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



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

"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



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
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

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



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
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.

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.

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



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

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.

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

Hi Jerry,

In response to this, and your email, your wishes are most likely to
evince a deafening silence. If you are trying to survey those who
have built one from a population of those who used them, I think
you've already hit a saturation of 2 possible users. Your own
construction effort would qualify you to expand the population by 50%.

As for why a slab style over a cylinder style. That for me is taken
on faith that greater minds, in the person of HP Metrologists, figured
that one out a long time ago. Myself, I can infer their rationale
that perhaps demands more precision and accuracy than you care to
pursue; but as any path demands a handcrafted solution, why put in 80%
of the effort for a 20% design when 90% effort would double or triple
your return?

Harkening back to my days at Metrology school, I can imagine that the
slab method was chosen because of the inevitable inner line sag that
would inject residual SWR into the system. Sagging between two plates
would seem to me to be a non-issue. Sagging within a cylinder may not
bring enough residual SWR to cause you grief either, but you have to
build and test one to discover the error of your presumption if it
disappoints you.

As for using your scope to eke out the voltage measurements. That is
a tantalizing thought, but the big boys accomplish more with less.
Simplicity is the keyword, with thinking outside of the box. You are
focusing on the literal, absolute voltage measurement when SWR is all
a matter of relativity that affords orders of magnitude more
sensitivity and resolution (and hence accuracy).

Research the Agilent archives for the Metrology papers of the 1960s.
The discussion is very accessible (with only the math necessary to
perform a real measurement) and focused to the concept and the theory.
The writing of that era is a hallmark of clarity.

73's
Richard Clark, KB7QHC