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Transmission Line Demonstrators

C

chris7007

Jan 1, 1970
0
Hi, my name's Chris and currently finishing my college degree in EE. I
was really interested in leaving some sort of legacy for my department
and my professor suggested building a Transmission Line Demonstrator
for her RF and EMC class. I looked up online and could only find 2
sites, one that sold them, and another that gave a very short
description.

Has anyone here ever tried to build one or has any idea what it
entails, as well as any references anyone might have? The help is
greatly appreciated. This isn't for a project by the way, its just one
thing I want to do for my school
 
J

John Larkin

Jan 1, 1970
0
Hi, my name's Chris and currently finishing my college degree in EE. I
was really interested in leaving some sort of legacy for my department
and my professor suggested building a Transmission Line Demonstrator
for her RF and EMC class. I looked up online and could only find 2
sites, one that sold them, and another that gave a very short
description.

Has anyone here ever tried to build one or has any idea what it
entails, as well as any references anyone might have? The help is
greatly appreciated. This isn't for a project by the way, its just one
thing I want to do for my school

A piece of rope works pretty well. It can demonstrate termination,
reflection in both polarities, loss, dispersion, stuff like that, and
you can *see* what's going on.

John
 
L

LVMarc

Jan 1, 1970
0
chris7007 said:
Hi, my name's Chris and currently finishing my college degree in EE. I
was really interested in leaving some sort of legacy for my department
and my professor suggested building a Transmission Line Demonstrator
for her RF and EMC class. I looked up online and could only find 2
sites, one that sold them, and another that gave a very short
description.

Has anyone here ever tried to build one or has any idea what it
entails, as well as any references anyone might have? The help is
greatly appreciated. This isn't for a project by the way, its just one
thing I want to do for my school


Chris,

You can build a very nice legacy device by making a coaxial air line.

this would be two tubes one centered within the other one. by selecting
the id an od you can very close 50 ohm structure, a structure 60- 42
ohms would be great.

place a suitable rf connector on each to terminate the air line. the
connector wail enable connecting sources or vna on one end, and loads,
or test device on the other end.

In the middle of the air txline make a small hole 3/8 od for inserting
voltage current or power flow probes.

I would make the air line 5-12 inches to make is useful an practical to
handle mount etc.


Just measuring the tx lines impedance and loss tangent is an intersing
exercise for graduate students.

undergrads can watch what happens for matched and mis matched
conditions,,,, others may use it to set up a know field at the hole
access pint and then use this field to calibrate field sensor that
other graduate students can make to obtain various bandwidths,
sensiivites, etc.

Lots of fun, I have done this myself..
Best regards,

marc Popek

www.fwt.niat.net and follow the links to the Center for energy research

http://www.youtube.com/profile?user=LVMarc

products
 
V

Vladimir Vassilevsky

Jan 1, 1970
0
chris7007 said:
Hi, my name's Chris and currently finishing my college degree in EE. I
was really interested in leaving some sort of legacy for my department
and my professor suggested building a Transmission Line Demonstrator
for her RF and EMC class. I looked up online and could only find 2
sites, one that sold them, and another that gave a very short
description.

Has anyone here ever tried to build one or has any idea what it
entails, as well as any references anyone might have? The help is
greatly appreciated. This isn't for a project by the way, its just one
thing I want to do for my school

I built a Lecher line demo with a trivial 150MHz tube generator for school
somewhat 25 years ago. It is very simple and illustrative. Still working in
our days.
BTW, doing that with modern RF transistors would be a lot more complicated.

Vladimir Vassilevsky
DSP and Mixed Signal Consultant
www.abvolt.com
 
B

Bob

Jan 1, 1970
0
John Larkin said:
A piece of rope works pretty well. It can demonstrate termination,
reflection in both polarities, loss, dispersion, stuff like that, and
you can *see* what's going on.

John

John,

Hmmm...interesting idea. I can see how you'd show a pulse into a short
(getting -A coming back with zero amplitude at the end) but how would you
demonstrate the pulse into an open (getting +A coming back and 2A at the
end)?

In the mean time, I'm off to Home Depot to get some rope.

Thanks.

