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A phase vs frequency plot helps identify where the middle of the transition is. Sometimes that's easier than trying to find the -3dB points. A classic S curve from +90 to -90 degrees phase, and 0 is the center frequency, and +/- 45 degrees are easy to find.

Thanks for all the details, Alan. My program does have group delay, which is differential phase shift. It does extract Q from S11 or S21 when measuring inductance.

I've changed to displaying SWR circles for SWR = 1.5, 2, and 3 simultaneously. I may add another curve for Q contours of 1, 2, and 3. I would leave calculation and interpolation to the user for now.

Any other suggestions for specialized curves or features?

What chart program are you using?

Brian

The rectangular plot of the one port S data is insufficient to
determine Q. You will need the differential phase shift
of the reflection coefficient as well. Taken together with
the appropriate formula the Q can be determined. The chart
facilitates this and overlays that could be clipped onto
the network analyzer screen were available. Or the glass
was etched on screen. Doing this with the nanovna simply
requires the touchstone file and then import this into
the chart program I displayed. There are a other measurement
types available, S21, for example, where the Q is extracted
directly from the screen. Typically, this is a rectangular plot,
although a chart plot can also be used.

The Q is obtained from the reflection coefficient crossing at
zero degrees, 7.003 MHz divided by the 3 dB down power points
where the sweep crosses the Q=1 contour at 7.022 and 6.974 MHz.

The result is 146.

The common name is "constant Q contour" and the Q=1 is somewhat unique in that
it is a locus of points connecting all cases where R=X.

Other contours are available. The Q=2, 3, etc.... where the R,X ratio is 2,3, etc... and this facilitates
the constructs for matching over a desired band when a load model is imported to the chart.

On Mon, May 12, 2025 at 10:17 AM, Jim Lux wrote:

Your only question is "linear frequency scale or log".

Thanks for reminding me, Jim. I've been meaning to look into log scales, both x and y. Right now everything is linear only.

Brian

OK, I see you calculated Q from the marker frequency values. Interpolation would be easy and would improve accuracy. Maybe I could add interpolated Q calculation to the marker. Looks like I would need two markers per curve. Right now I provide just one for each curve.

Does this Q = 1 curve have a common name? Something analogous to circles of constant SWR being called SWR circles.

Brian

There's lots of different ways to plot the same data, and people develop their approaches based on the ones they're familiar with.
I guess, too, in the "bad old days" when plots were done by hand (or plotter) doing it all with one plot was more convenient.

Today, where you can flip among plots in the blink of an eye, yeah, a gain vs frequency plot would be useful. Your only question is "linear frequency scale or log".

Thanks for the illustration. How did you get Q = 145.8? Why does the rectangular plot needs phase slope added to discern? Is the dip it too broad and shallow? A rectangular phase plot is available. How would you use it?

Alan, if I handed you a device and asked you to find the series-resonant frequency and the bandwidth at that point with a NanoVNA, what would you do? If the VNA was equipped with the feature you're proposing, what would you do differently?

Brian

Here is an illustration... attached.

This is true for some measurements but not all...

Consider a one port measurement, only S11, for a shunt series resonator.

The jig is made using one section of the commercially available NanoVNA test board. Available on eBay, Amazon and from Chinese sellers. You can find discussions about this board on several posts in this group.

Alan, I don't understand what you're suggesting. If I wanted to find center frequency and Q, I'd just look at the rectangular plot, which is available.

Brian

Thank you.

A useful addition to your bag is a constant Q contour. The Q = 1
contour permits resonator unloaded Q to be determined from S11
or S21 data overlaid on the chart. Three dB bandwidth and center
frequency is is quick to view.

Hi Roger

Apologies for resurrecting an old post
I was just wondering if you could provide any details on the S11 / S21 test jig, it looks pretty much ideal for the matching tests I would like to try.
I am guessing that this is something you modified yourself & it's not available off the shelf ?
What are the origins of the base board ?

Thx
Brian

Nizar,
The renormalization makes some assumptions that may not apply to your balun, in particular that S11=S22.
This is often close to true for things like ceramic filters, but is probably not close for your balun.
--John Gord

More Smith chart tricks:



Brian

Hi Dave

as asked here below the attached new measurements with renormalized Z0 coax 78.5 Ohm and 50 Ohm ( first balun Zc= 62 Ohm) , cursor at the same frequency 14.125Mhz .

73's Nizar .

Hi Dave

Thanks
I do not use any external artifact to take S21 Losses measurements with equivalent 78.5 Ohm coax Z0 , i just use the DiSlord Z0 renormalisation option on Display menu, this option take on consideration all computing's needed to acte as a real 78.5 Ohm NanoVNA .

For measuring characteristic impedance of my Balun i use My owne purely experimental methode , no computing nor modeling just measuring the resistor value that focused the Smith diagram on one dote (resistor trimmer termination) and read the renormalized impedance value that make it exactly on the center of the the shart, it's easy methode, reliable and accurate enougth without any computing errors and estimation, only direct experimental measurement , see screenshoot illustration.

73's Nizar

According to the Github page it is the latest "Official" release, Feb 24 2025 . I just d/l it last week.
Don't know about older units. I have a Deepelec V3 and seems to be fine

Instead of reading where the plot intersects, read the numbers at the top
of the screen which is where your cursor is placed. You have:

-0.774 dB loss at 54.6 + j 35.2 ohms equivalent of 64 ohms for the
total impedance
-0 440 dB loss at 80.7 + j 24.8 ohms equivalent of 84 ohms for the
total impedance

The total impedance is derived by calculating the SQRT of the SUM of the
SQUARES.

Note that using the reflection measurement option as illustrated in the
first image, the total loss is 0.5 of the measured value as the RF must
pass twice through the network. The ratios above don't change.

So the loss at nominally 54 ohms real is 0.167 dB greater at 81 ohms real.

Also note that due to the non 50-ohm or non 72-ohm Zo of the transmission
line transformer (common mode choke), the Zo of the choke will transform
either resistance to something else between 50 and 80-ohms.

What you are using for your 50 and 72 ohm non-reactive loads for the load
in your common mode choke - the disc in the first picture?

How did you measure the impedance of our common mode choke? I usually take
two measurements to determine this:

1) Measure the capacitance with the far end of the choke open terminated.
This will give you the capacitance of the windings (pretty close).

2) Measure the inductance with the far end of the choke short terminated.
this will give you the inductance of the windings (pretty close).

Measure both of these using the Smith Chart and the cursor.

Then calculate the characteristic impedance of the transmission line choke
(common mode choke) using the following:

Zo = SQRT [Measured Inductance in Henries / Measured Capacitance in Farads]

NOTE: 1 ?H = 1E-6 H and 1 pF = 1E-12 F

Dave - W?LEV



both the

On Sun, May 11, 2025 at 6:03?PM Team-SIM SIM-Mode via groups.io <sim31_team=
[email protected]> wrote:

Hi All

i tryed to change the balun designe with the same FT140-43 but with 1X12
turns this time , I measure the charateristic impedance of the balun is
around 142 Ohm ( see Smith shart focused on the graph center) , but this
time with 78.5 Ohm renormalized coax impedance it gives the half with 50
Ohm normal coax , huge diffrence around 1db at 30Mhz , in add this new
balun seems have much more losses -2.5 db compared to the first one
-0.2db , why ?? what is not correct with this second balun , see
illustration below .
73's Nizar .

--

*Dave - W?LEV*


--
Dave - W?LEV