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Good evening!

I would very much appreciate recommendations on the best version of the NANOVNA that displays reactance values for the markers on the Smith chart, instead of inductance and capacitance.

Thank you very much!

Tom

Excellent Mike. So that is a Qul of 348. I spilt the difference between 6 and 8 ohms... lets say 7... From the appearance of your coil, that seems
reasonable. The material you wound the unit on has a loss tangent. Any idea what it is? Nice if it were .0005 or better.... Suspect it is not.

On Mon, Jul 3, 2023 at 03:27 PM, alan victor wrote:

If difficulty in finding the paper from EDN and the figures, here is a pdf
abbreviated and a test case circuit screen capture. If you are careful in
fixture construction depending on operating frequency, unloaded Q of 350 or
more is easy to obtain. You really need to take care in any Q measurement to
prevent series R losses from accumulating unless you can accurately de-embed
the "stray" R value(s).

Alan

OK I had a go at this with my NanoVNA and got the attached result, which if I follow your calculation correctly equates to Rq = 8.05 ohms.

Coil64 estimates 5.9 ohms which, given the less than ideal test jig I'm using, is not too far off.

Mike


--
Mike

Return it and get a refund. Then go to R & L Electronics and purchase a genuine one. Problem solved!!! PS... This is the very best advise ANYBODY can give you!!!

Alan

I found the article from your earlier link and will give it a go, thanks.

In the meantime I repeated my measurement with NanoVNA-App calibrated for 6401points and got a slightly lower value of 13.6 ohms at resonance.

--
Mike

On Monday 03 July 2023 08:20:00 am DougVL wrote:

I occasionally see them for sale at hamfests. I have gotten a few that way, but I shouldn't have - I haven't used any yet. Not even the big, (relatively) heavy old U.S. military one.
If you look for one that way, be sure that any that you find still has its set of plug-in coils.

I had the thought to get one some time back, and started looking on ebay. It's amazing how many of these units do NOT have any of the coils with them! I know of one guy who took on one of those and proceeded to try and make his own coils, but I'm not feeling that ambitious these days...

I wonder where all of those coils go?

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin

Mike,

the article is in this file /g/Test-Equipment-Design-Construction/files/Q-factor%20%28Q%20is%20the%20inverse%20of%20dissipation%20factor%20DF%29./Method%20simplifies%20testing%20high-Q%20devices;%20Alan%20Victor,%20EDN%20Feb%202002.pdf. [It's no longer available on the EDN website with the all-important diagrams!]

HTH, 73, happy (or otherwise) measuring,

Robin, G8DQX

If difficulty in finding the paper from EDN and the figures, here is a pdf abbreviated and a test case circuit screen capture. If you are careful in fixture construction depending on operating frequency, unloaded Q of 350 or more is easy to obtain. You really need to take care in any Q measurement to prevent series R losses from accumulating unless you can accurately de-embed the "stray" R value(s).

Alan

I occasionally see them for sale at hamfests. I have gotten a few that way, but I shouldn't have - I haven't used any yet. Not even the big, (relatively) heavy old U.S. military one.
If you look for one that way, be sure that any that you find still has its set of plug-in coils.
--
Doug, K8RFT

I am using nanoVNA-H
The product was purchased on Ali Express, and I thought it was genuine, but it was fake.

First of all, I am a Windows 10-64bit user.

What did you do to solve the problem
1. Install stm32080 driver - Failed to solve
2. firmware upgreade or downgreade - 2 out of 5 bricks (0.9.2 << became a brick, 0.9.3 failed to connect to usb, current version 1.2 but failed to connect to usb)
3. Cypress usb installation - failed
4. FTDI usb installation - failed

Is there any way to connect the fake product to the pc? Tried on win7, linux, and macos, but failed.

Unfortunately, if it's not genuine, can't it be connected to the pc?

i want help

On Mon, Jul 3, 2023 at 12:23 AM, alan victor wrote:

Hi Mike,

Please see message # 23812. This documents one approach.

Alan

Thanks Alan I'll have a look at that.
--
Mike

Mike
15 ohms is not too far from what a long inductor made with small gauge wire could have. Q of about 143.
Pete

Mike, Scratch that idea about the scales because it doesn't work the same at 4 MHz where the Z should be about +j503 ohms.

Mike
Is the scale of your reactance graph supposed to be in kohms and not just ohms? I think so because at 3 MHz the impedance of the series L-C would be about -j911 ohms. Correct?
Pete

Hi Mike,

Please see message # 23812. This documents one approach.

Alan

What happens when you try to calibrate it? "Can't get it calibrated" isn't very specific. Does the unit fail to respond correctly at some point in the calibration procedure?

Hi Pete, it's an air cored coil with an inductance of around 108uH. I made the measurement with an 18pF COG capacitor in series so the plot is showing the resistance around the resonant frequency of the circuit. However at 15 ohms it's higher than I was expecting.

--
Mike

For HF and higher frequencies, L >> R and C >> G are generally good assumptions. We can then simplify the general expressions for complex characteristic impedance and complex propagation constant to:

Zo = sqrt(L / C) ohms

gamma = j * omega * sqrt(L * C) radians per unit length

Because the power dissipating elements R and G are assumed to be zero, the real part of gamma, the attention constant, is zero. Note that if we increase L, we increase the number of radians of wavelength that occupy each unit of length. We can therefore delay propagation by increasing L and that has been done with coax by using a spiral center conductor.

Voice frequency telephone cables pairs are often inductively loaded by placing load coils at intervals. The most popular scheme in the Bell System was 88 mH every 6000 feet, but there are other schemes. The velocity of propagation is pretty low for such loaded cables, although the reasons for loading are to reduce the attenuation and make it relatively constant below a cutoff frequency.

I don't know anything in particular about the special cables for tunnels. I would assume that the "leaked" energy would show up as an increase in attenuation, but maybe someone here knows more about those lines.

73,

Maynard
W6PAP

Hi MIke
What component type are you using for the test? Trying to understand why the R is changing myself. I would think the resistance of a fixed series resistor would remain fairly constant if it has low reactance itself. PA3A's article shows an example of measuring the Q of an inductor so it is understandable that he would measure a Q of over 200 and a low resistance for the iron powder Micrometals core. His R stays flat as would be expected. I am not familiar with the 4C65.
Vector network analyzers were not the preferred instrument to us for measuring the Q of a coil. The R is so small with respect to the reactance that small variations of the phase angle and magnitudes of the reflection coefficient would make the Q and the calculated R to vary considerably. The old Q meters remained in favor for many years because they used a parallel tuned circuit method (old Boonton Radio Corp 160 and the HP 4342 for instance). In any case it would be interesting to know what type of inductor you are testing. What is the core?
73, Pete

Doug, I have seen this demo and observed that the calibration procedure was i.m.o. not properly done.
At marker 3:48 of the video you see that after the CAL button in the menu was pressed next the Calibrate button was pressed without pressing RESET first. From the start of this video you may see that memory c0 was already used.
At marker 4:36 of the video the Isolaton and Thru buttons were selected. They are not needed for a one port calibration.
Now at marker 5:01 of the video something remarkable. After the calibration load was removed a swr of 1.37 was showed in the display. With an open port this value should be infinite (theoretically).

Kees

Op 2-7-2023 om 06:06 schreef Doug: