Cable Ohm Question
 

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?

Just a question that has bugged me for a while.

Thanks
Brian

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?

Just a question that has bugged me for a while.

Thanks
Brian


Wikipedia is your freind Brian :)

http://en.wikipedia.org/wiki/Coax

Cable Ohm Question
 

In article .com,
wrote:
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?

50, 75, and 300 ohms refer to the characteristic impedances of the cables.
In simple terms, impedance can be thought of as AC resistance (an ohmmeter
measures DC resistance).

The length of the cable doesn't affect its characteristic impedance, but it
does affect signal loss. Fortunately, most cables have low loss at
shortwave frequencies.

--
Bill McFadden http://www.rdrop.com/users/billmc
CAUTION: Don't look into laser beam with remaining eye.

Cable Ohm Question
 

Bool Poosey,, I have to watch Death of a Cyclist flick on ''Electric
Ice'' Radio TB now.
cuhulin

Cable Ohm Question
 

Climbe up the ladder and wait for me!!!! Wallace Beery in that old
movie.

Bungalow Hotel in Vinh Long,Vietnam in 1964 didn't have a stairway up to
the second floor.I once climbed up that ladder,, if y'all get me driff?
www.devilfinder.com Bungalow Hotel Vinh Long Vietnam

Watch m II come along and say I raped that woman in Vinh Long.
I did not,,, she gave it to me for free.
cuhulin,not a rapist

Cable Ohm Question
 

I gave her five dollars,,, that was big money back in those days.
cuhulin

Cable Ohm Question
 

What the H E double hockey stick are you talkin' about?

I want some of whatever you are having.

Brian

wrote in message
...
I gave her five dollars,,, that was big money back in those days.
cuhulin




--
Posted via a free Usenet account from http://www.teranews.com

Cable Ohm Question
 

Brian isn (move doggy) cracy.
cuhulin

Cable Ohm Question
 

Bool sheet,,, doggy hasme figgers loccked ozy,Thang God I am not thhat
crazy#
cuhulin

Cable Ohm Question
 

In article .com,
wrote:

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?

Just a question that has bugged me for a while.

Coax and twin lead cables are transmission lines so 50 ohm coax, 75 ohm
coax, and 300 ohm twin lead refer to the complex impedance not
resistance. Look up transmission line theory.

You could use a network analyzer or TDR (time domain reflectometry) to
measure transmission line impedance. A DVM only measures resistance at
DC.

--
Telamon
Ventura, California

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

Cable Ohm Question
 

I think the needle would bottom out,wouldn't it?
cuhulin

Cable Ohm Question
 

Frank Dresser wrote:


"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


In this discussion you can't arbitrarily separate AC and DC components. The
DC pulses you speak of are a summation of a DC term plus AC components
based up on the repetition and duration of the pulses. Assuming that these
are slow pulses from connecting and disconnection the meter, there would be
significant low frequency content.

Hooking up a DC voltmeter to an infinitely long line is something that
requires you to look at the transient response of the system as opposed to
what would normally be viewed in a steady state manner.

Since the papers I referenced show the low frequency behavior looking
capacitive, I would expect the ohmmeter readings to look similar to one
trying to measure a capacitor.

craigm

Cable Ohm Question
 

HFguy wrote:
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

nice work.

I found the following URL in room 324^1345

http://en.wikipedia.org/wiki/Hilbert...he_Grand_Hotel


mike

Cable Ohm Question
 

In article IYHSg.35567$bf5.18095@edtnps90, m II wrote:
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?

Funny, I just heard that on the the shortwave, in this Wednesday's BBC
documentary, Heather Couper on the History of Infinity. (13:00 and
18:00 UTC in the BBC Asian track on 6195, 9740 or 7160).

You just go to the occupants of room 1 and ask them transfer to
the next room, and so on. There's always another room.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)

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. :) )


craig

OK, you've got a point. Stated in plain English, my imaginary transmission
line doesn't have any series resistance or dielectric leakage. The
resistance of a long run of transmission line can be significant, and would
be infinite over a infinate length. Any conductance of the dielectric would
limit the DC impedance to some high value in a infinate length.

I just got around to checking out the links, and I see it's a nit worth
picking. One of which I'd have been happy to have picked myself, had I
caught it.

Frank Dresser

Cable Ohm Question
 

Mark Zenier wrote:
In article IYHSg.35567$bf5.18095@edtnps90, m II wrote:

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?


Funny, I just heard that on the the shortwave, in this Wednesday's BBC
documentary, Heather Couper on the History of Infinity. (13:00 and
18:00 UTC in the BBC Asian track on 6195, 9740 or 7160).

You just go to the occupants of room 1 and ask them transfer to
the next room, and so on. There's always another room.

That's supposed to be the solution but wouldn't it take an infinite
amount of time for all the occupants to move? They can't all move
instantaneously. The occupant of room #1 has to tell the one in room #2
to move and so on, ad infinitum.

Cable Ohm Question
 

"m II" wrote in message
news:gxZTg.48395$E67.47910@clgrps13...
HFguy wrote:

You just go to the occupants of room 1 and ask them transfer to
the next room, and so on. There's always another room.

That's supposed to be the solution but wouldn't it take an infinite
amount of time for all the occupants to move? They can't all move
instantaneously. The occupant of room #1 has to tell the one in room #2
to move and so on, ad infinitum.

