Length of USB cable w/o twisted data pair to reach Hi Speed 480Mbps

[berkeman]

Just out of random curiosity? Pick a cable at random, a connector at random and a protocol at random? I don't believe it.

You don't have to provide context, but if you make us guess, you are going to get worse advice. Or, as Barbara Billingsley once said...

I just want to know if the china Lemo clones especially the 4 pin can also work in 480Mbps.

Lemo connectors are for audio, not half-GHz RF. This thread of yours has gone on long enough, and is now closed.

 

[berkeman]

UPDATE -- I missed this helpful post by @f95toli and I did not realize that there were special versions of LEMO connectors that were designed for RF:

That said, Lemo has in recent years designed some inserts to be used specifically with USB and ethernet.
https://web.lemo.com/img/resources/catalog/ROW/UK_English/High_speed_data_transfer.pdf

Hence, as long as you are using that specific model with the right type of cable you should be OK.

Thread is reopened provisionally.

I just want to know if the china Lemo clones especially the 4 pin can also work in 480Mbps. f95toli. I looked at your hi-speed catalog. Does it mean all 4 pin LEMO series are automatically hi-speed? because I can't see the difference in the model between ordinary and hi-speed.

Unless you use a connector that is specifically designed to maintain an RF $Z_0$ (characteristic impedance) all along the signal propagation path from cable through the connector(s), there will be reflections that will cause jitter in the receive waveform and "close the eye diagram", which can result in data errors. This includes how the wiring/cabling is handled once you get through the RF LEMO connectors in into the enclosure that you have shown in another picture. You would need to control the $Z_0$ of the interconnect inside the box as well, all the way to the USB IC that is receiving the signals.

And your comments about a DC device actually using AC signalling on USB are a bit baffling to me. You do understand how the 480Mbps signalling works on USB 2.0, right? (lower speed example shown below from Wikipedia)

https://en.wikipedia.org/wiki/USB_communications

 

[Averagesupernova]

And your comments about a DC device actually using AC signalling on USB are a bit baffling to me.

The reason for my post. In way over his head at that point. Have not had a reply on that. I meant it in a constructive manner.

 

[berkeman]

The reason for my post. In way over his head at that point. Have not had a reply on that. I meant it in a constructive manner.

Yeah, it makes me wonder why we are trying to give detailed $Z_0$ transmission line advice when they ask this:

No. I just wondered how an equipment that was completely powered by DC can produce AC signal at the USB port.. I guess it's the USB chips that can do that.

...but I guess we all have to start learning somewhere...

 

[Ephant]

Ok last request, let's compute it because in another electronics group, people are convinced all LEMO connectors can do USB 2.0 or 480Mbps. Theys said for example:

"You would have to make a catastrophically bad connector to fail to work for usb 2.0. A bad cable maybe but the connector is just too small and absent deliberate inductors in the signal path or failing to connect a wire altogether its going to work."

I showed f95toli document and one commented:

"I saw that document long ago. It’s just their recommendations. As far as I can tell, they aren’t special insert configurations, at least not for USB 2, they’re just their standard 4-pin inserts in the recommended sizes, with a recommended pinout. They probably calculated which of their existing inserts works best for USB 2 and recommend that connector size. Because if you look at their overall catalog, “304” is one of their standard insert sizes, with no mention of USB 2. I think they list that on some SKUs simply as a convenience."

"Note that in that datasheet, when they say “proprietary interface” as the insert type, they mean “LEMO design, not an open standard”, NOT that it was designed specifically for USB!".

Ok. Let's compute it. Why can't ordinary LEMO connectors survive 480Mbps?? In original USB male plug, is it impedance matched to the twisted wires? Please show computations as one last request. Thank you..

 

[f95toli]

Ok. Let's compute it. Why can't ordinary LEMO connectors survive 480Mbps?? In original USB male plug, is it impedance matched to the twisted wires?

