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Re: Can twisted wire replace shielded wire?

K

Keith Williams

Jan 1, 1970
0
As would be the resistance.
A zero-resistance (ideal) transmission line is just as realizable
as an infinite one.
 
R

RHF

Jan 1, 1970
0
DaviD - Speaking of "f*cked *p" . . .
Are 'you' Teaching the Master's Class ? :eek:)

DaviD - Considering "f*cking *p" . . .
It is practically impossible to do if you
'stick' with the Missionary Postion ! :eek:)

david - now go play with your radios ~ RHF
 
F

Fred Abse

Jan 1, 1970
0
So if all we have is a bare wire no current can flow?

You still have a dielectric - empty space (relative permittivity unity,
v = c = 3*10^8 meters/sec approximately). Characteristic impedance determined by
how far the wire is from ground (and a few other factors).

The value of v *in the conductor* is of little importance in determining
propagation velocity.

The concept of characteristic impedance and phase velocity was originally
developed with reference to telegraph lines which were single wires with
ground return.

A tube made of braided wires behaves like a solid tube if there is good
electrical contact at the wire crossings. The field is confined between
the inner conductor and the outer tube. The denser the braiding, the less
it leaks (ie. loses energy by radiation).

Now, a wire *helix* is a horse of a different color. That's how traveling
wave tubes work.
 
J

Jasen Betts

Jan 1, 1970
0
["Followup-To:" header set to sci.electronics.basics.]
Characteristic impedance and DC resistance are the same if the line is
infinitely long and unterminated.

if it was infinitely long wouldn't the
the termionation would make no difference for all proctical purposes.

wouldn't the resistance of the conductors throw that out ?
 
J

Jasen Betts

Jan 1, 1970
0
If you mean by "DC resistance", the impedance you would see at the input
of an infinitely long line, it's not bullshit, it's perfectly true, even
if the line is made of zero-resistance conductors. You'll just see the
line's characteristic impedance.

what about lines made of copper and plastic?

ISTM that a few hundered kilometers if RG59 is going to measure more
than 75 ohms even with far end is shorted.

There's no way an infinite length will have a lower resistance.

Bye.
Jasen
 
R

Robert Latest

Jan 1, 1970
0
["Followup-To:" header set to sci.electronics.design.]
On Mon, 28 Nov 2005 14:40:12 -0500,
in Msg. said:
A zero-resistance (ideal) transmission line is just as realizable
as an infinite one.

Superconductivity goes a pretty long way towards zero resistance. Wind a
superconducting transmission line once around the equator and make your
measurement on one end (leave the other end coming through your lab's
back door alone). Then you have roughly 1/4 second to establish your DC
resistance.

robert
 
J

Jasen Betts

Jan 1, 1970
0
So if all we have is a bare wire no current can flow?

noot sure what you mean:

1 > air is a dielectric (ie generally non-conductive)

2 > a solitary bare wire is an antenna, not a transmission line :)



Bye.
Jasen
 
C

Cliff

Jan 1, 1970
0
The value of v *in the conductor* is of little importance in determining
propagation velocity.

IOW The EM field in the dielectric can be several light-years away
(down the coax) from the electrons, protrons, anti-protons
or positrons in the coaxial conductor which it is related to?
No induced currents or voltages?
 
C

Cliff

Jan 1, 1970
0
Not at all. Since resistivity varies between conductors because of
the materials of which they're composed and inductance varies
because of their diameters, why would one _not_ expect c to vary?

You think that resistivity controls the speed of light?
I think I heard that a good vacuum has a lot of resistance
but a fairly high speed of light.
The speed of light goes down as things become more
conductive?
 
C

Cliff

Jan 1, 1970
0
david - now go play with your radios ~ RHF

CONTRACTOR'S STANDARD PIPE & FITTING SPECIFICATION
-------------------------------------------------------------------------------------------------

(1) All pipe is to be made of a long hole, surrounded by metal
concentric
with hole.