The moving (ripple?) would take forever, but the inconvenience to each
occupant would be rather short lived. I'm more worried about the new
visitor. If there are already an infinite number of guests in the hotel,
where did the guest appear from? ... and are there fire regulations
being broken by overbooking the rooms?





mike (infinity+1) II

Cable Ohm Question
 

"m II" wrote in message
news:gxZTg.48395$E67.47910@clgrps13...
HFguy wrote:

You just go to the occupants of room 1 and ask them transfer to
the next room, and so on. There's always another room.

That's supposed to be the solution but wouldn't it take an infinite
amount of time for all the occupants to move? They can't all move
instantaneously. The occupant of room #1 has to tell the one in room #2
to move and so on, ad infinitum.

The moving (ripple?) would take forever, but the inconvenience to each
occupant would be rather short lived. I'm more worried about the new
visitor. If there are already an infinite number of guests in the hotel,
where did the guest appear from? ... and are there fire regulations
being broken by overbooking the rooms?

mike (infinity+1) II


And supposing some of the occupants were involved in
"compromising acts" of a nature which mandated that
they were not to be disturbed ?? k35454.

(OT) : Hilbert's Paradox of the Grand Hotel - To Infinity And Beyond !
 

k35454 wrote:
"m II" wrote in message
news:gxZTg.48395$E67.47910@clgrps13...
HFguy wrote:

You just go to the occupants of room 1 and ask them transfer to
the next room, and so on. There's always another room.

That's supposed to be the solution but wouldn't it take an infinite
amount of time for all the occupants to move? They can't all move
instantaneously. The occupant of room #1 has to tell the one in room #2
to move and so on, ad infinitum.

The moving (ripple?) would take forever, but the inconvenience to each
occupant would be rather short lived. I'm more worried about the new
visitor. If there are already an infinite number of guests in the hotel,
where did the guest appear from? ... and are there fire regulations
being broken by overbooking the rooms?

mike (infinity+1) II

Hilbert's Paradox of the Grand Hotel
http://en.wikipedia.org/wiki/Hilbert's_paradox_of_the_Grand_Hotel
What is a "Dox" ? -and may I ask- Why Do We Need A Par-a-Dem
{Pair-of-Them} To Confuse Ourselves ? ? ?

INFINITY - With respect to "The Universe" is a concept that has
a basis in-fact only to the extent at in the past "The Universe"
has been Expanding -and- in the future "The Universe" will be
Expanding. - - - Where "The Universe" is Expanding and forever
getting bigger, And Bigger. AND BIGGER ! - Beyond Our Ability
to Comprehend {Imagine} - THAT IS INFINITY [.]

Now with Respect to the Grand Hotel having an Infinity of Rooms
that are all appear to be occupied with new guests arriving at every
moment-in-time : The New Rooms {Ever-Expanding} are being
created in the Null-Time-between-Time when Guest's Appear.

Therefore We May Conclude that with respect to Infinity :
Time as a Concept is Static -and- Expansion as a Concept is Dynamic.

As Buzz-LightYear says : To Infinity And Beyond !
http://en.wikipedia.org/wiki/Buzz_Lightyear

theoretically speaking - this has been a waste of time ~ RHF {ibid}
[ Remember - No-one has ever attempted . . .
a Double By-Pass Brain Transplant before. ]

Cable Ohm Question
 

"craigm" wrote in message
...
m II wrote:

Frank Dresser wrote:

The
resistance of a long run of transmission line can be significant, and
would be infinite over a infinate length.


Wouldn't the DC resistance between a coax sheath and the inner conductor
actually DECREASE as length increased? An infinitely long cable should
have ZERO resistance between the two, as the dielectric resembles an
infinite number of very high value resistors in parallel. Paralleling
resistors lowers total R.




mike


Both center conductor and shield have series resistance.

craigm


And real world dielectrics are less lossy at DC than real world conductors.
So, the conductor resistance would dominate the conductor resistance -
dielectric conductance ratio over a very long run.

Any ohmmeter will measure the resistance of a few thousand feet of
transmission line. But it would take a sensitive meter at much higher
voltage to read the slight leakage current in that same amount of line.

But I don't know if that would be true at all temperatures, though.

Frank Dresser

Cable Ohm Question
 

craigm wrote:

Both center conductor and shield have series resistance.

True enough. How and when would the flow stabilize and at what
percentage between zero amps and a full short? I get the feeling that
this may be leading towards the characteristic impedance of the line, eg
50 ohms..




mike

Cable Ohm Question
 

What it was was an old wall outlet in the Bell South woman's house next
door and it was leading to a full short.It wasen't making a good
connection,their tv set and stereo and window unit airconditioner and
the lights were dimming low.She replaced that wall outlet and now
everything is honky dory again over there.
cuhulin

Cable Ohm Question
 

m II wrote:

HFguy wrote:

You just go to the occupants of room 1 and ask them transfer to
the next room, and so on. There's always another room.


That's supposed to be the solution but wouldn't it take an infinite
amount of time for all the occupants to move? They can't all move
instantaneously. The occupant of room #1 has to tell the one in room
#2 to move and so on, ad infinitum.


The moving (ripple?) would take forever, but the inconvenience to each
occupant would be rather short lived. I'm more worried about the new
visitor. If there are already an infinite number of guests in the hotel,
where did the guest appear from? ... and are there fire regulations
being broken by overbooking the rooms?

mike (infinity+1) II

Good point. I suppose the new visitor came from another universe. ;-)