Products > Test Equipment
Hantek 2000 series - 2C42/2C72/2D42/2D72
gf:
--- Quote from: mostorer on April 11, 2020, 08:25:11 pm ---In the next days I will review the DAC902E datasheet in order to check, based on current Rset, res on Iout and OpAmp gain, if the output is aligned to what it should be, then I will calculate a new value for Rset and will post my considerations.
In this moment an amplitude of 1V produces 1,25V on the output channel.
--- End quote ---
Nominally, it's trivial: 1.25V / 1.0V * 1780 Ohm => 2225 Ohm
+/- tolerance of the measured 1.25V, +/- tolerance of the 1.78k Rset, +/- tolerance of the new Rset
For better accuracy I suggest to measure the AWG output voltage with a DMM, since the (Hantek2000) scope is only specified with 3% accuracy, IIRC. Set AWG amplitude to 0 and the offset to say +1.5V, then to -1.5V, measure the two resulting AWG output voltages (-> DC) with a DMM and use (Vout@+1.5V - Vout@-1.5V) / (2 * 1.5V) as scaling factor for Rset.
If you have a DMM which is more accurate than the tolerance of the resistor, you can furthermore measure the resistor instead of assuming its nominal value.
The drawback of calibrating gain with Rset in the analog domain is still the missing offset calibration...
EDIT:
The DAC902's contribution to the offset is supposed to be only +/-1.25mV at the AWG output(+/- 0.025% FSR), so I'd suppose anything beyond that to originate in the amp (due to insufficient CMRR of the differential amp circuit, and offset voltage/current of the opamp).
smat:
Hello all. New 2c42 owner here. I am checking my hacking options here, or if anyone noticed what I did.
I tried to test the bandwidth of my scopes and my probes with a fast pulse, and a signal generator today, and it seems mine has far more than the claimed 40MHz bandwidth, probably 70Mhz or so.
Unfortunately I find it hard to tell, as there is some overshot and ringing going on, that really seems like an interpolation problem.
Unfortunately I can't get the pure ADC data out of the scope, as the display is interpolated and there are no options to change that, and even the PC software can only extract the interpolated waveform.
I wish I could get bare sample points on screen, perhaps with a linear interpolation to see more of the measurement, and less of the guesswork, but that may be just me.
I mean perhaps I could try lowering the time/div until every extracted sample corresponds to an ADC sample, but TBH I don't trust them I can get anything out of it that is not already "manipulated". I digress.
So. Did anyone do proper bandwidth tests of the 2x42, the 2x72 and a hacked 2x42? I really can't find my 40MHz limit in device, only this, what I think is a crappy interpolation artefact.
Above the 70-100MHz range it is the sample rate that limits the system anyway.
See attached picture. Good quality 10MHz signal fed in from a 50 ohm source through an 50 ohm BNC terminated coax. Looks "perfect" on a proper high bandwidth scope.
cliffyk:
--- Quote from: smat on June 10, 2020, 08:54:50 pm ---Hello all. New 2c42 owner here. I am checking my hacking options here, or if anyone noticed what I did.
I tried to test the bandwidth of my scopes and my probes with a fast pulse, and a signal generator today, and it seems mine has far more than the claimed 40MHz bandwidth, probably 70Mhz or so.
Unfortunately I find it hard to tell, as there is some overshot and ringing going on, that really seems like an interpolation problem.
Unfortunately I can't get the pure ADC data out of the scope, as the display is interpolated and there are no options to change that, and even the PC software can only extract the interpolated waveform.
I wish I could get bare sample points on screen, perhaps with a linear interpolation to see more of the measurement, and less of the guesswork, but that may be just me.
I mean perhaps I could try lowering the time/div until every extracted sample corresponds to an ADC sample, but TBH I don't trust them I can get anything out of it that is not already "manipulated". I digress.
So. Did anyone do proper bandwidth tests of the 2x42, the 2x72 and a hacked 2x42? I really can't find my 40MHz limit in device, only this, what I think is a crappy interpolation artefact.
Above the 70-100MHz range it is the sample rate that limits the system anyway.
See attached picture. Good quality 10MHz signal fed in from a 50 ohm source through an 50 ohm BNC terminated coax. Looks "perfect" on a proper high bandwidth scope.
--- End quote ---
Per Hantek's specs (see below) the "2000" series 'scopes (2D72, 2D42, 2C72 and 2C42) all have the same ≤ 5 ns rise time¹ specs at the BNC connector, and share the same 250MSa/s(Single-channel), 125MSa/s(Dual-channel) sample rate.
This leaves me to believe they share fundamentally the same "innards" and that the "model number bandwidth" indicated by the 3rd character of the model nomenclature is more related to establishing marketplace price points than to each model's actual instrument performance.
