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Science Forum Index » Electronics - Components Forum » Why do some USB leads have a "blob" on them?
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| Jon D |
 Posted: Wed Feb 07, 2007 12:47 pm |
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Why do some of my USB leads (for example those which came with my
dictation machine) have a largish cylindrical plastic "blob" on them?
The blob is about an inch long and half an inch is diameter. |
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| Palindrome |
| Posted: Wed Feb 07, 2007 1:07 pm |
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Jon D wrote:
Quote: Why do some of my USB leads (for example those which came with my
dictation machine) have a largish cylindrical plastic "blob" on them?
The blob is about an inch long and half an inch is diameter.
They are ferrite cores. Do a Google search on "ferrite cores for
interference suppression", eg:
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13975
--
Sue |
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| Don Bruder |
| Posted: Wed Feb 07, 2007 1:17 pm |
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Guest
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In article <Xns98D0AAD2F104217E53A@127.0.0.1>, Jon D <jon@nomail.com>
wrote:
Quote: Why do some of my USB leads (for example those which came with my
dictation machine) have a largish cylindrical plastic "blob" on them?
The blob is about an inch long and half an inch is diameter.
It's usually called a "ferrite" or "toroid", and it's there to keep
radio frequency noise from being generated/transmitted by the device.
Digital data on wires is usually *VERY* "noisy" from a radio viewpoint,
and the noise often gets worse as the data speed on the wires increases.
At USB speeds, it's possible, if you've got a poorly designed cable or
piece of hardware, to completely wipe out nearby radio reception.
If you were to open one up, you'd find that it's usually a black "donut"
of material (A soft form of iron, called, appropriately enough,
"ferrite") with the wires that make up the cable wrapped through the
center, sometimes as a bundle, sometimes each wire individually, then
the whole thing is wrapped in a protective plastic cover.
--
Don Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist,
or the subject of the message doesn't contain the exact text "PopperAndShadow"
somewhere, any message sent to this address will go in the garbage without my
ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info |
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| Guest |
| Posted: Wed Feb 07, 2007 1:27 pm |
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On Wed, 07 Feb 2007 16:47:33 GMT, Jon D <jon@nomail.com> wrote:
Quote: Why do some of my USB leads (for example those which came with my
dictation machine) have a largish cylindrical plastic "blob" on them?
The blob is about an inch long and half an inch is diameter.
That is a ferrite bead to block some of the common mode noise you
might get. |
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| Rod Speed |
| Posted: Wed Feb 07, 2007 3:11 pm |
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gfretwell@aol.com wrote:
Quote: On Wed, 07 Feb 2007 16:47:33 GMT, Jon D <jon@nomail.com> wrote:
Why do some of my USB leads (for example those which came with my
dictation machine) have a largish cylindrical plastic "blob" on them?
The blob is about an inch long and half an inch is diameter.
That is a ferrite bead to block some of the common mode noise you might get.
Nope, its to stop the cable radiating. |
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| Michael C |
| Posted: Wed Feb 07, 2007 9:49 pm |
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"Jon D" <jon@nomail.com> wrote in message
news:Xns98D0AAD2F104217E53A@127.0.0.1...
Quote: Why do some of my USB leads (for example those which came with my
dictation machine) have a largish cylindrical plastic "blob" on them?
The blob is about an inch long and half an inch is diameter.
What I'm interested to know is why do some usb devices have them while
others survive quite well without. |
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| Dave Platt |
| Posted: Wed Feb 07, 2007 10:07 pm |
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In article <45ca8207$0$21086$afc38c87@news.optusnet.com.au>,
Michael C <nospam@nospam.com> wrote:
Quote: What I'm interested to know is why do some usb devices have them while
others survive quite well without.
The tendency of an electronic device to radiate unwanted
radio-frequency energy depends on a number of things, including the
frequency of the internal clock circuitry, the power consumption, the
PC board layout, the type of case (metal or plastic) and case
shielding, the presence or absence of internal RF-blocking components
(e.g. small ferrite beads or bypass capacitors), and probably at least
a dozen other factors.
Here in the US, the FCC sets limits for how much energy an incidental
radiator (e.g. a computer or component thereof) is allowed to emit.