Bob
 
J

John Popelish

Jan 1, 1970
0
Bob said:
Hmmm...interesting idea. I can see how you'd show a pulse into a short
(getting -A coming back with zero amplitude at the end) but how would you
demonstrate the pulse into an open (getting +A coming back and 2A at the
end)?

Hang it.
 
B

Bob

Jan 1, 1970
0
John Popelish said:

I beg your pardon? Why don't you go...oh, I see.

Yeah, that's what I was thinking, too. Okay, now I'm really gonna go to Home
Depot.

Bob
 
T

Tom Bruhns

Jan 1, 1970
0
Hi, my name's Chris and currently finishing my college degree in EE. I
was really interested in leaving some sort of legacy for my department
and my professor suggested building a Transmission Line Demonstrator
for her RF and EMC class. I looked up online and could only find 2
sites, one that sold them, and another that gave a very short
description.

Has anyone here ever tried to build one or has any idea what it
entails, as well as any references anyone might have? The help is
greatly appreciated. This isn't for a project by the way, its just one
thing I want to do for my school

The best I've seen, though tedious to make, is a torsion system.
There's a central rod, with connectors at each end, and cross pieces.
The impedance depends on the moment of the cross pieces; the system I
saw used uniform center rods, I believe. (It was a lonnnnggg time
ago, in Bell Labs educational films.) It's especially impressive if
you paint the ends of the cross pieces with fluorescent paint...

I'd say there were perhaps four cross pieces per foot, with central
rods about three or four feet long. The system could be made from
plastic rods or wooden dowels.

The advantage over rope is that you can demonstrate specific
reflection properties, and you can make tapered lines to match
impedances over a range of frequencies. The system in the film had a
motor that could be used for sinusoidal excitation; it just needs to
pull up and down on the end of a cross piece. It must also have had
loads, though I don't remember them specifically.

The images were so vivid to me that I still remember them when
thinking about transmission line problems.

If you decided to do it that way, you could perhaps enlist the help of
some other students and make it a more interesting team effort.

Cheers,
Tom
 
J

John Larkin

Jan 1, 1970
0
John,

Hmmm...interesting idea. I can see how you'd show a pulse into a short
(getting -A coming back with zero amplitude at the end) but how would you
demonstrate the pulse into an open (getting +A coming back and 2A at the
end)?

In the mean time, I'm off to Home Depot to get some rope.

Thanks.

Bob

As JP says, you can hang it. But propagation is nicer with some
tension on the rope, so "terminate" the end into a longish piece of
fine string or fishing line. That's not a true open, but it is a
transition to a much higher impedance line, so you will get an almost
100% non-inverted reflection.

Hey, you can even "capacitively" load a section of the line, lumped or
distributed, and see the wave slow down in that section.

John
 
R

Robert

Jan 1, 1970
0
Tom Bruhns said:
The best I've seen, though tedious to make, is a torsion system.
There's a central rod, with connectors at each end, and cross pieces.
The impedance depends on the moment of the cross pieces; the system I
saw used uniform center rods, I believe. (It was a lonnnnggg time
ago, in Bell Labs educational films.) It's especially impressive if
you paint the ends of the cross pieces with fluorescent paint...

I'd say there were perhaps four cross pieces per foot, with central
rods about three or four feet long. The system could be made from
plastic rods or wooden dowels.

The advantage over rope is that you can demonstrate specific
reflection properties, and you can make tapered lines to match
impedances over a range of frequencies. The system in the film had a
motor that could be used for sinusoidal excitation; it just needs to
pull up and down on the end of a cross piece. It must also have had
loads, though I don't remember them specifically.

The images were so vivid to me that I still remember them when
thinking about transmission line problems.

If you decided to do it that way, you could perhaps enlist the help of
some other students and make it a more interesting team effort.

Cheers,
Tom

Like this one?

http://home.gwi.net/~jdebell/pe/cj/v15-6.htm

<snip>

"You see, the behavior of radio waves has always been hard for me to keep
straight in my mind; yet one must understand this subject thoroughly in
order to have a clear knowledge of such things as resonance,
impedance-matching, standing wave ratio, and antenna theory. I was talking
to my high school science teacher back home about it recently, and he
suggested that I build a wave machine as described by Dr. John N. Shive,
Director of Education and Training of the Bell Labs, in his little book
called Similarities in Wave Behavior. This booklet tells how to build the
machine and describes several experiments that can be performed with it.
Well, Carl built one, and that's what we want to show you tonight."

