USB CABLE "CYLINDER" SHAPE?

  Kibo Kid 03:53 20 Jan 03
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  Kibo Kid 03:53 20 Jan 03

I bought a Creative Labs Extigy sound card last month so that I can have decent sound from my notebook when I am abroad on assignments.

Unfortunately I left the cable connecting the Extigy unit to the notebook in the UK. The notebook end is USB , the Extigy end goes into a rectanglar port with angled corners (like Firewire?).

I have a similar cable connecting my external Iomega HDD to a PC Card USB 2.0 Port Adapter, but this one has a cyclinder shape just before the USB port.

What is the function of this cylinder? I see it on other cables, eh recharging cable for digital camera.

Can I not buy a Belkin cable with the correct ends, even if it does not have a cylinder? I cannot recall if the cable left behind in the UK has one.

Regards,

Kibo Kid

  -pops- 06:39 20 Jan 03

The cylinder is an electromagnetic choke designed to filter out (choke) high frequency currents which may interfere with the equipment the cable is connected to. The cable is looped around a ferrite core and in some types you can see the cable looped like this.In others it is hidden. This has become more important as processing speeds have increased.

You can very often use cables without the choke if necessary. I don't think any harm will occur. If you do get interference you can often move various bits around to minimise this.

Brian

  Gongoozler 09:20 20 Jan 03

-pops-, I don't think you are quite correct. The device is magnetic in function, but it is there as part of the emc (electromagnetic compatibility)compliance. The function is to prevent common mode high frequency from one piece of equipment getting to the other equipment. The way it works is like this. If there is a genuine high frequency signal, it will flow out of one wire (typically the signal wire) and return via another wire (typically a ground or signal negative). The result is that there is no net current (one cancels out the other), so the choke will have no effect. If, on the other hand, there is an earth difference, due perhaps to a noisy switch mode power supply in one of the pieces of equipment, then there may be a current in the earth wire from one equipment to the other. This current would not be cancelled out by a returning current in another wire - it may even be added to by a current in the same direction. In this case there would be a net current through the choke, and so the choke would attenuate it. These common mode chokes are very useful in that they significantly reduce common mode current while having no effect on the signal.

As -pops- says, if the cable without the choke works, you have nothing to worry about. If it is needed, then you may find that when you use your external hard drive. it interferes with some other equipment such as a radio receiver, or you may get some patterning on your computer display.

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