Is there anyone interested in seeing pictures of a home made VHF slotted
line?? I bought some copper pipe at Home Depot and built a 50 ohm line
that seems to work very well.

Jerry

Jerry Martes wrote:
Is there anyone interested in seeing pictures of a home made VHF slotted
line?? I bought some copper pipe at Home Depot and built a 50 ohm line
that seems to work very well.

Definitely! (I'm always a sucker for VHF test equipment.)

H-P used to make one of these, in the form of a very deep trough-line
with massively braced side castings. There was also a 'lite' copy in the
old ARRL VHF Handbook.

If you can minimize the residual SWR (the variation in probe readings
along the line when terminated in a precision 50R load) and other
sources of variability, then you'll be able to make highly accurate
vector impedance measurements at VHF.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian

This line is showing a reflection of 1/10th of the incident voltage. I
am not inclined to refine the mismatch inherent with this construction at
this time. I dont require this line to be a "lab standard". I might try
to minimize the reflection later.
I tapered the line from 2 inch OD down to BNC in only about 3 1/2 inches.
And, I made no attempt to account for the teflon discs used to hold the
center conductor in the center of the line.
I dont even have enough stuff to evaluate the adapters from N to BNC. I
assume the reflection at 137 MHZ is acceptable to me. I sure cant do
anything about adapters from N to BNC anyway.

The slotted line does provide a flat voltage at the probe for all points
along the slot when it is terminated with the BNC 50 ohm load. Nothing I
have here is quality test equipment.
I'm impressed with the fact that I was able to measure load impedances
pretty accurately when they are outside the 1.5 to 1. VSWR circle.

It impresses me that a slotted line can be so easily constructed with
"Home Depot" stuff and still give alot of information on load impedance..

Jerry



"Ian White, G3SEK" wrote in message
...
Jerry Martes wrote:
Is there anyone interested in seeing pictures of a home made VHF
slotted
line?? I bought some copper pipe at Home Depot and built a 50 ohm line
that seems to work very well.

Definitely! (I'm always a sucker for VHF test equipment.)

H-P used to make one of these, in the form of a very deep trough-line
with massively braced side castings. There was also a 'lite' copy in the
old ARRL VHF Handbook.

If you can minimize the residual SWR (the variation in probe readings
along the line when terminated in a precision 50R load) and other
sources of variability, then you'll be able to make highly accurate
vector impedance measurements at VHF.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Yes, post the pics, instructions, etc, please. Or email to
jocjoatmindspringdotcom, if you prefer. Many thanks.


John



"Jerry Martes" wrote in message
...
Ian

This line is showing a reflection of 1/10th of the incident voltage. I
am not inclined to refine the mismatch inherent with this construction at
this time. I dont require this line to be a "lab standard". I might try
to minimize the reflection later.
I tapered the line from 2 inch OD down to BNC in only about 3 1/2
inches.
And, I made no attempt to account for the teflon discs used to hold the
center conductor in the center of the line.
I dont even have enough stuff to evaluate the adapters from N to BNC. I
assume the reflection at 137 MHZ is acceptable to me. I sure cant do
anything about adapters from N to BNC anyway.

The slotted line does provide a flat voltage at the probe for all points
along the slot when it is terminated with the BNC 50 ohm load. Nothing I
have here is quality test equipment.
I'm impressed with the fact that I was able to measure load impedances
pretty accurately when they are outside the 1.5 to 1. VSWR circle.

It impresses me that a slotted line can be so easily constructed with
"Home Depot" stuff and still give alot of information on load impedance..

Jerry



"Ian White, G3SEK" wrote in message
...
Jerry Martes wrote:
Is there anyone interested in seeing pictures of a home made VHF
slotted
line?? I bought some copper pipe at Home Depot and built a 50 ohm
line
that seems to work very well.

Definitely! (I'm always a sucker for VHF test equipment.)

H-P used to make one of these, in the form of a very deep trough-line
with massively braced side castings. There was also a 'lite' copy in the
old ARRL VHF Handbook.

