| Author |
Message |
    
852
Intermediate Member
Username: 852
Post Number: 101
Registered: 3-2006
| | Posted on Saturday, October 07, 2006 - 8:07 pm: | 
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With a volt /ohm meter, how would I go about checking for a short in coax? How would I need to set my meter, and what would I touch the probes to?
A newbie needing help
Thomas "852"
CEF750 |
Tech808
Moderator
Username: Tech808
Post Number: 11495
Registered: 8-2002
| | Posted on Saturday, October 07, 2006 - 8:33 pm: |
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852,
With a Volt/Ohm Meter touch both leads to the CENTER CORE and it should show Continuity.
Then touch both leads to the SHIELD and it should show Continuity.
Then touch the leads to both the Center and the Shield and it shoud show -0- or NO Continuity on the meter.
If it shows anything there is a short.
Hope this help's,
Lon
Tech808
CEF808
N9CEF
CVC#2 |
852
Intermediate Member
Username: 852
Post Number: 102
Registered: 3-2006
| | Posted on Saturday, October 07, 2006 - 10:39 pm: |
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Thanks Lon,
Although I've been CB'ing for many years now, I'm just getting into checking some of my own equipment. Thanks for the help.
Thomas "852"
CEF750 |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1382
Registered: 6-2004
| | Posted on Sunday, October 08, 2006 - 12:10 am: |
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Before you do this you should make sure that the coax isn't connected to an antenna, dummy load, or any other device because most of them will show a DC short even is the coax is fine. |
852
Intermediate Member
Username: 852
Post Number: 103
Registered: 3-2006
| | Posted on Sunday, October 08, 2006 - 11:18 am: |
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what should i set my meter on? ohm? DCmA? DCv? or what ? also do I do i touch both leads to the center core or on seperate ends of the coax? same with the shield, on seperate ends or both on same end? Please forgive the stupid questions, but i'm a electronics newbie.
"852"
CEF750 |
Spring
Junior Member
Username: Spring
Post Number: 20
Registered: 7-2006
| | Posted on Sunday, October 08, 2006 - 1:32 pm: |
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Thomas set it to OHM.
ANN
SPRING
CEF800
CVC77 |
Tech237
Moderator
Username: Tech237
Post Number: 546
Registered: 4-2004
| | Posted on Sunday, October 08, 2006 - 1:37 pm: |
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in both cases touch the leads to separate ends of the coax otherwise you will get false readings. |
852
Intermediate Member
Username: 852
Post Number: 104
Registered: 3-2006
| | Posted on Sunday, October 08, 2006 - 4:19 pm: |
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Ok with my meter set to ohm, when I touch the center pins of my pl-259's, one lead touching each pin..The meter swings to full scale which is -0- is this normal? And when I touch the two leads to the outer parts of the pl-259's one lead to each one it swings full scale to -0- and when I touch one lead to the center and one lead to the outer part of the pl-259 the meter doesn't move. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 3257
Registered: 7-2004
| | Posted on Sunday, October 08, 2006 - 7:15 pm: |
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that is telling you that the coax does not have a short in it. an analyzer would be needed to tell you if the impedance is not 50W any longer. a sign of that COULD be a high SWR reading from a setup that has had no changes made to it. a change in coax impedance COULD be the result of water infiltration, or the center conductor no longer being centered inside the braided shield due to any combination of age, heat, tight bends, movement, etc. |
Tech237
Moderator
Username: Tech237
Post Number: 550
Registered: 4-2004
| | Posted on Monday, October 09, 2006 - 10:37 am: |
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To get technical, there is a way to test coax using an RF signal an dummy load and a oscilloscope. This method, called Time Domain Reflectometry (TDR) not only tells you what impedence the coax is, but if it has any problems and gives you an indication how far along the coax that problem is.
If Lon and/or the Forum Masyter think it is worth it, I'll put together an simple article on how this can be done. |
Tech808
Moderator
Username: Tech808
Post Number: 11500
Registered: 8-2002
| | Posted on Monday, October 09, 2006 - 11:12 am: |
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Tech237,
Simon,
Any Helpful information is ALWAYS WELCOME! 
Type it up and post it in the Moderator's area like your other articles and I can re-type it for you and the Forummaster will get it posted.
Lon
Tech808
CEF808
N9CEF
CVC#2 |
Mdiver
Intermediate Member
Username: Mdiver
Post Number: 460
Registered: 11-2003
| | Posted on Monday, October 09, 2006 - 11:55 am: |
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My system took a dump today , Im running a One year old Imax 2000 and new 213-u about a 100 ft. My swr's are at full scale there us a short some were. I ran a Continuity test from the bottom end of the coax to the ant dead short. Can the Imax cause this if so any other help would be great.. looks like Im going to climb the tree and replace it all. the ant and coax are 1 year old
CEF 252
Steve |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 3260
Registered: 7-2004
| | Posted on Monday, October 09, 2006 - 1:07 pm: |
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you DID disconnect the coax from the antenna before testing, steve? just checking  |
Chad
Senior Member
Username: Chad
Post Number: 1140
Registered: 11-2004
| | Posted on Monday, October 09, 2006 - 1:37 pm: |
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The Imax will show a DC short naturally. To check the coax continuity (or lack of) you need to disconnect the antenna.
Chad |
Mdiver
Intermediate Member
Username: Mdiver
Post Number: 461
Registered: 11-2003
| | Posted on Monday, October 09, 2006 - 6:54 pm: |
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Thanks Pat and Chad I need to climb a 100 foot tree to find out I do think the problem is way up there. Again thanks I will let you no
Steve |
