Re: nanoVNA-H net com usb port
I have check Core Isolation and it is OFF.
Many thanks. There are other driver that not permit activation of this protection.
Thank you for help.
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73 de Salvo IZ7VLL.
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Re: Variation in readings of R value
Thanks Alan, and thanks to everyone else for sharing your knowledge and experience.
But now I must move on. The sun is shining and the coil is up in the air. I have optimised the antenna wire lengths for resonance and I'm looking forward to making some good contacts.
I have another similar coil and will continue the measurements on that when I get a moment.
Mike
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Mike
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Re: nanoVNA-H net com usb port
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Re: nanoVNA-H net com usb port
I have the same problem. Now I'm waiting for new one.
I able to upgrade firmware but not to use vna with app on Windows 10 or Debian 12.
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73 de Salvo IZ7VLL.
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Re: Variation in readings of R value
I should add, strap a bar or plate where the LC is located to get a sense of the fixture R. Back out that mesured loss to get Rs fixture. You
can use that mesure to provide some correction.
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Re: Variation in readings of R value
In the same fixture, check the inserted 15 ohm only. The uniform loss should be ~ 8.5 dB.
It is possible that not all the current with the LC inserted is passing via the inserted R.
Since this is a distributed loss,
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Re: Variation in readings of R value
Hi Brian,
Thank you for your explanations.
That is what I love about this forum, I learn something every day.
The coil length explanation is really interesting and makes sense given your explanation.
As for the resistance issue, I felt a niggle as I wrote it. I would have put it down to skin effect. But I was not aware of the proximity effect. Makes sense.
Again thanks for the excellent explanations.
Cheers...Bob VK2ZRE
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Show quoted text
On 6/07/2023 10:12 pm, Brian Beezley wrote: On Wed, Jul 5, 2023 at 09:26 PM, Bob Ecclestone VK2ZRE wrote:
But in your 2nd iteration, I notice the coil length is significantly longer
(156.8mm vs 80mm) with the same coil diameter (37.5mm) yet the inductance
remains the same at 97.8uH.
Surely the inductance should increase. Bob, for a given number of turns, inductance decreases as the coil is lengthened due to lower coupling between turns. The optimizer maximizes Q while keeping inductance constant. It increased the number of turns just enough to compensate for the smaller coupling in the longer coil.
And finally, the Resistance (of the winding?) for the 2nd iteration is lower
than the 1st despite using a longer length of wire (6 vs 7.39).
Resistance is the RF resistance of the coil plus leads due to all causes. It is R in the R + jX model. Mike close-wound his coil with no space between turns. This minimizes coil length but maximizes the proximity effect. This magnetic effect bunches current inside a turn due to the proximity of adjacent turns. It increases RF resistance in the same way as the skin effect, by reducing available copper. The proximity effect is strong. I've never seen a close-wound coil where spacing the turns didn't increase Q even if it required more wire. The optimizer increases coil length to the point where any additional drop in the proximity effect is offset by the increase in wire resistance.
Brian
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Re: Variation in readings of R value
On Wed, Jul 5, 2023 at 09:26 PM, Bob Ecclestone VK2ZRE wrote:
But in your 2nd iteration, I notice the coil length is significantly longer
(156.8mm vs 80mm) with the same coil diameter (37.5mm) yet the inductance
remains the same at 97.8uH.
Surely the inductance should increase.
Bob, for a given number of turns, inductance decreases as the coil is lengthened due to lower coupling between turns. The optimizer maximizes Q while keeping inductance constant. It increased the number of turns just enough to compensate for the smaller coupling in the longer coil.
And finally, the Resistance (of the winding?) for the 2nd iteration is lower
than the 1st despite using a longer length of wire (6 vs 7.39).
Resistance is the RF resistance of the coil plus leads due to all causes. It is R in the R + jX model. Mike close-wound his coil with no space between turns. This minimizes coil length but maximizes the proximity effect. This magnetic effect bunches current inside a turn due to the proximity of adjacent turns. It increases RF resistance in the same way as the skin effect, by reducing available copper. The proximity effect is strong. I've never seen a close-wound coil where spacing the turns didn't increase Q even if it required more wire. The optimizer increases coil length to the point where any additional drop in the proximity effect is offset by the increase in wire resistance. Brian
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Re: Variation in readings of R value
On Wed, Jul 5, 2023 at 02:55 PM, Mike wrote:
It's solid, not foam.
Actually foam, being mostly air, would be better. Another approach would be to drill many holes in the material, leaving a skeletal frame which, again, is mostly air. This is essentially what B&W does with their Miniductor stock, plastic rods are melted into the wire coils, stabilizing them physically while ensuring that the electric fields mostly encounter air. 73, Don N2VGU
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Re: Variation in readings of R value
On Wed, Jul 5, 2023 at 08:30 PM, alan victor wrote:
Hi Mike.
I suspect that the dielectric loss of your coil is secondary. A Qul of nearly
350 implies to me that the primary losses are likely copper wire R and
fixture.
A couple of useful things to do. Place a known R in series with the coil.
Deliberate de-Q and return to a measurement on Rs.
The number calculated should make sense. Example, suspect 7 ohms is the "real"
number, place a 10 ohm (low inductance R) not a WW, you should
see say 17 ohms. This is simply a sanity check.
Second, in looking at your solenoid coil, the L/D ratio looks wrong for
optimum Q. Something like L/D of 0.5 to 1 per Terman is better served for Q.
There is quite a few papers on this relation. But worth investigating if Q is
the big deal.
