Someone sed,

"Reg, G4FGQ observed on these pages long ago that an ordinary ohmmeter would
read Zo if connected to the end of an infinite line. He is right of course."

But the Zo of a line varies with frequency. How will the "ordinary ohmmeter"
do the job at, say, 100 kHz?

73 de jack

"Reg, G4FGQ observed on these pages long ago that an ordinary ohmmeter
would
read Zo if connected to the end of an infinite line. He is right of
course."

But the Zo of a line varies with frequency. How will the "ordinary
ohmmeter"
do the job at, say, 100 kHz?

73 de jack

YOu should get a lot of people calling BS on the Zo changing with frequency.
It does not change at any reasonable frequency for the line. That is at
least anything below 1 ghz for coax.

Zo of ALL real, ordinary, transmission lines changes versus frequency over a
very wide frequency range.

Zo ranges over lots of thousands of ohms at a few cyles of seconds,
thousands of ohms at power frequencies, hundreds of ohms at audio
frequencies, and from tens to a few hundred ohms from 100KHz up to as many
GHz as you like.
---
Reg.


--
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........
"Ralph Mowery" wrote in message
...

"Reg, G4FGQ observed on these pages long ago that an ordinary ohmmeter
would
read Zo if connected to the end of an infinite line. He is right of
course."

But the Zo of a line varies with frequency. How will the "ordinary
ohmmeter"
do the job at, say, 100 kHz?

73 de jack

YOu should get a lot of people calling BS on the Zo changing with
frequency.
It does not change at any reasonable frequency for the line. That is at
least anything below 1 ghz for coax.

"Reg Edwards" wrote in message
...
Zo of ALL real, ordinary, transmission lines changes versus frequency over
a
very wide frequency range.

Zo ranges over lots of thousands of ohms at a few cyles of seconds,
thousands of ohms at power frequencies, hundreds of ohms at audio
frequencies, and from tens to a few hundred ohms from 100KHz up to as many
GHz as you like.
---
Reg.



Are we talking the same thing for Zo ? That a piece of say rg-8 ( whatever
they want to call it now) that is 50 ohm coax is not 50 ohms over its normal
operating frequency range ?

"Reg Edwards" wrote in message
Zo of ALL real, ordinary, transmission lines changes versus frequency
over
a
very wide frequency range.

Zo ranges over lots of thousands of ohms at a few cyles of seconds,
thousands of ohms at power frequencies, hundreds of ohms at audio
frequencies, and from tens to a few hundred ohms from 100KHz up to as
many
GHz as you like.
---
Reg.



Are we talking the same thing for Zo ? That a piece of say rg-8 (
whatever
they want to call it now) that is 50 ohm coax is not 50 ohms over its
normal
operating frequency range ?

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

What is your normal operating frequency range?

Here is Zo typical of cable similar to RG-58 versus frequency.

Nominal Zo = 50 ohms.
Degrees = Angle of Zo.

Freq Zo Degrees
------ ------- -------
10 Hz 3000 -45.0
100 Hz 950 -44.9
1000 Hz 301 -44.1
10 KHz 97 -36.4
100 KHz 54.2 -10.1
1 MHz 50.0 -2.6
10 MHz 48.4 -0.84
100 MHz 48.0 -0.26
1 GHz 47.8 -0.08

Superimposed on the above Zo vs F characteristics are manufacturing
reel-to-reel variations of 2 or 3 percent.
----
Reg, G4FGQ

As most of us do not transmit in the audio range, your own data shows a
range of 50 to 47.8 Ohms for normal ham use. Close enough for government
work, at least as far as I am concerned..

"Reg Edwards" wrote in message
...

"Reg Edwards" wrote in message
Zo of ALL real, ordinary, transmission lines changes versus frequency
over
a
very wide frequency range.

Zo ranges over lots of thousands of ohms at a few cyles of seconds,
thousands of ohms at power frequencies, hundreds of ohms at audio
frequencies, and from tens to a few hundred ohms from 100KHz up to as
many
GHz as you like.
---
Reg.



Are we talking the same thing for Zo ? That a piece of say rg-8 (
whatever
they want to call it now) that is 50 ohm coax is not 50 ohms over its
normal
operating frequency range ?

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

What is your normal operating frequency range?

Here is Zo typical of cable similar to RG-58 versus frequency.

Nominal Zo = 50 ohms.
Degrees = Angle of Zo.

Freq Zo Degrees
------ ------- -------
10 Hz 3000 -45.0
100 Hz 950 -44.9
1000 Hz 301 -44.1
10 KHz 97 -36.4
100 KHz 54.2 -10.1
1 MHz 50.0 -2.6
10 MHz 48.4 -0.84
100 MHz 48.0 -0.26
1 GHz 47.8 -0.08

Superimposed on the above Zo vs F characteristics are manufacturing
reel-to-reel variations of 2 or 3 percent.
----
Reg, G4FGQ

"Reg Edwards" wrote in message
Zo of ALL real, ordinary, transmission lines changes versus frequency
over
a
very wide frequency range.

Zo ranges over lots of thousands of ohms at a few cyles of seconds,
thousands of ohms at power frequencies, hundreds of ohms at audio
frequencies, and from tens to a few hundred ohms from 100KHz up to as
many
GHz as you like.
---
Reg.



Are we talking the same thing for Zo ? That a piece of say rg-8 (
whatever
they want to call it now) that is 50 ohm coax is not 50 ohms over its
normal
operating frequency range ?

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

What is your normal operating frequency range?

Here is Zo typical of cable similar to RG-58 versus frequency.

Nominal Zo = 50 ohms.
Degrees = Angle of Zo.

Freq Zo Degrees
------ ------- -------
10 Hz 3000 -45.0
100 Hz 950 -44.9
1000 Hz 301 -44.1
10 KHz 97 -36.4
100 KHz 54.2 -10.1
1 MHz 50.0 -2.6
10 MHz 48.4 -0.84
100 MHz 48.0 -0.26
1 GHz 47.8 -0.08

Superimposed on the above Zo vs F characteristics are manufacturing
reel-to-reel variations of 2 or 3 percent.
----
Reg, G4FGQ


Think I must have missed the point about REAL transmission lines. Trying to
keep up with too many discussions at one time. I was thinking of the simple
formular where frequency is not mentioned. I do know about the problem of
making the coax exectally the same all the time where even in the same reel
of coax you can get into suckout problems due to slight variations in the
coax.

Someone sed about the characteristic frequency of a transmission line::

"It does not change at any reasonable frequency for the line. That is at
least anything below 1 ghz for coax."

The formula for Zo contains the frequency.

Look it up.

73 de Jack K9CUN

When putting up an antenna, do you use different Zo coax for 2 Vs. 80 meters
to account for frequency change?

The Zo is constant for all practical purposes below Giga Hz freqs.

"JDer8745" wrote in message
...
Someone sed,

"Reg, G4FGQ observed on these pages long ago that an ordinary ohmmeter
would
read Zo if connected to the end of an infinite line. He is right of
course."

But the Zo of a line varies with frequency. How will the "ordinary
ohmmeter"
do the job at, say, 100 kHz?

73 de jack