Re: Pickup Coil Construction for Inductor Measuremenfs
On Fri, Jun 30, 2023 at 01:28 PM, Bob AF9W wrote:
need to measure some inductors
The nano can measure inductance all by itself, too. Or, at least give you the impedance at the frequency you are measuring with. And the recent -H firmware versions have a specific "find resonance" function/feature/menu choice as well. But, as mentioned above, the connections between nano and coil will limit the absolute accuracy of the reading. Some users build special connection jigs for particular measurements. Connecting your trap directly to the nano may give you the info you need too. You can see the shape of the curve as well as get numerical values. -- Doug, K8RFT
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Thank you very much for your explanations.
1/ We found in old spectrum analyzers for RADAR (1960) delay lines made of a coaxial cable with losses. Our teacher had told us that it allowed to have a lower speed of propagation. I guess we can say that it is a lossy coaxial therefore presenting a complex characteristic impedance (true or false?). If we use a nanaoVNA, what will be the consequences?
2/ More recently I have seen the use of radiating coaxial cable to retransmit radios in the tunnels. This is a cable where the outer conductor is split. This type of cable also has a complex characteristic impedance. Also, what would be the consequence with a nanoVNA?
--
F1AMM
Fran?ois
De la part de Maynard Wright, P. E., W6PAP
Envoy¨¦ : vendredi 30 juin 2023 20:23
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Re: Pickup Coil Construction for Inductor Measuremenfs
On 6/30/23 2:07 PM, Leif M wrote: I hope this is not a silly question, but where do you need GDO, if you have a VNA? That is, you can measure coils and capacitors with VNA. Measuring resonance frequency is bit harder, because Q gets easily too low, and it depends on firmware how you can find the resonance.
It's hard to measure an assembled trap (or measure self resonance of a coil) with traditional 1 or 2 port fixtures, because the fixture is part of the system. I suppose you could develop some appropriate calibration loads (equiv to Short, Open, Load) to "dembed" the fixture. But if what you're interested is resonant frequency, then a "loosely coupled" coil hooked to the VNA to measure S11 works pretty well. The loose coupling reduces the loading from the measurement system, and you can support the unit under test well away from other "stuff". We've used a similar technique at JPL to measure the resonance and Q of a microwave cavity at cryogenic temperatures. You can fill the cavity with, say, liquid methane, or ethane, or mixtures of them, and measure the EM properties. The cavity has two loop probes and we make multiple measurements as the probe orientation changes, and from that can calculate the effect of the probe. (Why? Because oceans on Titan are likely liquid methane, ethane, etc)
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Re: Pickup Coil Construction for Inductor Measuremenfs
Thanks,, Mike.
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On Fri, Jun 30, 2023 at 11:35 AM, Mike wrote:
Hi Bob
If you look at /g/nanovna-users/message/33324 you will see a
picture of a pickup coil I made. It's 5 turns of 0.9mm enamelled copper wire
on a 20mm diameter PVC former. This worked well at around 20MHz.
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Bob AF9W
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Re: Pickup Coil Construction for Inductor Measuremenfs
I am measuring traps in a bandpass filter in circuit for tuning the filter. I have created some pickup coils that "sort of" work but I am looking for an improved solution. I'm using the Nanovna to find the resonant frequency of the traps in a Cauer filter.
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Bob AF9W
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Re: Outliers in group delay measurement
Can you measure just the area where the spike is. I have had odd readings when the scale has been too coarse, and have missed some retails..
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Equivalent circuit=Spice model is not same as impedance. VNA gives you impedance, Coil64 and give you equivalent circuit. Or an approximation of it.
.
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Re: Pickup Coil Construction for Inductor Measuremenfs
I hope this is not a silly question, but where do you need GDO, if you have a VNA? That is, you can measure coils and capacitors with VNA. Measuring resonance frequency is bit harder, because Q gets easily too low, and it depends on firmware how you can find the resonance.
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Re: Pickup Coil Construction for Inductor Measuremenfs
On Fri, Jun 30, 2023 at 06:28 PM, Bob AF9W wrote:
There have been references to pickup coils to use the Nanovna as a GDO. Since
I have zero experience with a GDO and have a need to measure some inductors,
could someone provide some specifics on constructing the pickup coil (or
coils)? What size wire for the coil? How many turns? Is the coil connected
from the center pin to the shield of the connector?
Thanks.
