[SI-LIST] Re: PVC material and dielectric loss
- From: "Howard Johnson" <howie03@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 18 Aug 2009 08:32:56 -0700
Dear Neo,
Your original message asked about "PVC" insulated cables. A good example
would be the widely-installed category-3 unshielded twisted pair (UTP) cable
specified for use in (among other things) Ethernet 10BASE-T installations.
In the four-pair form with 24-gauge conductors this is what many people
think of as "telephone wire". Many inexpensive multi-conductor cables still
use PVC insulation. The dielectric loss tangent of category-3 UTP is about
0.016 at 10 MHz; not that different from worst-case FR-4 (ref: "High-Speed
Digital Design: More Black Magic, p. 463). With this cable at 10 MHz you
can expect about 6-7 dB/100m of resistive loss plus an additional 4 dB/100m
of dielectric loss.
In the world of Ethernet, the category-3 cable was superceeded for new
installations in 1995 by a new cable, called category-5, that uses a lower
dielectric loss teflon-like insulation (PTFE is the chemical name -- if I
remember correctly). That material has a dielectric loss tangent at 10MHz of
about 0.00115 (ibid). By the way, the materials properties and dielectric
loss tangents are not specified as part of the cable spec; only the overall
loss number. What I am telling you is the "typical" construction of cables
that meet these twisted-pair standards. For category-5 UTP at frequencies
up to 65 MHz and beyond the predominate loss mechanism is resistive loss.
Mr. Egan points out that many high-speed cables use polyethelene insulation.
In my experience that is certainly true for coaxial cables. The polyethelene
material is particularly nice because it can be "foamed", a process that
forms millions of tiny bubbles of gas within the plastic insulation,
lowering its density, and thereby further improving (lowering) the
dielectric loss.
Best regards,
Dr. Howard Johnson, Signal Consulting Inc.,
tel +1 509-997-0505, howie03@xxxxxxxxxx
www.sigcon.com -- High-Speed Digital Design seminars, publications and films
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Neo
Sent: Tuesday, August 18, 2009 8:00 AM
To: 'List Si'; Kenneth W. Egan
Subject: [SI-LIST] Re: PVC material and dielectric loss
Hi,
Thanks for the reply and help.
Polyolefin's loss tangent is 3e-4 while FR4 is 8e-3.
I think cable should be way better than FR4 in dielectric loss. Right?
Regards,
Neo
--- On Tue, 8/18/09, Kenneth W. Egan <kegan@xxxxxxxxxxxxx> wrote:
From: Kenneth W. Egan <kegan@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: PVC material and dielectric loss
To: "'Neo'" <neoflash2008@xxxxxxxxx>, "'List Si'" <si-list@xxxxxxxxxxxxx>
Date: Tuesday, August 18, 2009, 4:12 AM
Most high speed cables use polyoelifin, i.e. polyethylene. Some are foamed
to create a lower effective Er.
Nope. Dielectric loss dominates ( depending on bitrate / frequency ).
KWE
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Neo
Sent: Monday, August 17, 2009 10:34 PM
To: List Si
Subject: [SI-LIST] PVC material and dielectric loss
Hi,
I read from material that most cables are using PVC as insulator material.
And I checked its loss tangent and found there is even no data for it (maybe
it is too small).
Does this mean that PVC cable suffers mostly copper loss, and complete
immune to dielectric loss?
Regards,Neo
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
