4 ms·

As always, these testers (the affordable ones) are capable of testing continuity, and, I guess, the cable chip report. If you want to test bandwidth, that's a

As always, these testers (the affordable ones) are capable of testing continuity, and, I guess, the cable chip report. If you want to test bandwidth, that's a five- or six-figure bit of gear.

nerdsniper 3mo ago
This keeps needing to be pointed out every thread this appears on. Plenty of cables have eMarkers that claim "40Gbps" or whatever speeds, or support 240W PD...but absolutely cannot deliver either of those. And none of these consumer level testers can test either of those claims. Resistance measurements can cursorily test claims of 240W but resistance changes with temperature which changes with current...so unless your tester puts 5 amps down the wire for 5 minutes and then tests resistance it's not a very good test.
- maya335 3mo ago
  Yeah — "the eMarker said 40Gbps" is basically the same problem as trusting the print on the jacket. For home use I've ended up treating real capability as an empirical property of the specific cable+port+device combo: does this exact cable drive this monitor at the mode I want, under load, for an hour? If yes, it gets a colored heat-shrink band and never leaves that use case. Everything else is a phone/charge cable until proven otherwise.
  - ChrisMarshallNY 3mo ago
    That’s a very practical approach.
- consp 3mo ago
  I had a cheap no-name cable which claims 3.1 speeds (and thus needs a marker), though it lacks all differential pairs and borks every usb connection (after I cut it, it was obvious). No clue why it contains a marker chip but doesn't have any conductors. Likely for usb-pd but you do not want to put any power though it anyway as the conductors were cheap copper clad aluminium.
Gigachad 3mo ago
It’s much cheaper to just buy your cables from Apple or LTT knowing they tested them on a 6 figure testing rig. I throw out every usb cable that comes bundled with devices because they are literal junk.
- ErneX 3mo ago
  I use the ones provided by Apple and it’s been pretty good so far.
mshroyer 3mo ago
Why on earth is so much more expensive than an arbitrary pair of devices that could max out a cable?
- ChrisMarshallNY 3mo ago
  Think about it. You need to generate a precise, calibrated, 40GHz signal, transmit it, then precisely measure the returned signal for phase, amplitude, and waveform integrity -at that speed. Oscilloscopes and logic analyzers that run at that speed, are damn expensive.
  - CamperBob2 3mo ago
    Someone could do an equivalent-time sampling instrument for not much money, if the market were there. It's probably not, though.
    - ChrisMarshallNY 3mo ago
      Time sampling isn’t enough. You need to at least look at waveform integrity (which can be approximated, by doing things like looking for harmonics). For example, you may send in a 40 GHz square wave, and get back a wave full of ringing, or a sine or sawtooth wave. It’s damn difficult to maintain clean square waves, at that frequency. The cable could also double as a microwave antenna. Since it’s digital information, some waveform alterations are OK, but not too much. You need fairly clear state transitions. Ringing, or waveform distortion, can introduce extra (or fewer) transitions; thus, completely changing the data.
      - CamperBob2 3mo ago
        That's not really what I mean. You don't have to diagnose the signal, just the medium, which can tell you what will happen to the real signal. It requires a fast edge (or a very broadband sweep), but nothing much beyond that. E.g., here's what a bad connector at the far end of an SFF-8654 cable looks like on a TDR: https://i.imgur.com/AiLnSuC.jpeg https://i.imgur.com/AiLnSuC.jpeg . This type of plot can be interpreted as impedance versus distance along the line. It could be made with a small handheld instrument, but currently a human is needed to read the tea leaves. While I was making that measurement, I couldn't help thinking that it would be nice if it didn't require either a 50 GHz VNA or equally-expensive training to read. Equivalent-time sampling gets you out of needing an expensive network analyzer, but it doesn't help with the diagnosis itself. And of course when checking a USB cable you are most likely just after a go/no-go result, not the gory details. That further calls the market economics of such a gadget into question. Still, if somebody offered one at a reasonable price, they'd sell at least one to me.
deleted 3mo ago
[deleted]

