer full with putty, Blue Tac, epoxy or similar physical means.
73, Don N2VGU

On Mon, May 19, 2025 at 03:28 PM, W0LEV wrote:

That certainly is quite low especially for
HF frequencies.

Thanks for the info, Dave. Please measure a common-mode choke using the fixture with your HP VNA with S11, S21, S12, and S22 and post the .s2p. I'll see how the Y21 method compares with the usual S21 method. Any difference will be due to the shunt fixture capacitance.

Brian

1) My take on dynamic range is the ratio between the fixture with nothing
between the two ports to a fat and short as possible conductor between the
ports. With the recent images and using the HP8753C, that measured 80 dB
over the HF frequency range.

2) The capacitance at each port is 2.7 pF measured directly at each BNC
connector. I just measured it. That certainly is quite low especially for
HF frequencies.

Dave - W?LEV

On Mon, May 19, 2025 at 5:04?PM Brian Beezley via groups.io <k6sti=
[email protected]> wrote:

OK, after looking more carefully at the photos, I think you're referring
to the ratio of the desired signal through the device under test to the
residual feedthrough with the device absent. Correct me if I'm wrong.

Did you consider the effect of the increased capacitance to ground at each
port? It looks like it may be substantial. Easy to measure.

Brian

--

*Dave - W?LEV*


--
Dave - W?LEV

And with HP test equipment now KeySight, I dub it KeyOutOfSight.

On Mon, May 19, 2025 at 12:57?PM Clyde Spencer via groups.io <cftr01b=
[email protected]> wrote:

One of the definitions for HP is High Price!!

*Clyde K. Spencer*


On Sun, May 18, 2025, 11:17?PM Charles VK1CM via groups.io
<mrcharlesmuller=
[email protected]> wrote:

I nearly fell out of my chair when I saw the HP fixture prices. May I
suggest using these:



There is a lot of other goodies on his website, and I have found him very
easy to deal with.

Regards,


Charles.
VK1CM

One of the definitions for HP is High Price!!

*Clyde K. Spencer*


On Sun, May 18, 2025, 11:17?PM Charles VK1CM via groups.io <mrcharlesmuller=
[email protected]> wrote:

I nearly fell out of my chair when I saw the HP fixture prices. May I
suggest using these:



There is a lot of other goodies on his website, and I have found him very
easy to deal with.

Regards,


Charles.
VK1CM

OK, after looking more carefully at the photos, I think you're referring to the ratio of the desired signal through the device under test to the residual feedthrough with the device absent. Correct me if I'm wrong.

Did you consider the effect of the increased capacitance to ground at each port? It looks like it may be substantial. Easy to measure.

Brian

On Mon, May 19, 2025 at 09:40 AM, W0LEV wrote:

that old fixture was limited to about 35 dB of dynamic range

Dave, what do you mean by dynamic range in this context?

Brian

You've all seen my fixture I use for evaluating transmission measurements
on various items, especially common mode chokes, filters, and other
circuits.

Well, that old fixture was limited to about 35 dB of dynamic range over the
HF frequencies, nominally 1 through 30 MHz. One day I went to work using
various methods to up that dynamic range. I ended up with easily 75 dB of
range after about 2-hours of work on the older fixture using the HP3585
spectrum analyzer with its tracking generator. Yesterday, I verified that
75 dB of dynamic range using the HP8753C. With that instrument the fixture
measured closer to 80 dB of range over 1 to 30 MHz. Have a look at the
attached images for the physical construction. YMMV.

Dave - W?LEV


--
Dave - W?LEV

Yes. My last visit to JB was just after they closed. Sitting on the
concrete table outside the store was a Tektronix 7623A, with a sign on it
that read "FREE". You can guess what happened next. JB was the local parts
source for common parts for us at Benchmark. As far as I know JB was the
last surplus store (of the four that existed back in the 90s) to close and
I'm guessing that no new ones have opened since.

My sister worked at Sandia and told me about the surplus store there.

And don't forget the StorageTek surplus store. My Simpson 260xi came from
there. It was basically free (maybe $5 or something like that).

DaveD
KC0WJN


On Mon, May 19, 2025 at 11:42 W0LEV via groups.io <davearea51a=
[email protected]> wrote:

Dave, we all miss J. B. !! I can't count the number of times we,
collectively, solved (unpaid consulting) design problem with unknown
designers in the isles of J. B. Saunders. And......, then found the parts
to buy. They are sorely missed ! ! !

And in New Mexico: The surplus sales at both Los Alamos and Sandia.

Dave - W?LEV

On Mon, May 19, 2025 at 3:33?PM Dave Daniel via groups.io <kc0wjn=
[email protected]> wrote:

And J. B. Saunders ....

DaveD
KC0WJN


On Mon, May 19, 2025 at 11:24 AG6CX via groups.io <edwmccann=
[email protected]> wrote:

And Yardley Beers, W0JF, a Boulder legend along with McGukins.

Ed McCann
AG6CX

On May 19, 2025, at 8:21?AM, Dave Daniel via groups.io <kc0wjn=

[email protected]> wrote:

?I severely miss McGuckins.

DaveD

On 5/19/2025 11:03 AM, W0LEV via groups.io wrote:
Any good hardware store may have them. Also a good electrical

supply

house. Likely, the chains will not have such items.

We have an excellent "have everything" and then some hardware store

in

Boulder. They are an independent.

Dave - W?LEV

On Mon, May 19, 2025 at 1:51?AM WB9YXA via groups.io <ahoffman1=
[email protected]> wrote:

Dave,

Where did you find the very large alligator clip shown in the

photos

in

the document? My usual sources aren't turning up anything big

enough

to

bite a bnc connector.

