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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.

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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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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.

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Mike

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

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
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F1AMM
Fran?ois

De la part de Roger Need via
Envoyé : jeudi 29 juin 2023 18:53

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

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 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 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?

Equivalent circuit=Spice model is not same as impedance. VNA gives you impedance, Coil64 and give you equivalent circuit. Or an approximation of it.

.

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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