What's that dongle in the USB cable? Is it important?

On the short USB cable that came with my Clip+ there is a small dongle in the middle, closer to the mini usb plug end. Is that a fuse? Is it important? I’ve noticed a lot of people saying they’ve used any old random other USB cable with no problem on the Sansa Clips. But it does seem atypical of a USB cable to have a dongle/fuse in the middle like that. Also, if I use this cable with other devices (like my phone), so I only have to carry one cable around, will the dongle/fuse effect it? Thanks.

Fine to use other USB cables with the Clip; fine to use the supplied USB cable with other devices.  The dongle is supposed to help keep the signals clean.  Here’s some information I found; others likely will have other info.

Ferrite cores are used around cables for Electromagnetic Interference (EMI)
suppression. They reduce the extraneous currents in the cables produced by
large, nearby Radio Frequency fields such as AM radio transmitters, TV
transmitters, amateur radios, shipboard radios, etc. These currents, while
not usually strong enough to cause damage, can upset sensitive circuits in
computer or peripherals and cause data errors. Use of such cores will have
no effect on transfer of the desired data from the camera to the computer
via the Universal Serial Bus (USB).

The ferrite core seems to be quite common in USB cables with mini connectors, actually. I have a number of mini-USB cables that came with different devices (Clip, phone, camera, video capture doohickey, etc.) and they all have ferrite cores. I don’t recall ever seeing one in a cable with full-sized connectors, though.

@gwk1967 wrote:

The ferrite core seems to be quite common in USB cables with mini connectors, actually. I have a number of mini-USB cables that came with different devices (Clip, phone, camera, video capture doohickey, etc.) and they all have ferrite cores. I don’t recall ever seeing one in a cable with full-sized connectors, though.

They’re more common than you’d think.  Iomega used to include cables with the ferrite cores and full-sized “B” connectors with many of their USB Zip drives and external hard drives.  I have 3 or 4 of them.

The Clip cable includes a ferrite RFI trap, quite useful especially when using a short cable run, as the under-10-inch cable is indeed short.

The digital information travelling across that cable is protected against interference, as shown:

Let ±λ be the charge per unit length of each line charge without relativistic contraction, i.e., in the frame moving with that line charge. Using the approximation γ=(1-_v_2/_c_2)-1/2≈ 1+_v_2/2_c_2 for v<< c, the total charge per unit length in frame 2 is

Let R be the distance from the line charge to the lone charge. Applying Gauss’ law to a cylinder of radius R centered on the line charge, we find that the magnitude of the electric field experienced by the lone charge in frame 2 is

E = frac{4klambda uv}{c^2R} qquad ,

and the force acting on the lone charge q is

F = frac{4klambda quv}{c^2R} qquad .

In frame 1, the current is I=2λ1 u (see homework problem 5), which we can approximate as I=2λ u, since the current, unlike λ_total_, 2, doesn’t vanish completely without the relativistic effect. The magnetic force on the lone charge q due to the current I is

F = frac{2kI qv}{c^2R} qquad .

Well, okay, let’s simplify:

As shown, the tin foil hat prevents stray electromagnetic fields from affecting the wearer’s mind.  Conversely, the tin foil hat protects us from the stray electromagnetic emissions of the hat wearer’s mind as well.

Bob  :stuck_out_tongue:

Message Edited by neutron_bob on 10-26-2009 11:32 AM

Thanks for the responses. Including the brilliant mathematical proof, which I’ll have to go back to school to understand, and equally brilliant tin foil hat executive summary.

Message Edited by cb474 on 10-24-2009 12:35 AM

Thanks for the responses. Including the brilliant mathematical proof, which I’ll have to go back to school to understand, and the genuinely inspired tin foil hat executive summary.

@neutron_bob wrote:

 

Well, okay, let’s simplify:

 

 

As shown, the tin foil hat prevents stray electromagnatic fields from affecting the wearer’s mind.  Conversely, the tin foil hat protects us from the stray electromagnetic emissions of the hat wearer’s mind as well.

 

 

Bob  :stuck_out_tongue:

LOL.  From the expression on the cat’s face, I’d say that the cat is thinking “Why me?”  Wouldn’t this be considered one step short of animal abuse? :stuck_out_tongue:

Indeed, that cat looks like he’s about ready to blow, doesn’t he?  Check out the eyes.

Bob  :dizzy_face: