I'm condidering building a slotted line for measuring impedance at 137
MHz. I find no referances to home made lines thru my quick Google search.
Does anyone know of any publication that show how someone has already worked
out the problems of contructing one?

Jerry

Jerry Martes wrote:
I'm condidering building a slotted line for measuring impedance at 137
MHz. I find no referances to home made lines thru my quick Google search.
Does anyone know of any publication that show how someone has already worked
out the problems of contructing one?

Try a Lecher wire system described in 50's ARRL Handbooks.
--
73, Cecil http://www.qsl.net/w5dxp



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"Cecil Moore" wrote in message
...
Jerry Martes wrote:
I'm condidering building a slotted line for measuring impedance at 137
MHz. I find no referances to home made lines thru my quick Google
search.
Does anyone know of any publication that show how someone has already
worked
out the problems of contructing one?

Try a Lecher wire system described in 50's ARRL Handbooks.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil
I thought lecher line measurements used a balanced line.
I'm not smart enough to know how to compensate for any irregulariities
associated with open wire measurements of an unbalanced load. And, it seems
that it would be easy enoughto make a 'good enough' slotted line. But,
since I havent found referance to any home built coaxial slotted lines,
maybe its not as easy as I think.

Jerry

Jerry Martes wrote:

"Cecil Moore" wrote in message
...
Jerry Martes wrote:
I'm condidering building a slotted line for measuring impedance at 137
MHz. I find no referances to home made lines thru my quick Google
search.
Does anyone know of any publication that show how someone has already
worked
out the problems of contructing one?

Try a Lecher wire system described in 50's ARRL Handbooks.
--
73, Cecil http://www.qsl.net/w5dxp



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http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----


Cecil
I thought lecher line measurements used a balanced line.
I'm not smart enough to know how to compensate for any irregulariities
associated with open wire measurements of an unbalanced load. And, it seems
that it would be easy enoughto make a 'good enough' slotted line. But,
since I havent found referance to any home built coaxial slotted lines,
maybe its not as easy as I think.

Jerry

About the only difficulty in doing it (besides cost) I can think of is it
would be hard to find a 5 foot long tube you could cut a slot in and not
have it distort due to relieved stress.

Use a square U channel for a bottom and 2 pieces of L to make the top.

Look up the equation for the impedance of square coax, get brass tubing
(which comes in increaments of 1/32") for the center conductor, make 2
end plates for connectors, screw the thing together. Probably should use
plastic screws for the top so they don't have to be flush on the inside.

Thought about making one myself for grins and giggles, but bought a MFJ
analyzer instead; lot more portable.

--
Jim Pennino

Remove -spam-sux to reply.

Jerry Martes wrote:
I thought lecher line measurements used a balanced line.

Yep, it does. I make all my measurements on the balanced
portion of my line and Smith Chart extrapolate to find out
what is going on in the coax. The approach depends on what
you need to accomplish.
--
73, Cecil http://www.qsl.net/w5dxp



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On Mon, 10 May 2004 03:12:05 GMT, "Jerry Martes"
wrote:

I'm condidering building a slotted line for measuring impedance at 137
MHz. I find no referances to home made lines thru my quick Google search.
Does anyone know of any publication that show how someone has already worked
out the problems of contructing one?

Jerry

Hi Jerry,

It is not all that hard to do in fact. HP solved that problem long
ago by thinking outside of the box by thinking box. As with other
test equipment issues, it is simply a matter of planning and testing
with very simple methods. For those whose greatest physical effort in
Ham radio is sliding a credit card across the showroom display
counter, this is called "work."

Basically you construct your coaxial line with the usual interior
line, but unlike the conventional expectations, you do not try to
emulate the outer portion as a cylinder. You construct the outer
portion as two parallel conductive planes (appropriately shorted to
the connector shells at each end (hence the allusion to box):

view HP 805C Slotted Line picture on ebay at:
http://web.ask.com/redir?bpg=http%3a...html&qte=0&o=0

Where the two planes stand apart, you insert a probe to measure the
potential along the line. The depth of the line within and in between
the two parallel surfaces insures the line isolation (no leakage) as
well as preserving the line characteristic Z.

However, anyway that you look at it (even the lecher line suffers from
this) you run the risk of over coupling and throwing the measurement
into confusion (very simple to make errors). The problem is the probe
will introduce its own SWR and gum up the works if it lacks
sensitivity. I won't bother too much with dimensions here, but
instead offer a formula for such a structu
Zc = (138/sqrt(e))·log(4h/pi·d)
where
e: dielectric constant (= 1 for air)
d: interior line diameter
h: wall separation

You will want to build it long enough to be more than a wavelength of
course.

You will also need to calibrate it to determine the residual SWR it
presents to the system (this will reveal construction errors). Off
hand, I would suggest that the walls be roughly a 2 to 4 cm apart and
at least a 20 cm wide (larger wouldn't hurt).

Build one quick and dirty to get your gross mistakes out of the way
without spending too much time on them. I can guarantee no one here
could build it right the first time (including yours truly). Once
you've got the first pass attempt on the bench, then we can talk about
how to use it right. ;-)

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Mon, 10 May 2004 03:12:05 GMT, "Jerry Martes"
wrote:

I'm condidering building a slotted line for measuring impedance at 137
MHz. I find no referances to home made lines thru my quick Google
search.
Does anyone know of any publication that show how someone has already
worked
out the problems of contructing one?

