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Just 4 turns. The idea and constructive details came in 2015 from Jim Giammanco N5IB, the original designer of the PHSNA.

Ignacio

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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.

.

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?

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

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

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

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Ah, the old days! It's been 50 years since I've used a GDO (when G = grid!).

I'll give that a go, thanks.

--
Mike

On Tue, Jun 27, 2023 at 05:54 AM, Mike wrote:

I compared both methods of calibration, which I refer to as "screws" and
"crocs".

At around 72kHz, where the reactance is approximately 50R, both calibration
methods give an inductance of 108uH. However, the SRF was 7.4MHz for "screws"
and 12.9MHz for "crocs".

I then repeated the measurement with a different VNA, an FA-VA5. This gave
L=110.7uH for "screws" and 110.5uH for "crocs". The SRF was 6.38MHz for
"screws" and 6.45MHz for "crocs".

I can accept the difference in L between the two devices but can't decide
which one is giving me the most accurate SRF.

With a 110 uH coil it takes 4.2 pF to resonate at 7.4 MHz. and 1.4 pF to resonate at 12.9 MHz. That is a difference of 2.8 pF which is not much.

One way to get to the bottom of this is to short the terminals of the coil together and then "grid dip" it like the old days. You can do this with the NanoVNA by making a pickup coil at the end of a short connecting cable. Calibrate over 5 to 15 MHz. in the usual manner. Set the trace to S11 Log (Return Loss setting) Then attach the pickup coil to the NanoVNA and place the 110 uh coil and the pickup coil in parallel a short distance apart. Look for a dip in the trace. Keep moving the coil further away until the dip has just about disappeared. Now move a marker to the dip and the frequency should be very close to the SRF.

Roger

What I wanted to do is not working.

I have an Excel sheet that allows me from the S11 of an antenna to determine its L and C near the resonance by pressing the curve of a plug to pass through two points.

In your case, it works at resonance but we already know the values involved. Far from resonance the results are not good.
--
Fran?ois

De la part de Mike
Envoyé : mardi 27 juin 2023 15:00

On Tue, Jun 27, 2023 at 09:02 AM, Fran?ois wrote:

Could you post your .s1p file in shunt on port 0. I would like to reger
something.

Have you noticed that when you connect a coil or a trap (finally a dipole) by
a single leg on port 0 (the other leg in the air), looking at the ROS, you can
see the resonance very well. Ok, it only gives elements at the resonance
frequency... but still it's very practical
73
--
F1AMM
Fran?ois

-----Message d'origine-----

De la part de Mike
Envoyé : lundi 26 juin 2023 10:23

Hi Fran?ois

Here is the .s1p file for a range of 1 to 20MHz.

--
Mike G8GYW

On Mon, Jun 26, 2023 at 05:25 PM, Roger Need wrote:

I suggest you calibrate right at the screw terminations on the green block
with the alligator clip leads removed. Then attach the leads and make your
measurement. From the photo it looks like the leads are about 4" long and
each one will add about 100 nH of inductance (total 200 nH or 0.2 uH). That
extra .2 uH when you are measuring 110 uH is not significant. However you
should get a better estimate of the SRF and be able to calculate the parasitic
capacitance to more accuracy.

Try it and see what you find...

Roger

Roger

I compared both methods of calibration, which I refer to as "screws" and "crocs".

At around 72kHz, where the reactance is approximately 50R, both calibration methods give an inductance of 108uH. However, the SRF was 7.4MHz for "screws" and 12.9MHz for "crocs".

I then repeated the measurement with a different VNA, an FA-VA5. This gave L=110.7uH for "screws" and 110.5uH for "crocs". The SRF was 6.38MHz for "screws" and 6.45MHz for "crocs".

I can accept the difference in L between the two devices but can't decide which one is giving me the most accurate SRF.

--
Mike

Could you post your .s1p file in shunt on port 0. I would like to reger something.

Have you noticed that when you connect a coil or a trap (finally a dipole) by a single leg on port 0 (the other leg in the air), looking at the ROS, you can see the resonance very well. Ok, it only gives elements at the resonance frequency... but still it's very practical
73
--
F1AMM
Fran?ois

On Mon, Jun 26, 2023 at 05:25 PM, Roger Need wrote:

Calibrating with the crocodile clips will not give you a good reference plane.
The reason I say this is if you keep them the same distance apart when you
cal with an open, short and load you will have considerable inductance in the
short and 50 ohm "cal loads". If you calibrate with the clips close together
and then spread them the reference plane has changed. Neither is a good
option.

I suggest you calibrate right at the screw terminations on the green block
with the alligator clip leads removed. Then attach the leads and make your
measurement. From the photo it looks like the leads are about 4" long and
each one will add about 100 nH of inductance (total 200 nH or 0.2 uH). That
extra .2 uH when you are measuring 110 uH is not significant. However you
should get a better estimate of the SRF and be able to calculate the parasitic
capacitance to more accuracy.

Try it and see what you find...

Roger

Thanks Roger, I will try that tomorrow.

--
Mike

On Mon, Jun 26, 2023 at 01:23 AM, Mike wrote:

This is my test fixture, calibrated at the croc clips. It's not ideal but I'm
limited by the length of the coil. Should be OK at my measurement frequency of
70kHz though!

Calibrating with the crocodile clips will not give you a good reference plane. The reason I say this is if you keep them the same distance apart when you cal with an open, short and load you will have considerable inductance in the short and 50 ohm "cal loads". If you calibrate with the clips close together and then spread them the reference plane has changed. Neither is a good option.

I suggest you calibrate right at the screw terminations on the green block with the alligator clip leads removed. Then attach the leads and make your measurement. From the photo it looks like the leads are about 4" long and each one will add about 100 nH of inductance (total 200 nH or 0.2 uH). That extra .2 uH when you are measuring 110 uH is not significant. However you should get a better estimate of the SRF and be able to calculate the parasitic capacitance to more accuracy.

Try it and see what you find...

Roger

This is my test fixture, calibrated at the croc clips. It's not ideal but I'm limited by the length of the coil. Should be OK at my measurement frequency of 70kHz though!

--
Mike

On Sun, Jun 25, 2023 at 03:15 PM, Roger Need wrote:

The VNA can only measure R + jX or R//jX (with later firmware versions). It
calculates inductance by dividing X by 2*pi*frequency and this ONLY gives an
estimate of the true coil L if the coil is air wound and the frequency is low
enough that the skin effect is not having much effect on underlying
inductance.

Roger, the method I suggested requires inductance calculated this way. It yields an accurate coil model over a narrow frequency range. To my surprise, it seemed good enough over the whole 3.5-4 MHz band. But the wideband model suggested in the writeup noticeably improved accuracy over the somewhat wider 88-108 MHz band.

Brian