If you can minimize the residual SWR (the variation in probe readings
along the line when terminated in a precision 50R load) and other
sources of variability, then you'll be able to make highly accurate
vector impedance measurements at VHF.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Sat, 17 Jul 2004 08:30:08 +0100, "Ian White, G3SEK"
wrote:

Jerry Martes wrote:
Is there anyone interested in seeing pictures of a home made VHF slotted
line?? I bought some copper pipe at Home Depot and built a 50 ohm line
that seems to work very well.

Definitely! (I'm always a sucker for VHF test equipment.)

H-P used to make one of these, in the form of a very deep trough-line
with massively braced side castings. There was also a 'lite' copy in the
old ARRL VHF Handbook.

If you can minimize the residual SWR (the variation in probe readings
along the line when terminated in a precision 50R load) and other
sources of variability, then you'll be able to make highly accurate
vector impedance measurements at VHF.
Hello, Ian,
here's a little trivia concerning slotted lines you might find interesting. I
developed all the antenna systems that flew on the World's first weather
satellite, TIROS 1, in late 1957, which flew April 1, 1960. The system operated
on four different frequencies, two around 108 MHz and two around 235 MHz.
Circular polarization was required, and was achieved using four crossed unipoles
working against the body of the satellite. Each unipole used a 1/4wl sleeve for
the high-frequency portion with a coaxial extension for the lower frequency,
decoupled by the sleeve for the higher frequency. The sleeve portion was was
developed to yield a 50 + j0 terminal impedance that included the mutual
impedance of the extended portion. The extension portion was developed to
provide as low an SWR as possible at the lower frequency. The coupling system
for feeding the four radiators with four transmitters simultaneously was
designed in stripline.

Now, getting to the point of the story, the development of the radiating
elements was performed before there were any network analyzers--I performed ALL
the work using only a slotted line for hundreds and hundreds of measurements.
The line was an HP-805, that couldn't cover the frequencies involved, so I used
4:1 scale modeling at 432 and 940 MHz. The radiator development was done using a
single element over a ground plane, with the spacecraft modeled with a 4:1 half
shell mounted on a 4' x 4' aluminum plate for the ground plane.

If you have a copy of Reflections II you can see a picture of my lab setup at
the RCA Laboratories in Princeton, NJ, showing the ground plane and the HP-805
slotted line. Incidentally, in 1957 there were no hand calculators either--my
calculations from the line measurements were all made with a slide rule. Just
picture the amount of work involved using such antiquated equipment compared
with what we could do now using today's more sophisticated instrumentation.

Walt Maxwell, W2DU

Walt wrote:

If you have a copy of Reflections II you can see a picture of my lab
setup at the RCA Laboratories in Princeton, NJ, showing the ground
plane and the HP-805 slotted line.

Did that line just look like you could drive a tank across it, or did
you try?

Incidentally, in 1957 there were no hand calculators either--my
calculations from the line measurements were all made with a slide
rule. Just picture the amount of work involved using such antiquated
equipment compared with what we could do now using today's more
sophisticated instrumentation.

That's the irony of it: if they'd been able to connect modern computing
power to a simple slotted line, they might never have bothered to invent
the network analyser :-)

Actually, slotted lines and computers might just about have overlapped.
I'll bet that, somewhere on an 8-inch disk in a forgotten landfill,
there are programs that say:

Connect Short to Slotted Line and Press Enter
Enter Voltage
Connect 50 ohm Load to Slotted Line and Press Enter
Enter Voltage
Connect ...


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Sat, 17 Jul 2004 20:01:19 +0100, "Ian White, G3SEK"
wrote:

Did that line just look like you could drive a tank across it, or did
you try?

Yes, Ian, you COULD have driven a tank across it, it was constructed of a
massive hunk of aluminum with reinforcing segments to prevent physical
distortion. It measured better than 1.02 SWR with a precision 50-ohm resistive
load.

Actually, slotted lines and computers might just about have overlapped.
I'll bet that, somewhere on an 8-inch disk in a forgotten landfill,
there are programs that say:

Connect Short to Slotted Line and Press Enter
Enter Voltage
Connect 50 ohm Load to Slotted Line and Press Enter
Enter Voltage
Connect ...