As always, these testers (the affordable ones) are capable of testing continuity, and, I guess, the cable chip report. If you want to test bandwidth, that's a five- or six-figure bit of gear.

nerdsniper 3mo ago

This keeps needing to be pointed out every thread this appears on. Plenty of cables have eMarkers that claim "40Gbps" or whatever speeds, or support 240W PD...but absolutely cannot deliver either of those. And none of these consumer level testers can test either of those claims. Resistance measurements can cursorily test claims of 240W but resistance changes with temperature which changes with current...so unless your tester puts 5 amps down the wire for 5 minutes and then tests resistance it's not a very good test.

maya335 3mo ago
Yeah — "the eMarker said 40Gbps" is basically the same problem as trusting the print on the jacket. For home use I've ended up treating real capability as an empirical property of the specific cable+port+device combo: does this exact cable drive this monitor at the mode I want, under load, for an hour? If yes, it gets a colored heat-shrink band and never leaves that use case. Everything else is a phone/charge cable until proven otherwise.
- ChrisMarshallNY 3mo ago
  That’s a very practical approach.
consp 3mo ago
I had a cheap no-name cable which claims 3.1 speeds (and thus needs a marker), though it lacks all differential pairs and borks every usb connection (after I cut it, it was obvious). No clue why it contains a marker chip but doesn't have any conductors. Likely for usb-pd but you do not want to put any power though it anyway as the conductors were cheap copper clad aluminium.

Gigachad 3mo ago

It’s much cheaper to just buy your cables from Apple or LTT knowing they tested them on a 6 figure testing rig. I throw out every usb cable that comes bundled with devices because they are literal junk.

ErneX 3mo ago
I use the ones provided by Apple and it’s been pretty good so far.

mshroyer 3mo ago

Why on earth is so much more expensive than an arbitrary pair of devices that could max out a cable?

ChrisMarshallNY 3mo ago
Think about it. You need to generate a precise, calibrated, 40GHz signal, transmit it, then precisely measure the returned signal for phase, amplitude, and waveform integrity -at that speed. Oscilloscopes and logic analyzers that run at that speed, are damn expensive.
- CamperBob2 3mo ago
  Someone could do an equivalent-time sampling instrument for not much money, if the market were there. It's probably not, though.
  - ChrisMarshallNY 3mo ago
    Time sampling isn’t enough. You need to at least look at waveform integrity (which can be approximated, by doing things like looking for harmonics). For example, you may send in a 40 GHz square wave, and get back a wave full of ringing, or a sine or sawtooth wave. It’s damn difficult to maintain clean square waves, at that frequency. The cable could also double as a microwave antenna. Since it’s digital information, some waveform alterations are OK, but not too much. You need fairly clear state transitions. Ringing, or waveform distortion, can introduce extra (or fewer) transitions; thus, completely changing the data.
    - CamperBob2 3mo ago
      That's not really what I mean. You don't have to diagnose the signal, just the medium, which can tell you what will happen to the real signal. It requires a fast edge (or a very broadband sweep), but nothing much beyond that. E.g., here's what a bad connector at the far end of an SFF-8654 cable looks like on a TDR: https://i.imgur.com/AiLnSuC.jpeg https://i.imgur.com/AiLnSuC.jpeg . This type of plot can be interpreted as impedance versus distance along the line. It could be made with a small handheld instrument, but currently a human is needed to read the tea leaves. While I was making that measurement, I couldn't help thinking that it would be nice if it didn't require either a 50 GHz VNA or equally-expensive training to read. Equivalent-time sampling gets you out of needing an expensive network analyzer, but it doesn't help with the diagnosis itself. And of course when checking a USB cable you are most likely just after a go/no-go result, not the gory details. That further calls the market economics of such a gadget into question. Still, if somebody offered one at a reasonable price, they'd sell at least one to me.

deleted 3mo ago

[deleted]