Mike Coslo wrote:
I'm a real dilettante in these matters, but why would a signal be
reflected if the impedance was incorrect, and not if it was correct?

Dunno why, but that's just the way it is. To see for yourself,
feed a 75 ohm TV through 1000 ft. of 75 ohm coax. Then feed
the same TV through 1000 ft. of 600 ohm ladder-line. How do
you explain no ghosting in the first case and lots of ghosting
in the second case? Seeing is believing.
--
73, Cecil http://www.qsl.net/w5dxp



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They make an instrument called a Time Domain Reflectometer,
you hook it up to transmission lines and it sends out a pulse
and times how long it takes to get back.
The time it takes, reflected pulse polarity, and height says a lot about the
line.
Used for finding faults on telco/cable lines.
Does the same thing with RF lines.
Matched well, no pulse, but you can even see connectors on some of these
TDR's
Googleit, too

"Cecil Moore" wrote in message
...
Mike Coslo wrote:
I'm a real dilettante in these matters, but why would a signal be
reflected if the impedance was incorrect, and not if it was correct?

Dunno why, but that's just the way it is. To see for yourself,
feed a 75 ohm TV through 1000 ft. of 75 ohm coax. Then feed
the same TV through 1000 ft. of 600 ohm ladder-line. How do
you explain no ghosting in the first case and lots of ghosting
in the second case? Seeing is believing.
--
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! =-----

* wrote:

They make an instrument called a Time Domain Reflectometer,
you hook it up to transmission lines and it sends out a pulse
and times how long it takes to get back.
The time it takes, reflected pulse polarity, and height says a lot about the
line.
Used for finding faults on telco/cable lines.
Does the same thing with RF lines.
Matched well, no pulse, but you can even see connectors on some of these
TDR's
Googleit, too

Fascinating stuff! Why don't we use them more for ham radio? this page:
http://www.epanorama.net/circuits/tdr.html even has a diagram for a
homebrew pulse source and diagrams for hooking up same to an
oscilloscope. While not giving SWR, it would show up any connector
faults and crimps in the cable.

- Mike KB3EIA -

"Mike Coslo" wrote in message
...

* wrote:

They make an instrument called a Time Domain Reflectometer,
you hook it up to transmission lines and it sends out a pulse
and times how long it takes to get back.
The time it takes, reflected pulse polarity, and height says a lot about
the
line.
Used for finding faults on telco/cable lines.
Does the same thing with RF lines.
Matched well, no pulse, but you can even see connectors on some of these
TDR's
Googleit, too

Fascinating stuff! Why don't we use them more for ham radio? this page:
http://www.epanorama.net/circuits/tdr.html even has a diagram for a
homebrew pulse source and diagrams for hooking up same to an
oscilloscope. While not giving SWR, it would show up any connector
faults and crimps in the cable.

- Mike KB3EIA -

i use one regularly in my station here. most people don't use them because
a simple swr meter is adequate for testing most antenna./feedline
combinations in use by amateurs.

Dave,

What happens when you ping your antenna? Clearly the spectrum of the pulse
is wider than the bandwidth of a typical antenna, but is there any useful
information?

Tam/WB2TT
"Dave" wrote in message
...

"Mike Coslo" wrote in message
...

* wrote:

They make an instrument called a Time Domain Reflectometer,
you hook it up to transmission lines and it sends out a pulse
and times how long it takes to get back.
The time it takes, reflected pulse polarity, and height says a lot
about
the
line.
Used for finding faults on telco/cable lines.
Does the same thing with RF lines.
Matched well, no pulse, but you can even see connectors on some of
these
TDR's
Googleit, too

Fascinating stuff! Why don't we use them more for ham radio? this page:
http://www.epanorama.net/circuits/tdr.html even has a diagram for a
homebrew pulse source and diagrams for hooking up same to an
oscilloscope. While not giving SWR, it would show up any connector
faults and crimps in the cable.

- Mike KB3EIA -

i use one regularly in my station here. most people don't use them
because
a simple swr meter is adequate for testing most antenna./feedline
combinations in use by amateurs.

on yagi's and other antennas with matching networks you usually just see the
matching network. i use it the most on my beverage antennas which kind of
look like long transmission lines and also to find faults in transmission
lines themselves. with 25 lines or so ranging from about 50' to 500' or so
it makes for a quick check... especially in winter.

"Tam/WB2TT" wrote in message
...
Dave,

What happens when you ping your antenna? Clearly the spectrum of the pulse
is wider than the bandwidth of a typical antenna, but is there any useful
information?

Tam/WB2TT
"Dave" wrote in message
...

"Mike Coslo" wrote in message
...

* wrote:

They make an instrument called a Time Domain Reflectometer,
you hook it up to transmission lines and it sends out a pulse
and times how long it takes to get back.
The time it takes, reflected pulse polarity, and height says a lot
about
the
line.
Used for finding faults on telco/cable lines.
Does the same thing with RF lines.
Matched well, no pulse, but you can even see connectors on some of
these
TDR's
Googleit, too

Fascinating stuff! Why don't we use them more for ham radio? this
page:
http://www.epanorama.net/circuits/tdr.html even has a diagram for
a
homebrew pulse source and diagrams for hooking up same to an
oscilloscope. While not giving SWR, it would show up any connector
faults and crimps in the cable.

- Mike KB3EIA -

i use one regularly in my station here. most people don't use them
because
a simple swr meter is adequate for testing most antenna./feedline
combinations in use by amateurs.

but is there any useful
information?

most people don't use them
because a simple swr meter is adequate for testing
most antenna./feedline
combinations in use by amateurs.

===============================

Following a query, Guru's feel an urgent desire to display their knowledge
about S-parameters, Time domain reflectometers, Circulators, and High power
UHF TV transmitters.

As a consequence, the unfortunate original questioner, with his solitary 1.8
to 30 MHz SWR meter, is entirely forgotten about and remains suspended in
mid-air.
----
Reg, G4FGQ

Quote below.

The on-channel TDR pulse performance of a narrowband antenna can be seen by
controlling the RF bandwidth and spectrum span of the test process to fit
the application. The pulse (ping) itself is modulated onto an RF carrier
set at the operating frequency.

Not practical for most hams, but very useful in evaluating and optimising TV
transmit antenna systems.

If anyone is interested in seeing a jpg of such a measurement, pls e-mail me
directly.

- RF

_____________

"Tam/WB2TT" wrote in message
What happens when you ping your antenna? Clearly the spectrum of the pulse
is wider than the bandwidth of a typical antenna, but is there any useful
information?

"Richard Fry" wrote in message
...
Quote below.

The on-channel TDR pulse performance of a narrowband antenna can be seen
by
controlling the RF bandwidth and spectrum span of the test process to fit
the application. The pulse (ping) itself is modulated onto an RF carrier
set at the operating frequency.
- RF


Duh! I should have known. Pulse it within the BW of the load.
Steve N.

"*" wrote in message ...
They make an instrument called a Time Domain Reflectometer,
you hook it up to transmission lines and it sends out a pulse
and times how long it takes to get back.
The time it takes, reflected pulse polarity, and height says a lot about
the
line.
Used for finding faults on telco/cable lines.
Does the same thing with RF lines.
Matched well, no pulse, but you can even see connectors on some of these
TDR's
Googleit, too

Sorry, *, won't work. TDR only good on wide band systems. Too messy
for this kind of antennas.
--
Steve N, K,9;d, c. i My email has no u's.