Probably so, I still have a few 8" disks lying around, just so I can show and
tell my great grandchildren (and I have five) what the early days of computers
were using for memory.

I'm going to scan the pic in Reflections and email it to you in JPEG format.

Walt, W2DU

Walter Maxwell writes:
snip

Probably so, I still have a few 8" disks lying around, just so I can
show and tell my great grandchildren (and I have five) what the
early days of computers were using for memory.

I'm going to scan the pic in Reflections and email it to you in JPEG
format.

Walt, W2DU

You had 8" floppies? Let me tell you, when I was young we didn't have
any such newfangled nonsense. No, sir, we thought ourselves lucky to
have punch cards. AND we punched them by hand -- none of these fancy
keypunch machines for us (grumble, grumble).

I still do have a box of punch cards somewhere, containing:

1. A simulator written in 3600 Compass assembler, for a hypothetical
machine we had to design. (The 3600 assembly was itself run on an
emulator running on a CDC 6600.)
2. An assembler we wrote for our hypothetical processor.
3. A program written in our hypothetical assembly language, to be
assembled by our assembler and run on our emulated processor. I
don't remember what it did, probably sieve of Eratosthenes or
something.

I'm not sure if the cards are in order any more though :-)

Regards,
Allen
--
Allen Windhorn (507) 345-2782 FAX (507) 345-2805
Kato Engineering (Though I do not speak for Kato)
P.O. Box 8447, N. Mankato, MN 56002

"Walter Maxwell" wrote in message
...
On Sat, 17 Jul 2004 08:30:08 +0100, "Ian White, G3SEK"

wrote:

Jerry Martes wrote:
Is there anyone interested in seeing pictures of a home made VHF
slotted
line?? I bought some copper pipe at Home Depot and built a 50 ohm line
that seems to work very well.

Definitely! (I'm always a sucker for VHF test equipment.)

H-P used to make one of these, in the form of a very deep trough-line
with massively braced side castings. There was also a 'lite' copy in the
old ARRL VHF Handbook.

If you can minimize the residual SWR (the variation in probe readings
along the line when terminated in a precision 50R load) and other
sources of variability, then you'll be able to make highly accurate
vector impedance measurements at VHF.
Hello, Ian,
here's a little trivia concerning slotted lines you might find
interesting. I
developed all the antenna systems that flew on the World's first weather
satellite, TIROS 1, in late 1957, which flew April 1, 1960. The system
operated
on four different frequencies, two around 108 MHz and two around 235 MHz.
Circular polarization was required, and was achieved using four crossed
unipoles
working against the body of the satellite. Each unipole used a 1/4wl
sleeve for
the high-frequency portion with a coaxial extension for the lower
frequency,
decoupled by the sleeve for the higher frequency. The sleeve portion was
was
developed to yield a 50 + j0 terminal impedance that included the mutual
impedance of the extended portion. The extension portion was developed to
provide as low an SWR as possible at the lower frequency. The coupling
system
for feeding the four radiators with four transmitters simultaneously was
designed in stripline.

Now, getting to the point of the story, the development of the radiating
elements was performed before there were any network analyzers--I
performed ALL
the work using only a slotted line for hundreds and hundreds of
measurements.
The line was an HP-805, that couldn't cover the frequencies involved, so I
used
4:1 scale modeling at 432 and 940 MHz. The radiator development was done
using a
single element over a ground plane, with the spacecraft modeled with a 4:1
half
shell mounted on a 4' x 4' aluminum plate for the ground plane.

If you have a copy of Reflections II you can see a picture of my lab setup
at
the RCA Laboratories in Princeton, NJ, showing the ground plane and the
HP-805
slotted line. Incidentally, in 1957 there were no hand calculators
either--my
calculations from the line measurements were all made with a slide rule.
Just
picture the amount of work involved using such antiquated equipment
compared
with what we could do now using today's more sophisticated
instrumentation.

