XP Deus 2 Transmit frequencies

[Mark-VA]

This is the waveform of the General program Freq Max 14. Top right hand corner is the frequency counter measurement. The bottom frequency is the standard horizontal frequency measurements. This form doesn't change with any of the stock programs (1-12) if freq max 14 is selected. No difference
According to the user manual, "The hardware frequency counter supplied with the DS1000Z oscilloscope can make more precise measurement of the input signal frequency"




FTT measurements in purple, absolutely lost on how to read that.

I can only identify two different transmit frequencies for freq max 14. 4.46kHz and 8.92~kHz



But I can only see two distinct frequencies.

fyi if single frequency is chosen the counter frequency and bottom horizontal frequency agree. Example if 17kHz is chosen both counter and frequency match.

If any one would like to see additional scope measurements, please let me know.

[Carl-NC]

Frequency counters are designed for measuring single-frequency waveforms, they cannot handle complex waveforms.
On the FFT, you are looking at 50MHz/div which is way too far out. You need to zoom in to around 5-10 kHz/div. To do this, zoom out on the time domain waveform.
A square wave waveform is the easiest to analyze. A multi-period waveform that switches between 2 voltage levels is not too hard. But when you get into these multi-level multi-period waveforms they can be really difficult to figure out. For this, you now need to consider a current-mode probe instead of a voltage-mode probe. This will allow you to look at the actual magnetic field waveform instead of the driving voltage waveform.

[moodz]

This is the waveform of the General program Freq Max 14. Top right hand corner is the frequency counter measurement. The bottom frequency is the standard horizontal frequency measurements. This form doesn't change with any of the stock programs (1-12) if freq max 14 is selected. No difference
According to the user manual, "The hardware frequency counter supplied with the DS1000Z oscilloscope can make more precise measurement of the input signal frequency"




FTT measurements in purple, absolutely lost on how to read that.

I can only identify two different transmit frequencies for freq max 14. 4.46kHz and 8.92~kHz



But I can only see two distinct frequencies.

fyi if single frequency is chosen the counter frequency and bottom horizontal frequency agree. Example if 17kHz is chosen both counter and frequency match.

If any one would like to see additional scope measurements, please let me know.

Your FFT is set to 50Mhz per division ... you have no hope of resolving 17 khz. Select FFT ( math ) channel and adjust time base to something like 10 Khz per division.

The frequency counter on the scope works like any regular frequency counter. Its edge triggered and can only resolve one frequency if the edge transitions are "clean".

It cannot resolve frequencies from mixed signals.

EDIT : As Carl pointed out already

[JoyJo]

Greetings. Good job, Mark-VA! Can I ask for more information: increase the resolution of the spectrum. It is better to consider such a complex signal from the point of view of the spectrum. You have a resolution for the spectrum set to 50, set it to 10.

[moodz]

... sometimes RTFM works also.

[Mark-VA]

I was assured from one of the Rigol reps that the scope I purchased could easily detect and measure multi frequencies from a metal detector. I explained what I was needing and their answer was any of the DS1000Z series scopes. Was not planning on spending a huge amount of extra money for a current probe. I'll gladly adjust the time division on the FTT and see what I get.
Current probe could easily cost more that the scope I bought.

Now back to the scope images I posted, if the scope can't capture the frequency of more that one wave at a time what is the two different frequencies in the image represent?
To me, in this image they're clearly 2 peak frequencies (square waves), correct?

Please elaborate and explain if I'm not correct.

[Carl-NC]

You don't need to buy a current probe, you can make a current-mode field probe for a few dollars. Here is the basic schematic:



For starters you can wind your own coil, its resistance and R set the gain of the circuit. Start with R=100.

[Mark-VA]

I don't see a schematic sir.
I thought about running one side of receiving coil through this choke then reattach. Then connect the scope to the leads on the choke.

[Carl-NC]

I don't see a schematic sir.
I thought about running one side of receiving coil through this choke then reattach. Then connect the scope to the leads on the choke.

This would give you a waveform that is the derivative of a derivative, not what you want. See if my last post is now fixed.

[Mark-VA]

yes, thank you

[Mark-VA]

You don't need to buy a current probe, you can make a current-mode field probe for a few dollars. Here is the basic schematic:



For starters you can wind your own coil, its resistance and R set the gain of the circuit. Start with R=100.

Okay starting from L which I'm assuming is my pickup coil.
L connects to the ground probe terminal.
other L connector (my pickup coil) goes to R at 100 ohm and also feeds the inverting - input
Other end of R will connect to op amp output which also connects to the positive end of the probe.
+ input to ground clip on the probe.

Any particular op amp chip
I see now I have a very important need of a good breadboard not just a bunch of connected wires.
Hey Amazon has some cheap breadboard kits for under $20 and they usually have a power supply too.

[Carl-NC]

The opamp needs at least several MHz of GBW product. You might be able to get away with a TL071. The opamp needs bipolar power (say, +/- 5V). Yes, a breadboard is very useful for stuff like this.

[Mark-VA]

Using the current probe schematic.
Assuming the coil in the schematic is my pickup coil.
I have the following is the captured wave of:
R=
3.3 ohm
50 ohm
75 ohm
100 ohm
180 ohm
If this is wrong then the amp may not be adequate.

[Carl-NC]

The first one is closest to being right. What opamp?

[Altra]

I wired up one yesterday. It works well for a first try. I tried a TL072 and NE5532 both worked. The NE5532 seemed to be cleaner. The pickup coil is 520uh, 1 ohm. This is a nice tool for the work bench.

Equinox 800 tx current in park mode. I also tried the prospecting mode 40khz and was able to see the saw tooth current wave.







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