Dear antenna pros, I've always taken it for grunted about the
300/75/50 ohms of TV ribbon, coax, etc. But how does one measure it?
My ohmsmeter doesn't budge. Is there some standard formula, like wrap
grandma 100 times, with the far end connected to a cheeseburger in her
mouth, the near end finally displaying the characteristic 300/75/50
whatever ohmses?

Dear antenna pros, I've always taken it for grunted about the
300/75/50 ohms of TV ribbon, coax, etc. But how does one measure it?
My ohmsmeter doesn't budge. Is there some standard formula, like wrap
grandma 100 times, with the far end connected to a cheeseburger in her
mouth, the near end finally displaying the characteristic 300/75/50
whatever ohmses?

You don't measure it with most instruments you would have . It is a
calculated value from the size and spacing of the conductors and the
insulation between them. There are ways to measure it but most would not
have them.

Here is a place you can go for an explination.

http://www.epanorama.net/documents/w...impedance.html

Howdy,

These numbers are characteristic impedances of the cables. If you had an
infinite length of it all you would have to do is use an impedance meter and it
would yield the correct C. I.

It is a function of the frequency and the distributed R, L, C, and G of the
cable.

The ARRL Handbook and their antenna book can tell you much.

7e de Jack, K9CUN

The impedance of a transmission line is dependent on the physical
characteristics such as conductor spacing, conductor size and the insulation
characteristics. Impedance is an AC parameter and can't be measured with an
ordinary DC ohmeter. But if you had an infinite length of any transmission
line unterminated and connected an impedance bridge, it would read the
characteristic impedance. The ARRL handbook or any decent antenna books
will have the formulas you want and IIRC there's no factors for grandmas or
cheeseburgers, hi hi.
hank wd5jfr
"Dan Jacobson" wrote in message
...
Dear antenna pros, I've always taken it for grunted about the
300/75/50 ohms of TV ribbon, coax, etc. But how does one measure it?
My ohmsmeter doesn't budge. Is there some standard formula, like wrap
grandma 100 times, with the far end connected to a cheeseburger in her
mouth, the near end finally displaying the characteristic 300/75/50
whatever ohmses?

Henry, WD5JFR wrote:
"can`t be measured with an ordinary ohmmeter. But if you had an infinite
length of any transmission line unterminated and connected an impedance
bridge, it would read the chatracteristic impedance."

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.

Best regards, Richard Harrison, KB5WZI

For you young fellas, it used to be called "surge impedance" just for that
reason.

Steve K/9/d/c/i
"Richard Harrison" wrote in message
...
Henry, WD5JFR wrote:
"can`t be measured with an ordinary ohmmeter. But if you had an infinite
length of any transmission line unterminated and connected an impedance
bridge, it would read the chatracteristic impedance."

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.

Best regards, Richard Harrison, KB5WZI

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.

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

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.

He is right of course. Do you know of anyone that has an infinite length of
transmission line? Or an infinite anything? :-).
73 Gary N4AST