Connecting two USB cables together

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robroyzz

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Feb 9, 2007
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I have an external USB 80 GB HDD which connects to my pc's USB 2.0 port via a 3 ' standard USB 2.0 cable (A male to B male).

PC Af||Am---cable---Bm||Bf...HDD

Recently I moved the HDD and needed more than 3' to reach the pc. I had a USB Hub which has 1 B female connector and 4 A female connectors. I connected the pc via a 3' cable to the hub's B female connector and another 3' cable to one of the hub's A female connectors. The cable's B male plug connected to the HDD's B female connector and it works fine.

PC Af||Am---cable---Bm||Bf ..hub..Af||Am----cable----Bm||Bf...HDD

If I substitute a B female to A female adapter instead of the hub (the adapter is much cheaper than the hub) the pc tells me it can't recognize the device.

PC Af||Am---cable---Bm||Bf ..adapter..Af||Am----cable----Bm||Bf...HDD

The 4 port usb hub has a power input connector but I didn't need extra power for one port usage.

Can anyone tell me why it won't work?
It looks like all the pins (1 to 4) connect to the right pins in every connector pair.
What is different about the hub's Bf to Af connection?

Thanks
 
i would have bought a 6' cable instead of the adapter... but i don't really understand why it wouldn't work...

i'd probably test the continuity of the adapter... make sure they aren't crossed in there... or just a bad adapter....
 
It may be possible that the device does need the power.

Originally your were connect the device through a 3' cable. With an adapter, you're pushing the data over a 6' cable with a connector in between, and I'd guess that the connector doesn't really help the connection.

When you put it through the hub, the hub is powered and I would assume it's enhancing the signal rather than degrading it.
 
I would say that you need the power adapter for the device to recognize. Certain usb hubs are like this. or you can just go and get a 6' cable and be done with it.
 
One cable works.
The unpowered hub with 2 cables works fine. Not a length problem.
An adapter with the same 2 cables does not work.
Someone said that the standard usb cable has a crossover of data wires.
Two adapters with 3 cables does not work. If it was a crossover problem 3 cables would work as one.
Anyone know the wiring in a hub?
Thanks
 
I have overcome (not solved) the problem. I talked to a tech for a firm that sells adapters and hubs. He assured me that the adapter only has straight through connections from pin to pin. He also said usb connections can be fickle. Two cables with an adapter between should work between a device and a pc as long as the total length is no more than about 5 meters. But the adapter can present an interference/impedance/mismatch (connector to connector twice) and if not shielded can pick up some signal interference.
My initial try was 2 cables (A & B) and adapter between an external hard disk (EHDD) and a pc's usb port which only worked when I used a hub. Next, I tried 2 different cables (C & D) and adapter between my printer and pc and, to my surprise, it worked. I surmised that both cables and adapter were matched somehow. I then took one of these cables (C) and replaced the original adapter to pc cable (A) and (again to my surprise) it worked. Cable A was compatible with the hub (which also reconstructs the signal) but not the adapter.
When I used cable A, adapter and cable D with my printer to pc link it also worked.
I now have a link to the EHDD and another link to the printer and I can switch them (manually disconnect one cable and connect another) to either pc. I also demonstrated that "hot-switching" peripherals can work fine.

Thanks for all your help. I hope this explanation can also help any newbe that has usb cable problems.
 
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