Jerry

Hi Jerry,

It is not all that hard to do in fact. HP solved that problem long
ago by thinking outside of the box by thinking box. As with other
test equipment issues, it is simply a matter of planning and testing
with very simple methods. For those whose greatest physical effort in
Ham radio is sliding a credit card across the showroom display
counter, this is called "work."

Basically you construct your coaxial line with the usual interior
line, but unlike the conventional expectations, you do not try to
emulate the outer portion as a cylinder. You construct the outer
portion as two parallel conductive planes (appropriately shorted to
the connector shells at each end (hence the allusion to box):

view HP 805C Slotted Line picture on ebay at:

http://web.ask.com/redir?bpg=http%3a...html&qte=0&o=0

Where the two planes stand apart, you insert a probe to measure the
potential along the line. The depth of the line within and in between
the two parallel surfaces insures the line isolation (no leakage) as
well as preserving the line characteristic Z.

However, anyway that you look at it (even the lecher line suffers from
this) you run the risk of over coupling and throwing the measurement
into confusion (very simple to make errors). The problem is the probe
will introduce its own SWR and gum up the works if it lacks
sensitivity. I won't bother too much with dimensions here, but
instead offer a formula for such a structu
Zc = (138/sqrt(e))·log(4h/pi·d)
where
e: dielectric constant (= 1 for air)
d: interior line diameter
h: wall separation

You will want to build it long enough to be more than a wavelength of
course.

You will also need to calibrate it to determine the residual SWR it
presents to the system (this will reveal construction errors). Off
hand, I would suggest that the walls be roughly a 2 to 4 cm apart and
at least a 20 cm wide (larger wouldn't hurt).

Build one quick and dirty to get your gross mistakes out of the way
without spending too much time on them. I can guarantee no one here
could build it right the first time (including yours truly). Once
you've got the first pass attempt on the bench, then we can talk about
how to use it right. ;-)

73's
Richard Clark, KB7QHC

Richard

I'm pretty sure I'll try to make it coax instead of "slab" like HP does
it. I saw some 2 inch copper pipe at Home Depot today. They sell it in 5
foot lengths for about $22.00. I'm OK with using only 1/2 wavelength for
the slotted coax. I thought I might be able to 'get away with' using my
scope for detecting the line voltages. I am wide open for learning that my
approach has extremely difficult to solve problems. It all seems fairly
easy right now.
I was hoping to get a response from someone who either had built a line or
knew of a publication on the pitfalls associated with making a slotted line.

Jerry

On Mon, 10 May 2004 06:22:29 GMT, "Jerry Martes"
wrote:

[Richard's good stuff snipped]

You can lead 'em to water, but you can't make 'em drink.

|
| I'm pretty sure I'll try to make it coax instead of "slab" like HP does
|it. I saw some 2 inch copper pipe at Home Depot today. They sell it in 5
|foot lengths for about $22.00. I'm OK with using only 1/2 wavelength for
|the slotted coax. I thought I might be able to 'get away with' using my
|scope for detecting the line voltages. I am wide open for learning that my
|approach has extremely difficult to solve problems. It all seems fairly
|easy right now.
| I was hoping to get a response from someone who either had built a line or
|knew of a publication on the pitfalls associated with making a slotted line.

Wes

Maybe I missed your point. I am trying to learn how to build a slotted
line for impedance measurements at 137 MHz. It would be real helpfull to me
to see how someone has built one at home. I'd sure appreciate hearing about
how you did it or what you know about how I could build one here in my
garage.
In fact, I'd like to know more about why a person (HAM type) would use the
slab line configuration in preferance to coaxial.

Jerry

"Wes Stewart" wrote in message
...
On Mon, 10 May 2004 06:22:29 GMT, "Jerry Martes"
wrote:

[Richard's good stuff snipped]

You can lead 'em to water, but you can't make 'em drink.

|
| I'm pretty sure I'll try to make it coax instead of "slab" like HP does
|it. I saw some 2 inch copper pipe at Home Depot today. They sell it in
5
|foot lengths for about $22.00. I'm OK with using only 1/2 wavelength for
|the slotted coax. I thought I might be able to 'get away with' using my
|scope for detecting the line voltages. I am wide open for learning that
my
|approach has extremely difficult to solve problems. It all seems fairly
|easy right now.
| I was hoping to get a response from someone who either had built a line
or
|knew of a publication on the pitfalls associated with making a slotted
line.

Jerry Martes wrote:
In fact, I'd like to know more about why a
person (HAM type) would use the slab line
configuration in preference to coaxial....

One advantage of slab line is that when you
drop something like a set screw into the
line, it falls right on through. (Been there,
done that).

I've used the HP slab-line instrument and
obtained very good, repeatable results with
it.

Others have commented that the big advantage
is ease of fabrication, and I have to agree.
Cutting a slot in a water pipe seems like a
lot of trouble for minimum gain.

Another alternative might be a trough line.
This is a slab line with bottom side closed
off. The advantage this would provide is a
means of supporting the center conductor
by means of a longitudinal, dielectric strip
between it and the bottom plate of the line.
A long piece of Teflon fiberglass would be
ideal for this. The line dimensions would
have to be adjusted to maintain a 50-ohm Zo.

Anyway, it's an interesting project. Good
luck with it.

Jim, K7JEB
Glendale, AZ