Cable Ohm Question
 

wrote in message
oups.com...
I am aware of the 50 and 75 ohm coax and the 300 ohm twin lead BUT I am
not sure what this means.

I know about ohms as resistance in resistors but how does that pertain
to cable.

Example - If I have 50 feet of 300 ohm twim lead ribbon cable and 50 ft
of 75 ohm coax could I measure this ohm reading with a meter?

You couldn't read the resistance with a multimeter, at least not in any
practical way. But, a DC meter would read the characteristic impedance of
an infinitely long transmission line.

Imagine that!


Just a question that has bugged me for a while.

Thanks
Brian


If you're still curious, you'll find good explainations in the ARRL
handbooks and the ARRL antenna books. There might be something at your
local library.

Frank Dresser

Cable Ohm Question
 

Frank Dresser wrote:


wrote in message
oups.com...
I am aware of the 50 and 75 ohm coax and the 300 ohm twin lead BUT I am
not sure what this means.

I know about ohms as resistance in resistors but how does that pertain
to cable.

Example - If I have 50 feet of 300 ohm twim lead ribbon cable and 50 ft
of 75 ohm coax could I measure this ohm reading with a meter?

You couldn't read the resistance with a multimeter, at least not in any
practical way. But, a DC meter would read the characteristic impedance of
an infinitely long transmission line.

Imagine that!


Consider these references

http://www.generalcable.co.nz/Techni...impedance% 22

http://www.werple.net.au/~marcop/ciocahalf.htm



Just a question that has bugged me for a while.

Thanks
Brian


If you're still curious, you'll find good explainations in the ARRL
handbooks and the ARRL antenna books. There might be something at your
local library.

Frank Dresser

Cable Ohm Question
 

craigm wrote:


You couldn't read the resistance with a multimeter, at least not in any
practical way. But, a DC meter would read the characteristic impedance of
an infinitely long transmission line.


I'd like to try that, but my electronics dealer only stocks 500 foot
lengths of coax. Will the numerous coax couplings needed to make an
infinitely long chunk of cable ruin the validity of my meter readings?





mike

Cable Ohm Question
 

m II wrote:

craigm wrote:


You couldn't read the resistance with a multimeter, at least not in any
practical way. But, a DC meter would read the characteristic impedance
of an infinitely long transmission line.


I'd like to try that, but my electronics dealer only stocks 500 foot
lengths of coax. Will the numerous coax couplings needed to make an
infinitely long chunk of cable ruin the validity of my meter readings?





mike


Mike,

You should be quoting Frank, not me. Look closer at my post. I posted links
that indicate what Frank wrote my be wrong. Read the material in the links
and decide for yourself.

(You would need a pile of cash to buy enough fittings, anyway. :) )


craigm

Cable Ohm Question
 

craigm wrote:
m II wrote:

craigm wrote:


You couldn't read the resistance with a multimeter, at least not in any
practical way. But, a DC meter would read the characteristic impedance
of an infinitely long transmission line.

I'd like to try that, but my electronics dealer only stocks 500 foot
lengths of coax. Will the numerous coax couplings needed to make an
infinitely long chunk of cable ruin the validity of my meter readings?



Mike,

You should be quoting Frank, not me. Look closer at my post. I posted links
that indicate what Frank wrote my be wrong. Read the material in the links
and decide for yourself.

(You would need a pile of cash to buy enough fittings, anyway. :) )

I mistakenly thought the double set of quotation marks would take care
of the assignation. I should have been more judicious in my clipping.

As for the fittings costing money, well....I was going to purchase only
a few every weekend until the goal was met. How hard can it be? Only two
couplings per roll of cable..shucks, I'll be done in no time.




I read a quiz concerning infinity years ago. It may have been by Martin
Gardner. The problem being that you own a hotel with an infinite number
of rooms. They are ALL occupied. A stranger appears at the registry desk
desperately needing a place to stay, You actually get them one of your
hotel rooms, empty.

How do you do it?




mike

Cable Ohm Question
 

The Truth Behind The Spinach Scare. www.coasttocoastam.com

I bet George Fruitcake Noory has grabbed his pecker and is working
himself in a frenzy on that one.He is so Stupid,he doesn't know how long
he was in the U.S.Navy.One time he said four years,another time he said
nine years.He is the Kookiest KOOK on Earth.You reading this? George
Noory,YOU KOOK.
cuhulin

Cable Ohm Question
 

There are little Animals running around on Mars.~ George Noory,at
www.coasttocoastam.com
cuhulin

Cable Ohm Question
 

m II wrote:
craigm wrote:

m II wrote:

craigm wrote:


You couldn't read the resistance with a multimeter, at least not in
any
practical way. But, a DC meter would read the characteristic
impedance
of an infinitely long transmission line.


I'd like to try that, but my electronics dealer only stocks 500 foot
lengths of coax. Will the numerous coax couplings needed to make an
infinitely long chunk of cable ruin the validity of my meter readings?




Mike,

You should be quoting Frank, not me. Look closer at my post. I posted
links
that indicate what Frank wrote my be wrong. Read the material in the
links
and decide for yourself.

(You would need a pile of cash to buy enough fittings, anyway. :) )


I mistakenly thought the double set of quotation marks would take care
of the assignation. I should have been more judicious in my clipping.

As for the fittings costing money, well....I was going to purchase only
a few every weekend until the goal was met. How hard can it be? Only two
couplings per roll of cable..shucks, I'll be done in no time.




I read a quiz concerning infinity years ago. It may have been by Martin
Gardner. The problem being that you own a hotel with an infinite number
of rooms. They are ALL occupied. A stranger appears at the registry desk
desperately needing a place to stay, You actually get them one of your
hotel rooms, empty.

How do you do it?




mike

http://en.wikipedia.org/wiki/Hilbert's_paradox_of_the_Grand_Hotel

Cable Ohm Question
 

And now I lay me down to sleep,,, I pray the Lord another big bowl of
Spinach to eat,,,,, if I should die before I awake,,,,, I Pray the Lord
my soul to take.
Move over,doggy.
cuhulin

Cable Ohm Question
 

"craigm" wrote in message
...


Mike,

You should be quoting Frank, not me. Look closer at my post. I posted
links
that indicate what Frank wrote my be wrong. Read the material in the links
and decide for yourself.

(You would need a pile of cash to buy enough fittings, anyway. :) )


craigm

I don't see any contridiction between the sites and what I said. Even if
the ohmmeter is a DC instrument, the hypothetical infinately long
transmission line would see only DC pulses. The pulses might last a few
seconds or untill the battery dies or untill the operator meets his eternal
reward or until the whole universe shuts down. I don't see how it matters.
None of these pulses would get into the troublesome "low frequency" area of
the transmission line analysis.

Hey, I could be wrong. But, if so, how am I wrong? What do you think would
happen if you hooked up a DC ohmmeter to an infinately long transmission
line?

Frank Dresser