--
Bob AF9W
Hi Bob If you look at /g/nanovna-users/message/33324 you will see a picture of a pickup coil I made. It's 5 turns of 0.9mm enamelled copper wire on a 20mm diameter PVC former. This worked well at around 20MHz. -- Mike G8GYW
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Telecommunications engineers who work with transmission lines (telephone cable pairs) that exhibit complex characteristic impedances (Zo) generally use return loss and reflection loss to characterize those facilities, not SWR and reflection coefficient.
The reason might best be made clear by an example from voice frequency transmission where the angle of Zo is close to -45 degrees. An ideal case might be a cable pair that presents Zo = 600 - j600 ohms at 1000 Hz. To transmit maximum power to the load, we should make the load (Zl) the conjugate of the line, 600 + j600 ohms.
Then the reflection coefficient = rho = (Zl - Zo) / (Zl + Zo) = 0 - j1 ohms
SWR = (1 + |rho|) / (1 - |rho|) = infinity
If you use the replacement theorem I mentioned previously to replace a portion of the load's impedance with an equivalent voltage generator, you will find that it generates a voltage that is in quadrature with the current and satisifies the calculation of the reflection coefficient. An examination of the voltage waveform as a function of position along the line away from the load will show that the voltages are periodically out of phase and add vectorially to zero as is required by the denominator of the SWR expression.
So both the reflection coefficient and the SWR are calculated correctly for such an extreme case, but they are not meaningful as measures of performance as are return loss and reflection loss. If you deal with Zo complex, but with a smaller imaginary component, just be aware that for Zo other than real, the reflection coefficient and SWR will not be exact measures of what is happening in the line.
Chipman points out that, from an exact standpoint, SWR has meaning only for a losless line. When the line is lossy, adjacent peaks and nulls in voltage will not be measured (or calculated) from the same signal voltages and their ratios will not be a mathematically accurate measure of the performance of the line. We can ignore this in most practical cases. He points out that we often assume that Zo = sqrt(L / C) and, for the same line, assume some loss, which means that either R or G or both cannot be zero. The small errors caused by these assumptions can usually be ignored.
73,
Maynard
W6PAP
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On 6/28/23 08:37, Maynard Wright, P. E., W6PAP wrote: Everitt and Anner, "Communication Engineering," Third Edition, McGraw-Hill, 1956, provide a general method (pages 330-331) for examining a mismatch between a source and load, such as a transmission line feeding an antenna.? They factor the source and the load into series networks, one element of which in each case is Zo, the desired impedance.
They then use "Compensation Theorem A" from page 107, which states":
"Any impedance in a network (either linear or nonlinear) may be replaced by a generator of zero internal impedance, whose generated voltage at every instant is equal to the instantaneous potential difference produced across the replaced impedance by the current flowing through it."
Using this theorem, they replace the added network segments by voltage generators so that the resultant equivalent network consists of a matched source and load with added voltage generators to represent the voltages generated by the mismatch.
I applied this to the special case of the complex conjugate load in "More Octave for Complex Zo," QEX, September/October, 2019.? In that case, no modification of the source voltage or impedance is needed and the complex conjugate load is replaced by a matched load (image impedance) in series with a reactance of opposite sign that is twice the value of the reactance of the complex conjugate load's reactance.? That "extra" reactance may then be replaced by a complex voltage source of zero internal impedance that will be seen to be generating a voltage that corresponds to the value of the reflected signal.
73,
Maynard
W6PAP
On 6/26/23 23:01, Fran?ois wrote:
That's it, we have converged. In my application where I am looking for an equality between a value obtained by scanning and a target value, the distance between between the two points (in the complex plane) is a much better criterion for a good result than the ROS which only complicates by creating a non-monotonic function.
When the result of the calculation is equal to the target, the ROS is indeed ONE and the distance zero. It is in the search for the optimal that the ROS disrupts everything.
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Pickup Coil Construction for Inductor Measuremenfs
There have been references to pickup coils to use the Nanovna as a GDO. Since I have zero experience with a GDO and have a need to measure some inductors, could someone provide some specifics on constructing the pickup coil (or coils)? What size wire for the coil? How many turns? Is the coil connected from the center pin to the shield of the connector?
Thanks.
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Bob AF9W
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Re: Connecting NanoVNA, antenna, and manual tuner
Using a smith chart VNA with a manual antenna will be an eye opening experience. You will never want to go back to the hunt and peck method of the three controls.
Lester B Veenstra K1YCM M?YCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)
lester@...
