July 31, 2013
about a year ago
The analog bandwidth is not listed, not even in the Wiki. Based on an analysis of the circuit, the analog channels are 4.4MHz -3dB bandwidth. In addition, there are a lot of these scopes out there with an incorrectly specified TVS protection diode on the digital channels that limits their bandwidth to under 1MHz.
Also, this is NOT 72Msps per channel, It is dual 36Msps ADC converters.
Nyquist has nothing to say about bandwidth of a scope. Clearly, you cannot represent a sine wave with only two samples. It takes more like 8 or 10. That fits with a 4.4MHz bandwidth with 36Msps.
In addition, square waves require at least the 5th harmonic to approximate, more like 9th harmonic if you want any reasonable representation of the rise time. One of the requirements of a square wave is rise time. The rise time of the scope must be several times faster (shorter) than the rise time of the square wave, or it affects how the actual rise time is displayed.
There is another requirement with square waves: You are often using a scope on them to look for glitches, overshoot, and ringing. Those things will have a spectral bandwidth many times greater than that of the square wave. For that, the two digital channels are useless.
I consider a 4.4MHz scope barely adequate for audio work and sub100kHz digital signals.
The function generator is primitive. Sine, triangle, and sawtooth waveforms look like they are generated from only 3 or 4 bits of information, with big noisy steps between levels. They are stairstepped, is what I’m saying.
Over 20 years an Electronics Technician, and an Electronics Engineering Technician.
about a year ago
Yes, because it is embarrassingly low. Based on an analysis of the circuit, the analog channels are 4.4MHz -3dB bandwidth. In addition, there are a lot of these scopes out there with an incorrectly specified TVS protection diode on the digital channels that limits their bandwidth to under 1MHz.
about a year ago
They still require a resistor. If you are running them off of batteries without a resistor, then you are relying on the internal resistance of the batteries and the LED to limit current, a dangerous way to run LEDs.
So they may work on a Lithium coin cell, or two AA batteries, but burn out on a Lithium Ion rechargeable or a couple of C cells.
about 2 years ago
I know this is old, but for those who may find this:
The input offset voltage is amplified along with the signal, that is why you will see a large output with no input.
A 741 has offset null terminals. Connect the outer terminals of a 10k trim potentiometer from pin 1 to pin 5. Connect the center slider terminal of the trim pot to the negative supply voltage, or to ground. You really need to use both positive and negative supply voltages with the 741, unless the signal you are amplifying is a couple of volts above ground already. The 741 was not designed to work well with a single supply.
In any case, for amplifying a signal this small, you will really want to use either a newer Op Amp with input offset voltage in the range of nV, find one with offset adjust terminals, figure out how to add offset compensation externally, or use a chopper amplifier.
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