Walt Maxwell, W2DU


Walter

I too used a HP slotted line alot when I was developing antennas in the
1950s. I never actually knew exactly what I was doing, and have forgotten
most of what I once did with confidance. It is coincidantal that my
primary reason for wanting to know the antenna impedance at 137 MHz is
because I learned, a few months ago, that weather pictures could be produced
from VHF satellite signals.
I reasoned that the pattern form two crossed dipoles spaced 1/4 wave apart
and fed in phase could produce a bidirectional pattern with circular
polarization. I thought that set of simple dipoles might be easy for me to
build, if the antenna concept was compatible with the radiation from polar
orbiting satellites, since they travel in a North-South path.

I am aware that the helix antennas are superior to the crossed array I'd
like to build. Still, I am having fun learning about how these antennas
work.

If I cant easily refine this slotted line, I may try building an impedance
meter with the 4 coax lines, 1/8th wave long each. Perhaps the accuracy of
the coax impedance meter will provide the accuracy missing from the slotted
line method. Maybe the two 'devices' can compliment each other.

I was sure pleased with the way this slotted line worked last night when I
fired it up. I am open to any criticism. This is only fun for me. But,
since it seems to work so well, I thought there might be some interest in
home made "Home Depot" quality (low cost) slotted lines for VHF.

Jerry

Walter

I too used a HP slotted line alot when I was developing antennas in the
1950s. I never actually knew exactly what I was doing, and have forgotten
most of what I once did with confidance. It is coincidantal that my
primary reason for wanting to know the antenna impedance at 137 MHz is
because I learned, a few months ago, that weather pictures could be produced
from VHF satellite signals.
I reasoned that the pattern form two crossed dipoles spaced 1/4 wave apart
and fed in phase could produce a bidirectional pattern with circular
polarization. I thought that set of simple dipoles might be easy for me to
build, if the antenna concept was compatible with the radiation from polar
orbiting satellites, since they travel in a North-South path.

I am aware that the helix antennas are superior to the crossed array I'd
like to build. Still, I am having fun learning about how these antennas
work.

If I cant easily refine this slotted line, I may try building an impedance
meter with the 4 coax lines, 1/8th wave long each. Perhaps the accuracy of
the coax impedance meter will provide the accuracy missing from the slotted
line method. Maybe the two 'devices' can compliment each other.

I was sure pleased with the way this slotted line worked last night when I
fired it up. I am open to any criticism. This is only fun for me. But,
since it seems to work so well, I thought there might be some interest in
home made "Home Depot" quality (low cost) slotted lines for VHF.

Jerry

Hi Jerry,

I hink it's great that you can buy materials a Home Depot from which you can
fabricate a slotted line having 50-ohm impedance. With smooth inner and outer
conductors the inherent swr should be low enough for making acceptable
measurements. In addition, if the teflon spacers are thin they should give only
an insignificant discontinuity at 137 MHz.

You might still want to consider the quadrifilar helix. They are being used
nearly exclusively for all frequencies on the NOAA polar-orbiting weather
satellites. While at RCA in 1976 I performed an R&D project on the quad helix by
investigating the radiation patterns and impedances on over 1000 different
configuations. From the data obtained from my measurements, one configuration
fit the requirements for the TIROS-N spacecrafts, which became NOAA spacecraft
once in polar orbit. RCA built the entire series of TIROS spacecraft until RCA
was taken over by GE in 1986.

The report of my R&D investigation appears in Reflections II, and is also
available for downloading from my web page at http://home.iag.net/~w2du. There
is also a chapter in Reflections 1 and 2 that describes two configurations of
the quad helix, one of which is that flying on the NOAA satellites;. The chapter
number is 22, and is also available for downloading from my web page. That
chapter gives the data for constructing the configuration flying on the NOAA
satellites, which uses an infinite balun and self phasing of the helical
elements. If you're not interested in constructing that particular configuration
you can still feed the two helical elementss separately, using commercially made
baluns and a 90° phase shifter.

Jerry, the beautiful aspect of using the quad helix is that you don't have to
point it toward the satellite. Just place it so the beam is vertical and at
least 1/4wl above ground and it'll give you signal from horizon to horizon
without aiming it.

Good luck with whatever configuration you use.

Walt