Matching the impedance of the intermediate cable in P.I detectors to the coil impedance.

[profesor]

merhaba, hesabımda 500uH bobinin 1 kHz frekanstaki empedansını 3.14R olarak buldum.
RG 58U koaksiyel kablo 50R. bu durumda empedans eşitlemesi yoktur.
Sanırım enerji SWR'yi geri yansıtıyor.
Bu sorunun ??z?m? i?in fikirlerinizi arzuluyorum.
Teşekk?r ederim.

[Qiaozhi]

merhaba, hesabımda 500uH bobinin 1 kHz frekanstaki empedansını 3.14R olarak buldum.
RG 58U koaksiyel kablo 50R. bu durumda empedans eşitlemesi yoktur.
Sanırım enerji SWR'yi geri yansıtıyor.
Bu sorunun ??z?m? i?in fikirlerinizi arzuluyorum.
Teşekk?r ederim.

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[profesor]

hi, in my account I found the impedance of the 500uH coil at a frequency of 1 kHz to be 3.14R
RG 58U coaxial cable 50R. in this case there is no impedance equalization.
I think the energy is reflecting SWR back.
The solution of this problem? I desire your ideas for you.
Thank you.

[WM6]

I think the energy is reflecting SWR back.

Here you should read about Near Field propagation theory and not about SWR.

[profesor]

Here you should read about Near Field propagation theory and not about SWR.

I read the near field article.
I guess it's not the answer to my question.
Thank you.

[dbanner]

hi, in my account I found the impedance of the 500uH coil at a frequency of 1 kHz to be 3.14R
RG 58U coaxial cable 50R. in this case there is no impedance equalization.
I think the energy is reflecting SWR back.
The solution of this problem? I desire your ideas for you.
Thank you.

I knew one day this question would provide the perfect scenario to reply with a piece of information l didn't understand conceptually at the time.

The coil( inductor) consists of both the cable and the coil, together as one.
The cable is part of the coil!( For the purposes of near field)
Therefore the impedance of the coil must be calculated with cable attached to coil. They are considered as one coil, together.
The inductance is therefore derived from srf tests computed with the cable attached. After all, this is the cable which will be attached to the coil when in actual use and throughout the coils life. They cannot be separated because the cable has capacitance which affects the overall numbers.
Think of it as merely a coil with long leads. But one coil nonetheless.

[dbanner]

One thing I forgot to mention, a metal detector coil is NOT an antenna!

[profesor]

I knew one day this question would provide the perfect scenario to reply with a piece of information l didn't understand conceptually at the time.

The coil( inductor) consists of both the cable and the coil, together as one.
The cable is part of the coil!( For the purposes of near field)
Therefore the impedance of the coil must be calculated with cable attached to coil. They are considered as one coil, together.
The inductance is therefore derived from srf tests computed with the cable attached. After all, this is the cable which will be attached to the coil when in actual use and throughout the coils life. They cannot be separated because the cable has capacitance which affects the overall numbers.
Think of it as merely a coil with long leads. But one coil nonetheless.

close to the answer to the question.
But the harmonics of 1khz pulse extend up to 100khz.
The 50R rg 58 u behaves like a transmission line, not like a coil.
Impedance matching is necessary in my opinion.

[WM6]

But the harmonics of 1khz pulse extend up to 100khz.

.

Even with 100kHz it is about wavelength of 3km (or 3000m) with barely sensing harmonic f amplitude,
which mean that SWR is here practically nonexistent.

At 1kHz, wavelength is about 300km (or 300000m). 1m of cable (+ or -) at 300000m mean nothing in term of measured SWR.

All AC driven conductors/inductors (inclusive cable of any length) are some sort of radiating antenna, without exception.
In contrast to antennas that produce distant wireless transmission, EM waves in coax-cable are confined and offer confined transmission.
Antennas act as distant (Far-Field) EM wave (eg radio-wave) radiator and coax-cable act as EM wave wave-guide in first line.
Conductor/inductor to be able to radiate Far-Field EM wave, need to be resonant at radiating frequency.
Conductor to be resonant at given frequency, mean, that it enable AC magnetic and electric component (field) of wave, to be in balance.
Without antenna resonance at given frequency, there is no Far-Field radiation (par example: no radio wave at radio frequencies).
But even with conductor/inductor total out of resonance at driven frequency, there is always Reactive Near-Field radiation around those "antenna".
So in case of MD coils, we can primary talk about Reactive Near-Field region of radiation.
Short coax cable confined radiation do not significant imply by SWR at working frequency to coil characteristic.
In Reactive Near-Field region of antenna radiation mess, SWR is hard to calculate (or to measure) quantity.