firewire cable "loops"
 

I've recieved lots of cables here and there with one or both ends looped through a little plastic cylinder. I've never understood what this could possibly be used for and just opened the cylinders and threw them away. However, I just recieved a firewire 800 cable (with a Lacie harddrive) that was also looped through two large (1-inch diameter x 1-inch thick) metal cylinders. They're so heavy that I'm afraid the weight of the cable might damage the computer's firewire jack. So, before I go after these things with a hacksaw, does anyone have any idea what they're supposed to accomplish?

Sounds like you're talking about ferrite collars. I'm no expert, but my understanding is that they help shield the cables against radio frequency interference. I'm sure the engineers over at LaCie had a very good reason to put the collars on there, so you may want to see if you can live with the collars rather than cutting them off with a hacksaw.

Good luck.

Yep, they're ferrites. They are there to suppress RFI and EMI. Generally with computer stuff they are put there to suppress emissions - ie prevent the computer from interferring with other devices, and prevent cross talk between data channels. Some are mainly mainly there to comply with standard requirements.
In reality you could *maybe* remove them and not notice the difference but as mentioned, they are there for a reason and you may find you get quirky things happen if you do. Ferrites aren't cheap so they don't put them on just for fun.

Cheers,
Kyle.

Yes, the ferrites are there for a purpose, which is to prevent very high frequency signals from interferring with the main signals.

Some ferrites are removable, others are not.

You may be able to slide the cable so that the ferrite is not so close to the connector end. This may help with your weight concerns without significantly affecting the ferrites function.

If you do cut them off, you could purchase an add-on ferrite later. They have models that clamp over a cable instead of the cable being looped thru it.

Many firewire cables do not have ferrites, better quality cables do.

If you feel that you have to remove the ferrites, you may consider just breaking them. The ferrites are notoriously fragile.

Also, just remove one, not both of them if they are on both ends.

Thanks for the quick replies.
I guess I'm just a little confused at why they're so huge for a 4 foot cable (I'm used to seeing the smaller ones). I have three other firewire 800 cables that came with Lacie drives and they all have much smaller, typically sized ferrites. Are the larger ones possibly just an older design? Also, I have a few firewire 400 cables that are (from the factory as far as I can tell) identical except one has ferrites and the other two don't. Does that mean I should stick with the ferrite ones to avoid interference?

A well designed, well built cable, heavily shielded, can work very well without ferrites.

The Firewire 400 and 800 signals are digital.

I have used Firewire 400 cables with ferrites and I mainly use cables without ferrites. All of mine work equally well.

If you are worried about the extra weight, which I feel is a very legiminate concern, instead of removing the ferrites, why not just get another cable without the ferrites. They are not expensive.

I feel that you can successfully use the cables with ferrites and those without and you will never see a difference in the data transfer.