This is not unusual in mass manufacturing--General Motors did it for years. 20 or so years ago the lame stream media put it forth as some great "scandal" that Cadillacs used Chevy drive trains.
----------------------------------------------
¹ - Convention has it that bandwidth * rise time = 0.35; so bandwidth = 0.35/rise time--0.35 / 5e-9 = 70 MHz
gf:
--- Quote from: smat on June 10, 2020, 08:54:50 pm ---Hello all. New 2c42 owner here. I am checking my hacking options here, or if anyone noticed what I did.
I tried to test the bandwidth of my scopes and my probes with a fast pulse, and a signal generator today, and it seems mine has far more than the claimed 40MHz bandwidth, probably 70Mhz or so.
Unfortunately I find it hard to tell, as there is some overshot and ringing going on, that really seems like an interpolation problem.
Unfortunately I can't get the pure ADC data out of the scope, as the display is interpolated and there are no options to change that, and even the PC software can only extract the interpolated waveform.
I wish I could get bare sample points on screen, perhaps with a linear interpolation to see more of the measurement, and less of the guesswork, but that may be just me.
I mean perhaps I could try lowering the time/div until every extracted sample corresponds to an ADC sample, but TBH I don't trust them I can get anything out of it that is not already "manipulated". I digress.
So. Did anyone do proper bandwidth tests of the 2x42, the 2x72 and a hacked 2x42? I really can't find my 40MHz limit in device, only this, what I think is a crappy interpolation artefact.
Above the 70-100MHz range it is the sample rate that limits the system anyway.
See attached picture. Good quality 10MHz signal fed in from a 50 ohm source through an 50 ohm BNC terminated coax. Looks "perfect" on a proper high bandwidth scope.
--- End quote ---
Even after being degraded to some amount by the frontent, the pulse is still is "too fast" for the given sampling rate and contains too much high-frequency components >= fs/2. Therefore it violates the sampling theorem. Consequently a sinc interpolation can no longer reconstruct the original signal waveform exactly. An exact reconstruction is only possible if the original signal were band-limited to < fs/2 in the first place, before being sampled. The ringing in your picture is to be expected under this circumstances. I guess the "proper high bandwidth scope" has not just a higher bandwidth, but in particular a higher sampling rate as well? (and some scopes may also have a built-in anti-aliasing filter)
It is hard (if not impossible) to measure the step response of the frontent if the sampling rate is so low. Better sweep the frequency of a sine-wave signal and find the -3dB point (with a sine wave, you can go up to almost 125MHz without violating the sampling theorem (when the sampling rate is 250MSPS), and even beyond 125MHz you could still measure the amplitude of the down-converted sine wave).
smat:
--- Quote from: gf on June 11, 2020, 07:19:35 am ---Even after being degraded to some amount by the frontent, the pulse is still is "too fast" for the given sampling rate and contains too much high-frequency components >= fs/2. Therefore it violates the sampling theorem. Consequently a sinc interpolation can no longer reconstruct the original signal waveform exactly. An exact reconstruction is only possible if the original signal were band-limited to < fs/2 in the first place, before being sampled.
--- End quote ---
Thanks. I am not an expert on interpolation, but makes sense. Either limit the bandwidth - and I was wondering if the scope is more useful in BW limit mode at 20MHz, or change interpolation algorithm at a certain time/div value in firmware, which I seem to remember seeing in a cheap Chinese scope a few years ago. Interpolation options would be nice, but it's hard to get the balance right between usability and over complication, especially in a handheld.
--- Quote from: gf on June 11, 2020, 07:19:35 am ---I guess the "proper high bandwidth scope" has not just a higher bandwidth, but in particular a higher sampling rate as well? (and some scopes may also have a built-in anti-aliasing filter)
--- End quote ---
Yes, the digital has 1GS/s, and my analog has infinite. :D
--- Quote from: gf on June 11, 2020, 07:19:35 am ---It is hard (if not impossible) to measure the step response of the frontent if the sampling rate is so low. Better sweep the frequency of a sine-wave signal and find the -3dB point (with a sine wave, you can go up to almost 125MHz without violating the sampling theorem (when the sampling rate is 250MSPS), and even beyond 125MHz you could still measure the amplitude of the down-converted sine wave).
--- End quote ---
I am not that bothered about the actual BW. The 40MHz claimed is plenty for the price, having more is good to know, but I think it is much more important to be aware that apparent spikes riding on top/bottom of fast edges may be just the artefact, and if they are important, verify, hook up a proper scope.
For most uses I will probably keep it in 20MHz limit which is still amazing for the price point and form factor, and then there is the 10mV/div minimum sensitivity, which asks for a fair amount of 1x probing anyway.
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