Hameg Analog Oscilloscope

[Carl-NC]

Arghhh! Arghhhh! [bashes head against PC screen yet again Smiley]
1 ) When Carl says "If you're NOT getting waveforms like this: "EqBeachPark.png" .. then you're doing it WRONG"
he's misleading you.

I agree with the head-bashing, but I am not misleading anyone.

I've said it a dozen times... STOP LOOKING AT THE COIL VOLTAGE... LOOK AT THE COIL CURRENT.

If you don't know how to do this, then find something else to do.

[Skippy]

I think Nino was trying to get waveforms that looked like your sawtooth one, which he's not going to get easily, as he's inexperienced.
Presumably Mr. Green's suggestion of using a 10R load is to approximate the probe you use.

[green]

I think Nino was trying to get waveforms that looked like your sawtooth one, which he's not going to get easily, as he's inexperienced.
Presumably Mr. Green's suggestion of using a 10R load is to approximate the probe you use.

That was my thought. Don't know if signal would be high enough to see on the scope with a low enough resistor. I asked why current waveform is more important than voltage waveform in the other thread measuring the Equinox coil current. Didn't get an answer, still trying to figure why. I have ITMD, maybe someone could suggest a page to look at. Tried a simulation in spice with a square wave, seems like voltage recording as good as current recording. Know little about VLF so probably not looking for the right thing.

triangle

[Carl-NC]

I asked why current waveform is more important than voltage waveform in the other thread measuring the Equinox coil current. Didn't get an answer, still trying to figure why.

The current waveform is exactly the same as the magnetic field waveform that gets transmitted. Except for sinusoids, the voltage waveform is not. Plus, in MF detectors, the current waveform is far easier to analyze than the voltage; just compare BBS voltage & current.

[EL NINO]

When measuring I tried to use a paralelly placed 330 R resistor, the sweep coil is located very close to the Equinox coil in Park2 program:






I also tested the frequency measurement in Math -FTT in program Park2:

[Skippy]

That's better.
I have marked on one of your waveform captures where the wave repeats. It takes 15 cycles of the dominant 39 kHz signal to repeat, every 385 microsecs.

[green]

The current waveform is exactly the same as the magnetic field waveform that gets transmitted. Except for sinusoids, the voltage waveform is not. Plus, in MF detectors, the current waveform is far easier to analyze than the voltage; just compare BBS voltage & current.

Tried some spice simulation to see if I could understand what happens. Some thoughts.

square Tx right chart: stepped Tx coil R(.1 and 3ohms). With constant Tx voltage, Tx current is constant rate(I/T=E/L)not effected by on time. Increased Tx coil R causes rate to decrease with time(IR drop). EL NINO's scope picture shows flat top, high L/R Tx coil? Easier to see the R effect in the voltage trace, maybe doesn't matter?

left chart: stepped target TC(10, 100 and 1000us). Rx voltage trace same as Tx voltage trace inverted for the 1000us TC target. Rx voltage for lower TC targets droop with time, 1000us TC target would with enough time.

square Tx_2 stepped target TC(1, 10, 100 and 1000us)

right chart: Rx current(R1 one ohm). Rx traces for higher TC targets same as Tx current trace inverted. Traces for lower TC targets increase with time, flatten out and decay.

left chart:Rx volts(R1 1k ohms). Rx traces for higher TC targets same as Tx voltage inverted.Traces for lower TC targets decay with time.

Do simulations make sense?

Carl, are you suggesting the detector should look at Rx coil current or just the pickup coil for recording Tx coil current with a scope?

[Mark-VA]

I agree with the head-bashing, but I am not misleading anyone.

I've said it a dozen times... STOP LOOKING AT THE COIL VOLTAGE... LOOK AT THE COIL CURRENT.

If you don't know how to do this, then find something else to do.

I'm going to crack out my old electronics book and give it a little extra study.
But why should I care about this subject?
It's because I really like to know or rather better understand what is actually being transmitted.

[Skippy]

You also need to know what is being received. The TX coil's magnetic field matches it's current, and its current is the integral of the voltage applied to it, hence why the square wave voltage produces the linear ramp up/down triangle wave current. The RX coil is a differential sensor, so applying a triangle-wave magnetic field to it will produce a square(ish) output voltage. This is what happens when you use a wire coil as a pickup coil to measure the transmitted signal. There's an integration, followed by a differentiation, which pretty closely cancel out, so you see the square wave on your receive coil.

[Carl-NC]

Do simulations make sense?

You're on your way to designing time-domain single or multi-frequency detectors!

Carl, are you suggesting the detector should look at Rx coil current or just the pickup coil for recording Tx coil current with a scope?

There are 3 potential approaches:

1. Use a current probe; they are expensive so most people won't have this option.
2. Add a small series resistor, 0.1 - 0.5 ohms. This is really easy and, though it does very slightly change the waveform, it is probably unnoticeable.
3. Use a pick-up coil, connected in a current-mode amplifier.

I have a current probe that I use for development purposes, but when I want to measure the TX waveform of an off-the-shelf detector, I use the pick-up coil.

[EL NINO]

In the following measurements I used a parallel 10 ohms ( Mr Green s" suggestion) resistor:

Program Park1:
Program Park2:
ProgramBeach2:
Program Gold1:
Program Gold2:

[EL NINO]

Measurements I used a FFT:

Program Park1:
Program Park2:
Program Field1:
Program Field2:
Program Beach1:
Program Beach2:
Program Gold1:
Program Gold2:
Program Gold2: 1F 20 khz
Program Gold2 1F 40khz

[EL NINO]

I am not have ... currently available Resistor with 1ohm or resistor 0.5 ohm - 0.1 ohm .. for further measurements ..., As soon as these resistors get .. so i repeat these measurements...

[Carl-NC]

In the following measurements I used a parallel 10 ohms ( Mr Green s" suggestion) resistor:

Much better!

[green]

More spice. Added a band pass filter with a Q of 10, I think. Easiest way I could think of in spice. 10kHz and 50kHz Tx. Don't see a difference between Rx current(R1=1) and voltage(R1=1k)other than phase shift compared to Tx voltage. Maybe band pass filter with a Q of 10 isn't the way to look at Rx? Not planning on building VLF, just trying to understand how.