waveform attenuation with usb scope

Discussion in 'Test & Measurement Forum' started by hobbyist, Oct 20, 2017.

  1. hobbyist

    Thread Starter AAC Fanatic!

    Aug 10, 2008
    884
    85
    Quick question for anyone out there,
    I just purchased this,
    Hantek HT6022BE20Mhz 6022be PC Based USB Digital Storage Oscilloscope, 20 MHz Bandwidth, and I'm using it to experiment with LC tuning circuits, I built a simple CE amplifier for this tuned circuit to feed into, and checking for gain on the output.

    Now first I am using my 100MHZ analog oscilloscope, and checking input,output waveforms, everything looks normal with gain.

    When I hook up my usb scope in place of the analog scope, the waveforms are impeded and both input and output waveforms drop, and it shows close to unity gain on the waveform.

    Both scopes have the same input impedance of 1Mohm, and 25pf, I switched probes and still got the same results, analog no attenuation, usb scope attenuation on the waveforms.

    My analog scope has both AC and DC inputs, the usb has only DC input.
    I have capacitor coupling for the signals to both probes.

    My question is this, can this be expected from a very inexpensive usb scope $55, or is this just inherent with DSO oscilloscopes.

    Thanks for any advise on this issue.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    8,751
    2,020
    Is the bandwidth specified in the same way for both scopes (i.e. is it the -3dB point or the unity-gain point which is relevant)?
    What frequency is the input?
     
  3. hobbyist

    Thread Starter AAC Fanatic!

    Aug 10, 2008
    884
    85
    Thank you for your help.

    It is the unity gain, because on my analog scope I show about Av~5.
    The usb scope, drops the input around half and brings the output close to the same value.

    I did this first with my usb scope and discovered this, then I tried my analog scope and got no attenuation, so then I kept the analog scope on, and hooked up the usb probes and seen the waveforms attenuate on the analog scope as well.

    Remove the usb and the analog goes back to normal Av5 and no attenuation to either waveform.

    On my analog 100Mhz scope : 20Mhz bandwidth.
    usb scope says 20Mhz bandwidth.

    here are the usb specs:

    2 Channels Bandwidth: 20MHzShot bandwidth: DC to 20MHzInput Impendence: 1Mohm 25pFMax. Sample rate: 48MS/vertical resolution: 8BitGain range: 20mV-5V, 8StepsDC accuracy: ±3%Time base range: 1ns-9000s, 39 Steps Vertical adjustable: Yes Input protection: Diode clamping-Y: Yes Trigger Mode: Auto, Normal and Single Trigger Slope: +/-Trigger level adjustable: Yes Trigger Type: Rising edge, falling edge Trigger Source: CH1, CH2Pre/Post trigger: 0-100%Sampling selection: Yes Waveform Display: port/line, waveform average, persistence, intensity Network: Open/Close Vertical mode: CH1, CH2, Dual, ADD Cursor measurement: Yes Math: FFT, addition, subtraction, multiplication, division. Cursor: Frequency, Voltage
     
  4. hobbyist

    Thread Starter AAC Fanatic!

    Aug 10, 2008
    884
    85
    Thankyou very much for helping me.

    I got this figured out now, my analog probes were set to X10 and that gave me my proper Av.
    My usb probes were set on the X1 and that gave my loss of gain signals.

    I set my analog scope probes to the X1 setting and got the same attenuation waveforms just as shown on my usb scope.

    It is the probe settings thats attenuating the signals on both scopes.

    When all probes are set to X10 the waveforms are no longer attenuated.

    The usb scope works good it shows the same waveforms as the analog scope.

    Thanks again.
     
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