TX Drivers Compare

[pito]

right? = wrong, valuable is info how much energy is coming out of Tx coil not how much you put to it, that depends to quality of the coil.
you can't directly compare 10kHz & 15kHz TX fields. To do that you need a current-mode probe = not sure about that ?

[Carl-NC]

Actually, I already use this method, but I think there is no need for this coil to learn this information. I can already see the same data through the PCB with an oscilloscope, right? I'm actually researching what I can look at differently in terms of performance criteria.

In some cases, you can probe the TX voltage on the coil and get relative performance, in some cases not. For example, the same TX circuit driving a 10" coil and a 6" coil will likely have the same TX coil voltage, but the field strengths will be completely different.

[Carl-NC]

you can't directly compare 10kHz & 15kHz TX fields. To do that you need a current-mode probe = not sure about that ?

A voltage-mode pickup coil shows you the derivative of the field, which means the amplitude is proportional to frequency. A current-mode probe shows the raw field strength, independent of frequency.

[pito]

amplitude is proportional to frequency = let see, random Tx coil, frequency from 20 kHz to 5 kHz

Resonance at 12 and 6.2 kHz, the rest of the band is more or less flat.

[profesor]

What kind of device would you recommend for pulsed signals?
or what a composite device should be like.

[pito]

And I think the coil and oscilloscope should work, the simplest = just speaker, short the speaker terminals with a loop (20cm)
https://www.youtube.com/watch?v=txe78PQwzj8
14:20

[Carl-NC]

amplitude is proportional to frequency = let see, random Tx coil, frequency from 20 kHz to 5 kHz
Resonance at 12 and 6.2 kHz, the rest of the band is more or less flat.

For a constant voltage driven TX coil, as you increase the frequency the TX current decreases (I = V/wL), and so the TX field strength decreases. At the same time, the induced RX voltage is proportional to the derivative of the TX field (ε = -N*A*dB/dt), which is decreasing in amplitude but increasing in frequency, so the RX voltage stays constant. So even though you see a constant amplitude on the pickup coil with increasing frequency, the TX field is steadily decreasing. That is why you cannot directly compare pickup coil results at different frequencies.

[pito]

Let see part 2
With frequency changing meter needle doesn't move. I agree with theory, the current should change but is not. I may investigate that some day.

[pito]

Let see part 3
Instead a coil I using piece of wire, ANT straight to the oscilloscope.


top ANT = no amplitude change
bottom pickup coil = no amplitude change

[Carl-NC]

With frequency changing meter needle doesn't move. I agree with theory, the current should change but is not. I may investigate that some day.

What current are you measuring? The overall TX circuit current, or just the current through the coil?

[pito]

What current are you measuring? The overall TX circuit current, = generator total current current, = 100mA.
I have also 1 Ohm resistor in Tx driver, used as current sensor, it is showing 0 mA, so current it is very small, for instance another coils can drawn over 100mA (at resonance ). The coil is 70 turns, 3mH, capacitor in series with coil 1000uF.

[Daves]

What current are you measuring? The overall TX circuit current, or just the current through the coil?

Hi Carl,
I want to ask something,
Why are square waves used in TX drivers? I do not say TX as a driving signal, a square wave is seen at the TX output and RX input, it can do the same with sine.

Also, why do simultaneous products always have square wave transmit and receive?

[Carl-NC]

You can drive the TX coil with a sine wave voltage or a square wave and get equivalent results. The sine wave is a little more efficient but for, say, a variable frequency detector the square wave is easier. In multifrequency, the square wave is much much easier.