(2) All pipe is to be hollow throughout entire length. Do not use
holes
of different length than the pipe.

(3) All pipe is to be of very best quality, perfectly tubular or
pipular.

(4) All acid proof pipe is to be made of acid proof metal.

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the outside.

(6) All pipe is to be supplied with nothing in the hole so that
water, steam,
or other stuff can be put inside at a later date.

(7) All pipe is to be supplied without rust, as this can be more
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on at the job site.

(8) All pipe is to be cleaned free of any covering such as mud, tar,
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or any form of manure before putting up, otherwise it will make
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(9) All pipe over 500 feet long must have the words "long pipe"
clearly painted
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(10) Pipe over two miles long must also have these words painted in
the
middle so that fitter will not have to walk the full length of
pipe to
determine if it is long pipe or not.

(11) All pipe over six inches in diameter is to have the words "large
pipe"
painted on it, so that the fitter will not use it for small
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(12) All pipe closures are to be open on one end.

(13) All pipe fittings are to be made of the same stuff as the pipe.

(14) No fittings are to be put on pipe unless specified. If you do,
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becomes crooked pipe.

(15) Fittings come in all sort of sizes and shapes. Be sure to
specify the
direction you are going when ordering.

(16) Fittings come bolted, welded or screwed -- always use screwed.
They are
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(17) Flange must be used on all pipe. Flanges must have holes for
bolts
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(18) If flanges are to be blank or blind, the big hole in the middle
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(19) All flanges must be cast or forged of the very best iron metal,
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(20) Gaskets are to be used to fill spaces between flanges.

(21) Gaskets are to be made of metal, rubber, [plastic, paper or some
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(23) All bolts must have a head on one end and a nut on the other.

(24) Bolts without heads are to be furnished as studs.

(25) Studs without heads are to be screwed all over and have two nuts
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be odd.

(26) All nuts are to be furnished in sacks. Sacks must be whole and
sound,
minimum two nuts per sack. Paper sacks will not be tolerated.

(27) All piping must be installed with valves.

(28) All valves must have an opening on each end with a flapper in
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(30) Ball valves are not to be used anywhere with a female
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(31) Diaphragm valves are to be used with a female connection.

(32) All completed piping lines must go somewhere and connect to
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The fitter is required to verify this before turnover.

(33) All pipes shorter than 1/8" are uneconomical in use, requiring
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They are generally known as washers.

(34) Other commodities are often confused with pipes. These include:
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(35) Scottish Regiments in the Army use Army pipes in unusual ways.
These are
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(36) When ordering 90 degree or 30 degree elbows, be sure to specify
right hand or left hand, other wise you will be going the wrong
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(37) Be sure to specify to your vendor whether you want level, uphill
or
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(38) All coupling should have either right hand or left hand thread,
ut
do not mix the threads, otherwise, as the coupling is being
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(39) Joints in pipes for water must be water tight. Those in pipes
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(40) Lengths of pipe may we welded or soldered together. This method
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(41) Pipe over 5 feet in diameter shall have an arrow* painted at 10
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(42) When such pipe is longer than 20 feet all the arrows* must point
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* It has been suggested that the arrow(s) point to the open end
of the pipe.
This option is under study by the committee.
 
J

Joel Kolstad

Jan 1, 1970
0
Jasen Betts said:
2 > a solitary bare wire is an antenna, not a transmission line :)

In general I'd agree, although strictly speaking you can take something like
coax, flare out the shield into a horn, and just keep the inner conducting
going until you reverse the process on the other end. This ends up being sort
of an inside-out waveguide; I've read that it's been used successfully for
things like communications in mines or caves where it's cheaper and easier to
deploy (lighter) than traditional coax.
 
C

Cliff

Jan 1, 1970
0
noot sure what you mean:

1 > air is a dielectric (ie generally non-conductive)

2 > a solitary bare wire is an antenna, not a transmission line :)

I only have two 1.5 volt drycells .....
 
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