Just curious.

Andy

--
This email has been checked for viruses by Avast antivirus software.
www.avast.com

--

*Dave - W?LEV*


--
Dave - W?LEV

Dave, we all miss J. B. !! I can't count the number of times we,
collectively, solved (unpaid consulting) design problem with unknown
designers in the isles of J. B. Saunders. And......, then found the parts
to buy. They are sorely missed ! ! !

And in New Mexico: The surplus sales at both Los Alamos and Sandia.

Dave - W?LEV

On Mon, May 19, 2025 at 3:33?PM Dave Daniel via groups.io <kc0wjn=
[email protected]> wrote:

And J. B. Saunders ....

DaveD
KC0WJN


On Mon, May 19, 2025 at 11:24 AG6CX via groups.io <edwmccann=
[email protected]> wrote:

And Yardley Beers, W0JF, a Boulder legend along with McGukins.

Ed McCann
AG6CX

On May 19, 2025, at 8:21?AM, Dave Daniel via groups.io <kc0wjn=

[email protected]> wrote:

?I severely miss McGuckins.

DaveD

On 5/19/2025 11:03 AM, W0LEV via groups.io wrote:
Any good hardware store may have them. Also a good electrical supply
house. Likely, the chains will not have such items.

We have an excellent "have everything" and then some hardware store in
Boulder. They are an independent.

Dave - W?LEV

On Mon, May 19, 2025 at 1:51?AM WB9YXA via groups.io <ahoffman1=
[email protected]> wrote:

Dave,

Where did you find the very large alligator clip shown in the photos

in

the document? My usual sources aren't turning up anything big enough

to

bite a bnc connector.

Just curious.

Andy

--
This email has been checked for viruses by Avast antivirus software.
www.avast.com

--

*Dave - W?LEV*


--
Dave - W?LEV

And J. B. Saunders ....

DaveD
KC0WJN


On Mon, May 19, 2025 at 11:24 AG6CX via groups.io <edwmccann=
[email protected]> wrote:

And Yardley Beers, W0JF, a Boulder legend along with McGukins.

Ed McCann
AG6CX

On May 19, 2025, at 8:21?AM, Dave Daniel via groups.io <kc0wjn=

[email protected]> wrote:

?I severely miss McGuckins.

DaveD

On 5/19/2025 11:03 AM, W0LEV via groups.io wrote:
Any good hardware store may have them. Also a good electrical supply
house. Likely, the chains will not have such items.

We have an excellent "have everything" and then some hardware store in
Boulder. They are an independent.

Dave - W?LEV

On Mon, May 19, 2025 at 1:51?AM WB9YXA via groups.io <ahoffman1=
[email protected]> wrote:

Dave,

Where did you find the very large alligator clip shown in the photos in
the document? My usual sources aren't turning up anything big enough

to

bite a bnc connector.

Just curious.

Andy

--
This email has been checked for viruses by Avast antivirus software.
www.avast.com

Yes, when we can't find something at Ace, we head to Boulder. White Rock,
New Mexico also had something similar that "served" the lab at Los Alamos.

Good hardware stores are rare these days with all the chains.

Dave - W?LEV

On Mon, May 19, 2025 at 3:21?PM Dave Daniel via groups.io <kc0wjn=
[email protected]> wrote:

I severely miss McGuckins.

DaveD

On 5/19/2025 11:03 AM, W0LEV via groups.io wrote:

Any good hardware store may have them. Also a good electrical supply
house. Likely, the chains will not have such items.

We have an excellent "have everything" and then some hardware store in
Boulder. They are an independent.

Dave - W?LEV

On Mon, May 19, 2025 at 1:51?AM WB9YXA via groups.io <ahoffman1=
[email protected]> wrote:

Dave,

Where did you find the very large alligator clip shown in the photos in
the document? My usual sources aren't turning up anything big enough to
bite a bnc connector.

Just curious.

Andy

--
This email has been checked for viruses by Avast antivirus software.
www.avast.com

--

*Dave - W?LEV*


--
Dave - W?LEV

And Yardley Beers, W0JF, a Boulder legend along with McGukins.

Ed McCann
AG6CX

I severely miss McGuckins.

DaveD

--
This email has been checked for viruses by Avast antivirus software.
www.avast.com

Deepelec has not updated their firmware in several years and their architecture is not the same as your V3.

Why not open the case and disable the beeper? Put some tape across the output port or cut the PCB track.

Any good hardware store may have them. Also a good electrical supply
house. Likely, the chains will not have such items.

We have an excellent "have everything" and then some hardware store in
Boulder. They are an independent.

Dave - W?LEV

On Mon, May 19, 2025 at 1:51?AM WB9YXA via groups.io <ahoffman1=
[email protected]> wrote:

Dave,

Where did you find the very large alligator clip shown in the photos in
the document? My usual sources aren't turning up anything big enough to
bite a bnc connector.

Just curious.

Andy

--

*Dave - W?LEV*


--
Dave - W?LEV

Nizar,

Yes you need to use Enhanced response option for S21. It was created by DiSlord for these types of measurements.

On Sun, May 18, 2025 at 11:17 PM, Charles VK1CM wrote:

There is a lot of other goodies on his website, and I have found him very
easy to deal with.

Makis is a great guy, I have designed one of his products, a dual log detector board, , into a VSWR protection circuit, for my client, after he assured me of its continued availability. Tons of other great, useful products on his site, highly recommended.
73, Don N2VGU

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