<snip>

Robert
 
B

Bob

Jan 1, 1970
0
Like this one?

http://home.gwi.net/~jdebell/pe/cj/v15-6.htm

<snip>

"You see, the behavior of radio waves has always been hard for me to keep
straight in my mind; yet one must understand this subject thoroughly in
order to have a clear knowledge of such things as resonance,
impedance-matching, standing wave ratio, and antenna theory. I was talking
to my high school science teacher back home about it recently, and he
suggested that I build a wave machine as described by Dr. John N. Shive,
Director of Education and Training of the Bell Labs, in his little book
called Similarities in Wave Behavior. This booklet tells how to build the
machine and describes several experiments that can be performed with it.
Well, Carl built one, and that's what we want to show you tonight."

<snip>

Robert

That is excellent. What a simple idea, and should be very effective at
demonstrating the fundamentals. I've located Dr. Shive's book at a local
bookstore and I'll pick it up tomorrow ($10 for the teacher's edition).

Thanks.

Bob
 
J

John Popelish

Jan 1, 1970
0
John said:
As JP says, you can hang it. But propagation is nicer with some
tension on the rope, so "terminate" the end into a longish piece of
fine string or fishing line. That's not a true open, but it is a
transition to a much higher impedance line, so you will get an almost
100% non-inverted reflection.

And also a much more uniform impedance. A hanging rope has
an increasing tension as you go up toward the anchor, and
the impedance is a function of the mass per length and
tension at any point.
 
G

Guy Macon

Jan 1, 1970
0
I was playing around with a bunch of repelling magnets in a
horizontal clear plastic tube a while back, and they behaved
a lot like a transmission line.
 
R

Ross Herbert

Jan 1, 1970
0
Hi, my name's Chris and currently finishing my college degree in EE. I
was really interested in leaving some sort of legacy for my department
and my professor suggested building a Transmission Line Demonstrator
for her RF and EMC class. I looked up online and could only find 2
sites, one that sold them, and another that gave a very short
description.

Has anyone here ever tried to build one or has any idea what it
entails, as well as any references anyone might have? The help is
greatly appreciated. This isn't for a project by the way, its just one
thing I want to do for my school

I assume you are not referring to high voltage or "power transmission
lines"? EE could be Electrical Engineering or Electronics Engineering.

If you have some basic electronics test gear and a roll of coax then
you only need to apply the theory;
http://www.physics.udel.edu/~jqx/Phys245/lab/lines.html

Or this http://www.ewh.ieee.org/soc/es/Nov1998/09/BEGIN.HTM

Is this the demonstrator you found?
http://www.ljgroup.com/products/product.asp?id=245
 
M

Michael A. Terrell

Jan 1, 1970
0
Bob said:
Hmmm...interesting idea. I can see how you'd show a pulse into a short
(getting -A coming back with zero amplitude at the end) but how would you
demonstrate the pulse into an open (getting +A coming back and 2A at the
end)?

In the mean time, I'm off to Home Depot to get some rope.



Buy some extra rope to hang the Donkey and the 'Morphmister', while
you're at it.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
J

John Larkin

Jan 1, 1970
0
Buy some extra rope to hang the Donkey and the 'Morphmister', while
you're at it.

But think of the hassle of disposing of the giant, smelly, bloated
carcasses. The toxic waste fees would be outrageous.

John
 
J

John Larkin

Jan 1, 1970
0
And also a much more uniform impedance. A hanging rope has
an increasing tension as you go up toward the anchor, and
the impedance is a function of the mass per length and
tension at any point.


Which brings up the interesting idea of demonstrating the wave
behavior in a tapered line.

John
 
J

John Popelish

Jan 1, 1970
0
John said:
Which brings up the interesting idea of demonstrating the wave
behavior in a tapered line.

Crack that whip.
 
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