In principle, each USB device design is supposed to be tested in a
third-party lab, and "certificated" (i.e. shown via testing) to comply
with the limits.
So... some USB devices might not need any extra RF blocking on their
cables, because their design is inherently a low-speed, low-RF-
emitting one. Or, they might not need it becauset the manufacturer
put the necessary RF blocking/shielding into the USB device design
itself (e.g. a metal case, ferrite beads on the PC board wiring, use
of a spread-spectrum oscillator to reduce individual emission spurs,
etc.). Or, the manufacturer might be cheating... i.e. certificated
one version of the device (with a ferrite-bead cable) and then
switched to a less expensive cable design for actual production and
sale.
If you're curious, take a look at the bottom/back of your USB device,
and find the FCC Part 15 information. You can plug this information
into the form at
https://gullfoss2.fcc.gov/prod/oet/cf/eas/reports/GenericSearch.cfm
and access the reports which were filed when the device was
certificated.
If you've got a USB device which has no Part 15 certification label,
it may be an untested/unauthorized device, and thus potentially
illegal to sell here in the U.S.
--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads! |
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| MassiveProng |
| Posted: Wed Feb 07, 2007 10:18 pm |
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On Wed, 07 Feb 2007 16:47:33 GMT, Jon D <jon@nomail.com> Gave us:
Quote: Why do some of my USB leads (for example those which came with my
dictation machine) have a largish cylindrical plastic "blob" on them?
The blob is about an inch long and half an inch is diameter.
Maybe if you knew what the blob was, and what it is called, you
wouldn't have to ask.
It is an RF and EM emissions filter. |
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| Homer J Simpson |
| Posted: Wed Feb 07, 2007 10:23 pm |
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"Michael C" <nospam@nospam.com> wrote in message
news:45ca8207$0$21086$afc38c87@news.optusnet.com.au...
Quote: What I'm interested to know is why do some usb devices have them while
others survive quite well without.
The Chinese don't care. The US companies will use them as needed to comply
with FCC rules. |
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| Eeyore |
| Posted: Thu Feb 08, 2007 1:59 am |
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Michael C wrote:
Quote: "Jon D" <jon@nomail.com> wrote in message
Why do some of my USB leads (for example those which came with my
dictation machine) have a largish cylindrical plastic "blob" on them?
The blob is about an inch long and half an inch is diameter.
What I'm interested to know is why do some usb devices have them while
others survive quite well without.
It's usually an add-on fix to reduce emissions to a level that'll pass
compliance testing. Since it'll cost more to use one than no doughnut - no-one
really *wants* to have to use them.
Graham |
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| Eeyore |
| Posted: Thu Feb 08, 2007 2:00 am |
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Homer J Simpson wrote:
Quote: "Michael C" <nospam@nospam.com> wrote in message
What I'm interested to know is why do some usb devices have them while
others survive quite well without.
The Chinese don't care.
The Chinese now have to meet IEC regs actually.
Graham |
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| Lostgallifreyan |
| Posted: Thu Feb 08, 2007 9:39 am |
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MassiveProng <MassiveProng@thebarattheendoftheuniverse.org> wrote in
news:t12ls2po2503738g7780u1eq980s6evof1@4ax.com:
Quote: Maybe if you knew what the blob was, and what it is called, you
wouldn't have to ask.
It is an RF and EM emissions filter.
He didn't know, so he asked. Problem? I think not. And you just compounded
your own 'cleverness' by answering with a minimal answer that has already
been said about TEN times before you showered us with your 'wisdom'. Did
you think you saw stupidity, or were you just staring into a mirror by
mistake? |
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| MassiveProng |
| Posted: Thu Feb 08, 2007 10:00 pm |
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On Thu, 08 Feb 2007 13:39:55 GMT, Lostgallifreyan <no-one@nowhere.net>
Gave us:
Quote: MassiveProng <MassiveProng@thebarattheendoftheuniverse.org> wrote in
news:t12ls2po2503738g7780u1eq980s6evof1@4ax.com:
Maybe if you knew what the blob was, and what it is called, you
wouldn't have to ask.
It is an RF and EM emissions filter.
He didn't know, so he asked. Problem? I think not. And you just compounded
your own 'cleverness' by answering with a minimal answer that has already
been said about TEN times before you showered us with your 'wisdom'. Did
you think you saw stupidity, or were you just staring into a mirror by
mistake?