Hi Alan I tried the experiment with a 15 ohm carbon resistor but it didn't produce the expected result. The calculated resistance went up from 7.5 ohm to 12.6 ohm. I'm aware of the effect of L/D on Q. On a previous antenna I used a coil diameter of 48mm but I want to reduce the visual impact because our garden backs on to a footpath around a lake. -- Mike
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Re: Variation in readings of R value
Hi Brian,
I do not pretend to be any sort of expert here, so I have probably missed something vital.
But in your 2nd iteration, I notice the coil length is significantly longer (156.8mm vs 80mm) with the same coil diameter (37.5mm) yet the inductance remains the same at 97.8uH.
Surely the inductance should increase.
Even if the coil windings were spaced in the 2nd iteration, the Wire Length indicates just more turns as do the Turns (105 vs 79).
And finally, the Resistance (of the winding?) for the 2nd iteration is lower than the 1st despite using a longer length of wire (6 vs 7.39).
Just wondering...
Cheers...Bob VK2ZRE
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Show quoted text
On 6/07/2023 6:30 am, Brian Beezley wrote: On Wed, Jul 5, 2023 at 12:30 PM, alan victor wrote:
Second, in looking at your solenoid coil, the L/D ratio looks wrong for
optimum Q. Something like L/D of 0.5 to 1 per Terman is better served for Q.
Rules of thumb are handy, but today it's easy to directly optimize a coil design. The first image show's Mike's coil. The second shows it after optimizing turns and coil length. The third is after optimizing turns, coil length, and coil diameter. Q could be further improved by using thicker wire. The optimizer uses the Differential Evolution algorithm.
I suspect that the dielectric loss of your coil is secondary.
Form loss shows the loss in the coil form as a percentage of total loss.
The coil program is here:
Brian
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Re: Variation in readings of R value
All,
What about radiation from the coil? Another basic definition for Q relates to the energy stored / energy lost. If energy is lost to radiation that needs to be considered as well.
Very interesting about the PVC. Thanks for that and other aspects of Q. This discussion makes me want to go back and tinker with this stuff but not now when I can still paddle my kayak:)
73, Pete
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Re: Best NANOVNA Version that displays reactance, not uH & C
Thank you Roger!
Yep, looks like mine's older than that. Sounds like a firmware update will get me fixed up. That menu map is WAY more extensive than what I have. Looking forward to it!
Thanks again!
Tom AE5I
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Re: Best NANOVNA Version that displays reactance, not uH & C
On Wed, Jul 5, 2023 at 02:10 PM, Tom AE5I wrote: Thanks very much! I had looked for that and didn't find it, but I'll look
again. Mine's pretty early. Might have been added between the time mine was
made and yours?
The option was added to the firmware around January 2021. If yours is old update the firmware. Lots of nice features and bug fixes over the years.
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Re: Best NANOVNA Version that displays reactance, not uH & C
Well, I see the Polar/Rect menu options, but I don't see anything about the nature of the reactance display. Mine must be from before they added that.
What hardware and firmware do you have? (No rush, just when convenient to check on it). And would you recommend it?
Thanks again!
Tom AE5I
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Re: Variation in readings of R value
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Re: Best NANOVNA Version that displays reactance, not uH & C
Hi Roger-
Thanks very much! I had looked for that and didn't find it, but I'll look again. Mine's pretty early. Might have been added between the time mine was made and yours?
Thanks again... Back to searching the menus!
73 de Tom AE5I
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Re: Variation in readings of R value
On Wed, Jul 5, 2023 at 12:30 PM, alan victor wrote:
Second, in looking at your solenoid coil, the L/D ratio looks wrong for
optimum Q. Something like L/D of 0.5 to 1 per Terman is better served for Q.
Rules of thumb are handy, but today it's easy to directly optimize a coil design. The first image show's Mike's coil. The second shows it after optimizing turns and coil length. The third is after optimizing turns, coil length, and coil diameter. Q could be further improved by using thicker wire. The optimizer uses the Differential Evolution algorithm.
I suspect that the dielectric loss of your coil is secondary.
Form loss shows the loss in the coil form as a percentage of total loss. The coil program is here: Brian
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Re: Variation in readings of R value
Hi Mike.
I suspect that the dielectric loss of your coil is secondary. A Qul of nearly 350 implies to me that the primary losses are likely copper wire R and fixture.
A couple of useful things to do. Place a known R in series with the coil. Deliberate de-Q and return to a measurement on Rs.
The number calculated should make sense. Example, suspect 7 ohms is the "real" number, place a 10 ohm (low inductance R) not a WW, you should
see say 17 ohms. This is simply a sanity check.
Second, in looking at your solenoid coil, the L/D ratio looks wrong for optimum Q. Something like L/D of 0.5 to 1 per Terman is better served for Q.
There is quite a few papers on this relation. But worth investigating if Q is the big deal.
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Re: Variation in readings of R value
On Wed, Jul 5, 2023 at 05:57 PM, Jim Lux wrote:
On 7/5/23 7:58 AM, Mike wrote:
After all that debate about PVC I've just discovered that my coil former is actually ABS ...
Apologies!
Ohh. Black ABS? As in Drain Waste Vent (DWV) pipe?
The black is from carbon black as a pigment - yeah, as in resistors
Also, most DWV is what is known as "cellular" which means that the walls
are actually foamed ABS, with smooth ABS skin on them. Makes it nice and
lightweight, since it doesn't have to hold pressure.
Some is lossy, some isn't.
No I wouldn't use black for that reason. It's white (see photo further up this thread). It's solid, not foam. -- Mike
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Donald S Brant Jr
Roger Need
