Re: Can twisted wire replace shielded wire?

[Cliff]

(snipped prior cutline)

Sure.

L
T = ---
R

That might seem to be a "time constant" ... but the velocity of
light is a vector with units ... are the units even correct?

No, as they become less vacuumy.

Provably explains why glass & plastics of various densities have
various indexes of refraction, right?
It's clearly a mass effect (gravity), right?

OOPs !! The less dense plastics can have a higher index of
refraction .... and, as light always seems to take the path of
*least time* ..... (BTW, How does it know in advance what
path that is?)

 

[[email protected]]

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

++++++++++++++++++++++
Have you ever heard of a G-line?

<http://www.broadcast.net/pipermail/radio-tech/2004-February/049867.html>

Or do a net search for G-line antenna way too many hits to list.

They really work. The loss is less then that of comparable ladder line
and way
less then 300 ohm ribbon or coax. Even though I have installed several,
I still
don't believe in them.

Terry

 

[Rich Grise]

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

If you have a feedhorn that has an impedance of 377 ohms at the open
end, it's called the "launcher", and your wire is a "G-line".

Cheers!
Rich

 

[Terry Given]

what about ferrite-loaded cables?!

oops. ya might wanna re-think that statement

here I was thinking the propagation velocity varied as 1/sqrt(Ur*Er)

where Ur and Er are the relative permeability and permittivity,
respectively.

Cheers
Terry

 

[Terry Given]

["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 ?

its hard to terminate infinitely long conductors, as finding the end can
be rather tricky

Cheers
Terry

 

[[email protected]]

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

+++++++++++++++++++++++++++
Ever heard of a G-line? ,AKA " Goubau Line".

See: <http://www.finitesite.com/wetnoodle/We0004.htm>
---------------------------------------------------------------------
"G-string or G-line: No this not something worn by an exotic dancer.
This is a form of rf transmission line. It was developed by Dr. Goubel.
Goubel was in the armed services when he came up with this. A G-line is
a true single wire transmission line system. For all practical
purposes, it is the inverse of a wave guide. With the wave guide the
signal travels through a pipe. With the G-line the signal the signal
travels around the outside of a single wire. Goubel went with the
concept that after a certain point the impedance of rf reaches a
maximum in free space. He devised a system for conversion of the
impedance from a coaxial cable to that of the the impedance of that
around a wire. Much like wave guide, the G-line has upper and lower
frequency limits. The major benefit of a G-line system is its
attenuation over a long run is much lower than other transmission line
system. Losses of 1db per mile at 200 MHz was not unheard of this
system. Is it in use anymore? I don't know. In the mid to late 1950's
it was common place. In the mid 1950's the FCC established the UHF tv
band. UHF stations started spring up all over. Somewhere around the
same time frame the FCC also allowed some VHF stations to be translated
into the UHF band. No tv was equipped with a UHF tuner initially. Many
companies made set top converter units. Nearly all of the early units
were hot carrier diode converters. They worked fine within 15 or 20
miles of a commercial UHF station. Where they fell short was on UHF
translators. Some of the earliest converters had a noise figure well in
excess of 12db, some were as much as 18 or 20db."
--------------------------------------------------------


There are many resfferences just do a net search for "g-line" antenna

The damn things really work]
Have lower loss then all but the best ladder line, way less loss
then good 300 Ohm. Of cousre they do leak some RF
whcih may be usefull.

Only for VHF and above.

And inspite of installing several g-line systems, I still don't
believe i them

Terry

 

[Fred Abse]

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?

Yes, electrons don't travel very fast at all. Nowhere near c.

 

[Fred Abse]

its hard to terminate infinitely long conductors, as finding the end can
be rather tricky

LOL!

 

[Fred Abse]

["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.
True


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

No

 

[Fred Abse]

what about lines made of copper and plastic?

Most are

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.

Run the LTSpice simulation below, three cases of 1000 miles of RG59-U,
terminated. shorted, and open at 1 MHz. You'll find all 3 cases look like
75 ohms. Constants are per Belden data.

LTSpice is free, if you didn't already know that, and runs under WINE,
(well at least here it does.)

