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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.

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

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

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

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

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

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

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?

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

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

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.

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

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
Envoyé : jeudi 29 juin 2023 18:53

On Wed, Jun 28, 2023 at 10:15 AM, Mike wrote:

I had to wind my pickup coil around the end of the inductor to get enough
coupling for a response.

The dip is fairly close to the SRF estimated by Coil64, which was 15.58MHz.

Mike,

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

Nanovna-F has 4.3 inch IPS screen and is much more readable outdoors.
--
Doug, K8RFT

On 6/28/23 3:30 PM, Pedro Madeira CT7AHV wrote:

Hello to all,
Thanks for all your inputs, I made a few searches and I saw the devices you
told.
Actually, I just need to work up to 150MHz, I build solid state amplifiers
and I need to tune the low pass filters. I also build antenna transformers,
Baluns, Ununs and RF chokes and need to measure them.
I have a nanoVNA S-A-A-2 which is useless because it doesn't measure Rs or
Xs independently in S21 mode, only measures impedance complex.

Isn't complex impedance Rs + Xs j?

But you said S21, which is also complex (although often displayed as magnitude and phase). But convertible to equivalent series R and X, with some math. There's been some discussion of this on the list, and it's not "instrument" dependent.



Tuning low

pass filters with this nanoVNA is also not possible because the measurements
are not accurate enough as my other VNA. I performed some comparisons and
the Transmission Loss in dB is very different, and yes I made proper
calibrations. The nanoVNA I have is just good enough to do SWR
measurements...

That seems odd.. how much rejection do you need to measure? (I'm assuming the passband isn't a problem). The little original NanoVNA does just fine at 60dB down, although I don't know that I'd want to commit to 1 dB uncertainty in the stop band.

The NanoVNA is probably not the right tool for aligning a 6 can diplexer for 2 meters.

My goal is to have a VNA independent of the use of a computer, that's why
I'm looking for a VNA with screen bigger than 3 inches! Which model should
be the most accurate? I know all these are Chinese devices, but maybe I can
find a reliable one for my works...

Well, yes - the tiny screen is a pain. I was checking some feedlines earlier this week outdoors and not only is the 3" screen hard to see, it's hard to take a picture of.

But if you're tuning something on a bench, it seems a computer isn't a deal breaker. I use a RPi to talk to a NanoVNA using NanoVNA-Saver, and it will display on as large a screen as you can plug in.

Thanks, best 73
Pedro Madeira
CT7AHV/C91AHV

Hello to all,
Thanks for all your inputs, I made a few searches and I saw the devices you
told.

Actually, I just need to work up to 150MHz, I build solid state amplifiers
and I need to tune the low pass filters. I also build antenna transformers,
Baluns, Ununs and RF chokes and need to measure them.

I have a nanoVNA S-A-A-2 which is useless because it doesn't measure Rs or
Xs independently in S21 mode, only measures impedance complex. Tuning low
pass filters with this nanoVNA is also not possible because the measurements
are not accurate enough as my other VNA. I performed some comparisons and
the Transmission Loss in dB is very different, and yes I made proper
calibrations. The nanoVNA I have is just good enough to do SWR
measurements...

My goal is to have a VNA independent of the use of a computer, that's why
I'm looking for a VNA with screen bigger than 3 inches! Which model should
be the most accurate? I know all these are Chinese devices, but maybe I can
find a reliable one for my works...


Thanks, best 73


Pedro Madeira
CT7AHV/C91AHV

I recently bought the SeeSii nanoVNA-H4 which has a 4" screen. I love the larger screen. It is useful up to 1.5 GHz, but my use for HF radio is just 3 to 30 MHz, plus VHF and UHF, so this is fine for me.

If you look at the nanoVNA menu structure map you will see that the H4 gets you some useful additional functions, including two more memory locations and 201, 301, and 401 sweep points options. The extra sweep points come at corresponding increase in sweep time, however.

As with all of the nanoVNA units, however, it is best to remember that the basic nanoVNA circuit design is open source, and you are getting what you pay for. Chief concern is component quality, shielding, and soldering.

73
Bob Rose "Zayde"
robert.rose@...
KN6UXD
DM13ld
SKCC 27222

Thanks Fran?ois for the response and taking the time. I wanted to put another plot on here, this is with another NanoVNAH4 I have and the outlier is in the middle of the sweep at ~130MHz. The calibration of the device does not get rid of it. I would like to know if there is a way to remove it experimentally or if anyone knows what the cause is.

On Wed, Jun 28, 2023 at 04:57 PM, EB4APL wrote:

Hi, I still keep a true GDO but I had nor used it for a long time.

When I built my Poor Ham Scalar Network Analyzer some years ago, I also
built a pickup coil wound in an old 35 mm film canister with a BNC
connector. I connect it to the Return Loss Bridge? and used it as a GDO
but much more convenient. When I got the nanoVNA I tested it with it and
the results are very good, you can measure the resonance of any? circuit
without physically connecting to it.? I uploaded some pictures to the
Photos section.

Ignacio

Nice job Ignacio. How many turns on your pickup coil?

I had to wind my pickup coil around the end of the inductor to get enough coupling for a response.

The dip is fairly close to the SRF estimated by Coil64, which was 15.58MHz.

Pictures attached.

--
Mike