Because most likely that won't result in the right impedance. The impedance when you use a specific connector will depend on the geometry (distance between pins etc) of the connector itself, the dielectric constant of the materials used, how the shield of the cable it attached, in what order the wires are attached etc....There are lots of factors; and even very small differences will result in changes in the impedance; and if the impedance if wrong the signal coming through the cable will be reflected.

There is absolutely no way to calculate this analytically and get even close; simulations of this type are always done using EM simulation software (although a generic FEM solver like COMSOL might also work ).

It is entirely true -as is you were told- that there is nothing "special" about the LEMO connector sold for USB 2.0. But the point is that that particular type happens to have geometry that result in in the right impedance; this obviously does not mean that ALL Lemo connectors will work since Lemo makes connectors of many different sizes and with different pin configurations .

if you want to have a "well document" example of this just compare SMA connectors of different impedance; the 75 ohm and 50 ohms versions look very similar (and I think you they even fit together if you use some force, NOT recommended); however the impedance differs by 50% due to small differences in things like the diameter of the inner pins. If you try to use a 75 ohm connector in a 50ohm environment it will work fine at low frequencies; but at higher frequencies you will get lots of reflections.

 

[Ephant]

Because most likely that won't result in the right impedance. The impedance when you use a specific connector will depend on the geometry (distance between pins etc) of the connector itself, the dielectric constant of the materials used, how the shield of the cable it attached, in what order the wires are attached etc....There are lots of factors; and even very small differences will result in changes in the impedance; and if the impedance if wrong the signal coming through the cable will be reflected.

There is absolutely no way to calculate this analytically and get even close; simulations of this type are always done using EM simulation software (although a generic FEM solver like COMSOL might also work ).

It is entirely true -as is you were told- that there is nothing "special" about the LEMO connector sold for USB 2.0. But the point is that that particular type happens to have geometry that result in in the right impedance; this obviously does not mean that ALL Lemo connectors will work since Lemo makes connectors of many different sizes and with different pin configurations .

if you want to have a "well document" example of this just compare SMA connectors of different impedance; the 75 ohm and 50 ohms versions look very similar (and I think you they even fit together if you use some force, NOT recommended); however the impedance differs by 50% due to small differences in things like the diameter of the inner pins. If you try to use a 75 ohm connector in a 50ohm environment it will work fine at low frequencies; but at higher frequencies you will get lots of reflections.

How about the USB 3.1 with 5Gbps vs 480Mps or 10X more. Does the original Lemo connectors matching the 9 pin also happened to have the same or very similar impedances? If so, then it may be easy to match impedances between wires and connectors, is it not, because in the case of the Lemo USB 3.1. It matches coincidentally too.

 

[Vanadium 50]

How about the USB 3.1

What do you think?

You've been given dozens of messages on how things work in general. What have you learned, and how do you think it applies here?

 

[Ephant]

I learnt wavelength of 480Mbps is 0.62 meter versus 0.06 meter for that of 5 Gbps. I assume 5 Gbps is same as 5Gigahertz (?)

if the wavelength is much shorter, the tolerance in the connector must even be more exact (?) I learnt impedance in the connector is related to the geometry (distance between pins etc) of the connector itself, the dielectric constant of the materials used, how the shield of the cable it attached, in what order the wires are attached etc.

Since the impedance of both USB 2.0 and USB 3.1 are both 90 Ohms. How could the connectors of 9 pins versus 4 pins be similar in impedance, and coincidentally? Unless Lemo designed the 9 pin impedance of the connector on purpose. And if they do, then they could also have redesigned the impedance of the 4 pin (?)

Let's wait for f95toli computations of 480Mbps versus 5 Gbps tolerance and see if both connectors can still coincidentally match it without any modifications. Also I watched a lot of youtube about impedance mismatch.

Without capacitance and inductance to cause impedance and impedance mismatch. Why would it violate Einstein Theory of Relativity which states that information can never travel faster than the speed of lights?
That guy is everywhere, even on wires.