RG59-U.asc

Version 4
SHEET 1 880 680
WIRE -128 144 -128 32
WIRE -128 160 -128 144
WIRE -128 320 -128 240
WIRE 48 320 -128 320
WIRE 48 320 48 64
WIRE 80 320 48 320
WIRE 80 320 80 176
WIRE 112 32 -128 32
WIRE 112 64 48 64
WIRE 112 144 -128 144
WIRE 112 176 80 176
WIRE 128 320 80 320
WIRE 128 352 128 320
WIRE 240 176 208 176
WIRE 240 320 128 320
WIRE 240 320 240 176
WIRE 288 64 208 64
WIRE 288 320 240 320
WIRE 288 320 288 64
WIRE 384 32 208 32
WIRE 384 144 208 144
WIRE 384 320 288 320
WIRE 384 320 384 224
FLAG 128 352 0
SYMBOL ltline 160 160 R0
SYMATTR InstName O1
SYMATTR Value RG59U
SYMBOL voltage -128 144 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value SINE(0 1 1e6)
SYMBOL res 368 240 M180
WINDOW 0 36 76 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName R2
SYMATTR Value 75
SYMBOL ltline 160 48 R0
SYMATTR InstName O2
SYMATTR Value RG59U
TEXT -152 456 Left 0 !.model RG59U LTRA(len=5.28e6 R=51.6e-3 L=0.115u C=20.5p)
TEXT -162 506 Left 0 !.tran 0 1m 0 1u
TEXT 496 456 Left 0 ;(Belden 8263)

RG59U.plt

[Transient Analysis]
{
Npanes: 3
Active Pane: 2
{
traces: 1 {524290,0,"v(n001)/Ia(O1)"}
X: ('u',0,0,8e-005,0.0008)
Y[0]: (' ',0,0,10,100)
Y[1]: ('_',0,1e+308,0,-1e+308)
Units: "Ohm" (' ',0,0,0,0,10,100)
Log: 0 0 0
GridStyle: 1
},
{
traces: 1 {524291,0,"v(n001)/Ia(O2)"}
X: ('u',0,0,8e-005,0.0008)
Y[0]: (' ',0,0,10,100)
Y[1]: ('_',0,1e+308,0,-1e+308)
Units: "Ohm" (' ',0,0,0,0,10,100)
Log: 0 0 0
GridStyle: 1
},
{
traces: 1 {524292,0,"v(n001)/Ia(O3)"}
X: ('u',0,0,8e-005,0.0008)
Y[0]: (' ',0,0,10,100)
Y[1]: ('_',0,1e+308,0,-1e+308)
Units: "Ohm" (' ',0,0,0,0,10,100)
Log: 0 0 0
GridStyle: 1
}
}

 

[Rich Grise]

["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 ?

its hard to terminate infinitely long conductors, as finding the end can
be rather tricky

Nothing tricky about it - just infinitely tedious. ;-)

Cheers!
Rich

 

[Rich Grise]

Most are


Run the LTSpice simulation below, three cases of 1000 miles of RG59-U,
terminated. shorted, and open at 1 MHz. You'll find all 3 cases look like
75 ohms.

I'm guessing, for the first, say, 2 or so microseconds?

;-)
Rich

 

[Cliff]

Yes, electrons don't travel very fast at all. Nowhere near c.

But if I stick a few in one end of a long wire a few others
want to pop out the other end quite quickly.

 

[Cliff]

here I was thinking the propagation velocity varied as 1/sqrt(Ur*Er)

where Ur and Er are the relative permeability and permittivity,
respectively.

Which came first? The propagation velocity or Ur and Er?

Is there a NG about chickens & eggs?

 

[Bob Myers]

Which came first? The propagation velocity or Ur and Er?

They're different ways of expressing the same basic thing (well,
at least if you also have U0 and E0).

Bob M.

 

[Terry Given]

Which came first? The propagation velocity or Ur and Er?

Is there a NG about chickens & eggs?

I've always thought the whole chicken-and-egg question does little more
than demonstrate that philosophers are all a bit thick. define "chicken"
- pretty soon you have some form of a genetic spec. At some point during
the evolution of a chicken, a couple of non-chickens did the wild thing
(made the beast with two beaks?), and by the miracle of recombinant DNA
ended up with a chicken egg. Ergo the egg came first. It also doesnt
matter what you decide to call a chicken.... QED.

Cheers
Terry

 

[NunYa Bidness]

Read a textbook for cripe's sake.

<snip>

I would venture to say that he knows more about it than someone with
your attitude likely ever will.

He could likely quote Beverly from cover to cover (a slight
exaggeration)... can you even come close? Or a better question would
be are you even familiar with him at all?

 

[NunYa Bidness]

http://www.allaboutcircuits.com/vol_2/chpt_13/3.html

Nice smack!

 

[NunYa Bidness]

Correct. There must be a return path to the generator or battery.

The word you want is "source". There must be a return path to the
source for flow to occur.

 

[NunYa Bidness]

["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.

Freudian shlip? Wear gloves!