Do you see anywhere where I wrote "stupid", you stupid motherfucker?
For the device that it is, the answer was fine. For the lay person
that was given the answer, the answer was fine. Ther was no need for
a detailed response about fucking ferrite EMI traps.
Grow the fuck up, you are a piss poor judge of anything social, and
apparently not too good on the technical side either. |
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| Lostgallifreyan |
| Posted: Thu Feb 08, 2007 10:10 pm |
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MassiveProng <MassiveProng@thebarattheendoftheuniverse.org> wrote in
news:68lns2hhv6ioe4mhken6j4p8s8piqnuoho@4ax.com:
Quote: On Thu, 08 Feb 2007 13:39:55 GMT, Lostgallifreyan <no-one@nowhere.net
Gave us:
MassiveProng <MassiveProng@thebarattheendoftheuniverse.org> wrote in
news:t12ls2po2503738g7780u1eq980s6evof1@4ax.com:
Maybe if you knew what the blob was, and what it is called, you
wouldn't have to ask.
It is an RF and EM emissions filter.
He didn't know, so he asked. Problem? I think not. And you just
compounded your own 'cleverness' by answering with a minimal answer
that has already been said about TEN times before you showered us with
your 'wisdom'. Did you think you saw stupidity, or were you just
staring into a mirror by mistake?
Do you see anywhere where I wrote "stupid", you stupid motherfucker?
For the device that it is, the answer was fine. For the lay person
that was given the answer, the answer was fine. Ther was no need for
a detailed response about fucking ferrite EMI traps.
Grow the fuck up, you are a piss poor judge of anything social, and
apparently not too good on the technical side either.
You are SO easily rattled. Funny. You thought that would hurt? I wouldn't
have called out your too-little too-late cleverness if I was worried about
that. While we have our silly little side-show, I imaging the OP is busy
with the sensible answers already given. You might igmore them, but anyone
else can see that the subject is already answered. People often put their
bit in as extra but they usually try to add something instead of trying to
make the OP look like a plonker for asking a simple and sensible question. |
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| MassiveProng |
| Posted: Thu Feb 08, 2007 10:13 pm |
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On Fri, 09 Feb 2007 02:10:23 GMT, Lostgallifreyan <no-one@nowhere.net>
Gave us:
Quote: MassiveProng <MassiveProng@thebarattheendoftheuniverse.org> wrote in
news:68lns2hhv6ioe4mhken6j4p8s8piqnuoho@4ax.com:
On Thu, 08 Feb 2007 13:39:55 GMT, Lostgallifreyan <no-one@nowhere.net
Gave us:
MassiveProng <MassiveProng@thebarattheendoftheuniverse.org> wrote in
news:t12ls2po2503738g7780u1eq980s6evof1@4ax.com:
Maybe if you knew what the blob was, and what it is called, you
wouldn't have to ask.
It is an RF and EM emissions filter.
He didn't know, so he asked. Problem? I think not. And you just
compounded your own 'cleverness' by answering with a minimal answer
that has already been said about TEN times before you showered us with
your 'wisdom'. Did you think you saw stupidity, or were you just
staring into a mirror by mistake?
Do you see anywhere where I wrote "stupid", you stupid motherfucker?
For the device that it is, the answer was fine. For the lay person
that was given the answer, the answer was fine. Ther was no need for
a detailed response about fucking ferrite EMI traps.
Grow the fuck up, you are a piss poor judge of anything social, and
apparently not too good on the technical side either.
You are SO easily rattled. Funny. You thought that would hurt? I wouldn't
have called out your too-little too-late cleverness if I was worried about
that. While we have our silly little side-show, I imaging the OP is busy
with the sensible answers already given. You might igmore them, but anyone
else can see that the subject is already answered. People often put their
bit in as extra but they usually try to add something instead of trying to
make the OP look like a plonker for asking a simple and sensible question.
This is an engineering group, dipshit. That question belongs in a
basic electronics group, at best.
I read the OP and didn't read, nor did I need to read ANY of the
other responses to make my own.
So again, jackass... fuck off, and NO I am not angry, I am fucking
laughing at your retarded ass. |
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