USB cable shield resistance technical measurements

Discussion in 'Portable and Other Gear Measurements' started by atomicbob, Jan 15, 2018.

  1. skem

    skem Friend

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    I agree. Those are all valid considerations.

    Your cable-only R measurement of Pyst agrees with mine now, so that's encouraging in terms of consistency between cables.

    I think a table of C measurements, even if done quickly and at 100-200 kHz, , would be interesting. At least for the two or three best cables .. since you have the setup and the B&K already.

    Thanks Bob! I appreciate the goodwill!
     
  2. AllanMarcus

    AllanMarcus Friend

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    This is quite fascinating. Other than extrapolation as to the quality of the rest of the cable, what do these measurements signify regarding sound quality? Thanks
     
  3. SquiGGlez

    SquiGGlez Acquaintance

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    I was going to ask how is a simple resistance measurement indicative of a cable's shielding effectiveness and started googling a bunch of crap on transfer impedance until I got to the part where Bob said it was just to measure the quality of the connection between the shielding and the connector.

    I suppose this is a pretty simple and novel way that pretty much anyone can use to get an idea of a cable's build quality.

    Hopefully you can unearth some gems among the dirt cheap garden variety USB cables.

    Now that I think about it I'm kinda surprised blue jeans doesn't make one.
     
  4. atomicbob

    atomicbob dScope Yoda

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    Part II - USB Cable Shield Resistance measurements

    8 USB cables were evaluated for shield resistance to A and B end connectors.

    The lineup (01, 05, 08 are repeats from Part I for reference):
    01 generic clear small shield - 75 cm
    05 Audioquest Forest shield - 75 cm
    08 Schiit Pyst shield - 100 cm
    09 Schiit Pyst shield - second sample - 100 cm
    10 Audioquest Pearl shield - 150 cm
    11 Audioquest Carbon shield - 75 cm
    12 Wireworld Ultraviolet 7 shield - 75 cm
    13 Monoprice shield - 100 cm


    Data were acquired using the following:
    Keysight 34461A 6.5 digit DMM with Benchvue for data logging
    4-wire resistance measurements with sense at the breakout PCB terminals
    APRS World USB A breakout board
    APRS World USB B breakout board
    Optic Bench Plate with risers, posts and clamps to immobilize A and B connectors

    Each cable tested had both A and B ends inserted twice into the breakout boards to assure removal of any oxidation on the shield connection. Then A and B ends were secured into the clamps preventing any movement of the USB cables with respect to the breakout board connectors. A positive pressure existed assuring both A and B connectors made positive contact with breakout board connectors. This is different from Part I, which was more representative of actual cable connections with USB devices. As such, resistances will be lower across the cable to breakout board connection.

    4-wire resistance measurements is also different from Part I. This effectively eliminates the resistance of the test fixture connectors to the DMM.


    Each cable was measured over a period of 10 minutes.
    Each cable was subjected to a mild cable disturbance (squeeze test) approximately 5 cm from connector for a period of 3 seconds, 3 times during a 1 minute data acquisition.

    Measurement Setup (Part II):
    DSC_0002a.jpg


    Results:

    10 Minute no cable movement:
    20 20180205 USB Cables shield R - all.png
    Monoprice is definitely plays in a space of it's own, not even close to the others. The wandering resistance, even though the cable is motionless and secured, is not reassuring.

    Y-axis zoom
    21 20180205 USB Cables shield R - 50 to 150 mOhms.png
    These are all much better performers.


    1 Minute with three 3-second squeeze tests:
    22 20180205 USB Cables shield R - all - squeeze test.png
    Monoprice did not do well at all. I'd rather not use this USB cable.


    Y-axis zoom 1
    23 20180205 USB Cables shield R - 50 to 250 mOhms - squeeze test.png
    The generic clear small shield USB cable is on the fence. Pearl is a bit more predictable and appears to return to a stable state after each disturbance. Still, I'd rather have any of those below it as zoomed in the next graph.

    Y-axis zoom 2
    24 20180205 USB Cables shield R - 50 to 100 mOhms - squeeze test.png
    USB cables on Y-axis zoom 2 are stable and predictable with the Forest showing a little more disturbance than the others. Pyst is a great compromise between stability and price. Carbon shows the least disturbance but is also the priciest of those tested in Part II.
     
    Last edited: Feb 6, 2018
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  5. atomicbob

    atomicbob dScope Yoda

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    Here are the Benchvue raw measurements for the 10 minute data acquisitions.

    Please note Benchvue y-axis changes for each measurement to maximize data displayed. What appears to be a large change may be quite small relative to another USB cable raw measurement. Pay attention to y-axis values.


    01 generic clear small shield - 75 cm
    01 20180205-1955 generic clear small shield R.png

    05 Audioquest Forest shield - 75 cm
    05 20180205-1820 Audioquest Forest shield R - 75cm.png

    08 Schiit Pyst shield - 100 cm
    08 20180205-1555 Pyst shield R.png

    09 Schiit Pyst shield - second sample - 100 cm
    09 20180205-1635 Pyst 2 shield R.png

    10 Audioquest Pearl shield - 150 cm
    10 20180205-1840 Audioquest Pearl shield R - 150cm.png

    11 Audioquest Carbon shield - 75 cm
    11 20180205-1910 Audioquest Carbon shield R - 75cm.png

    12 Wireworld Ultraviolet 7 shield - 75 cm
    12 20180205-1930 Wireworld Ultraviolet 7 shield R - 100cm.png

    13 Monoprice shield - 100 cm
    13 20180205-1705 013 Monoprice shield R.png
     
    Last edited: Feb 6, 2018
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  6. atomicbob

    atomicbob dScope Yoda

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    reserved for Part II 3/3.

    Part II 3/3 will be LCR meter capacitance frequency sweeps when the BK Precision 891 arrives next month.
     
    Last edited: Feb 7, 2018
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