452 Stable Ln
Keyser WV 26726 USA
GPS: 39.336826 N 78.982287 W (Google)
GPS: 39.33682 N 78.9823741 W (GPSDO)
Telephones:
Home: +1-304-289-6057
US cell +1-304-790-9192
Jamaica cell: +1-876-456-8898
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of david.reed via groups.io Sent: Friday, June 30, 2023 8:56 AM To: [email protected]Subject: Re: [nanovna-users] Connecting NanoVNA, antenna, and manual tuner Steven, [Transceiver], [Tuner], [Antenna] = [Nano], [Tuner], [Antenna] Set up if you wish to use your tuner to "adjust" your antenna resonant point with your Nano. David Reed, ac0yw
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Re: Connecting NanoVNA, antenna, and manual tuner
Steven,
[Transceiver], [Tuner], [Antenna] = [Nano], [Tuner], [Antenna] Set up if you wish to use your tuner to "adjust" your antenna resonant point with your Nano.
David Reed, ac0yw
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Connecting NanoVNA, antenna, and manual tuner
Hello all,
I would like to connect my NanoVNA, antenna and manual tuner (MFJ-969).
I can connect the nano and antenna but am not sure how to bring in the tuner.
An example of what I am trying to do can be found here:
at the 3:43 mark.
I have found several videos similar to the above video but unfortunately they don't show their connections.
Thank You,
Steven/kc3dow
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On Fri, Jun 30, 2023 at 12:58 AM, Roger Need wrote:
On Thu, Jun 29, 2023 at 11:58 AM, Mike wrote:
I made a new sending coil and it works a lot better now.
Looking better but you still have a large dip. Keep moving further apart
until you can barely see it and record the dip frequency as you go.
Roger
I moved the coil away until the frequency of the dip remained steady then moved a bit further. The vertical scale is 0.01dB/div so the dip is perhaps not as large as it seems. -- Mike?
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Re: NanoVNA with bigger screen
Pedro,
You write "I have a nanoVNA S-A-A-2 which is useless because it doesn't measure Rs orXs independently in S21 mode, only measures impedance complex."
Recent firmwares from DisLord provide what you need for SAA2N (also for H/H4) about all Z variant measurements in s21 mode.
Path menu is : DISPLAY / FORMAT S21 (THRU) / MORE
At this menu level you can choose SERIES R, SERIES X, SHUNT R, SHUNT X and more.
I have used succesfully these features for testing choke baluns. When it was not yet available, I proceed with external calculations (LibreOffice sheet) from s21 data file, but now you can display a graph in real time !
For sure, it does not provide a solution for a larger screen ... Please note that these s21 derived parameters are also displayed as discrete values in the right panel of NanoVNA-App (version 1.1.215 from DiSlord).
I have enclosed the last firmware bin file for V2/S-A-A-2 (480x320 display) from DiSlord, version 1.3.18, if you want to upgrade your VNA.
73 - Jean-Roger
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On Thu, Jun 29, 2023 at 11:58 AM, Mike wrote: I made a new sending coil and it works a lot better now.
Looking better but you still have a large dip. Keep moving further apart until you can barely see it and record the dip frequency as you go. Roger
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On 6/29/23 11:40 AM, Fran?ois wrote: Roger always has good ideas.
Attached is the measurement (via nanovna-saver) of a trape and I will then explain to you how the measurement is made.
When I read S11 Return loss I say it resonates at 18.085409 MHz. But look at the diagram S11 |Z|
Curious ? No ?.
73 I'd think somewhere between 18.082620 and 18.085096, because that's where the imaginary part goes through zero.
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On Thu, Jun 29, 2023 at 05:53 PM, Roger Need wrote: You are way too close to the coil being tested. The inductance of your coil
is affected by the proximity of another coil and this affects the SRF
measurement. Once you have a dip on the NanoVNA you need to keep reducing
the distance until the dip is barely seen. Then you measure the frequency. Roger I made a new sending coil and it works a lot better now. -- Mike
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Roger always has good ideas.
Attached is the measurement (via nanovna-saver) of a trape and I will then explain to you how the measurement is made.
When I read S11 Return loss I say it resonates at 18.085409 MHz. But look at the diagram S11 |Z|
Curious ? No ?.
73
--
F1AMM
Fran?ois
De la part de Roger Need via
Envoy¨¦ : jeudi 29 juin 2023 18:53
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Bob AF9W
Roger Need
