Merry Christmas & Happy New Year 2009
I'd like to take this time to wish all of you a very Merry Christmas.
This is a season of giving, peace, understanding and goodwill among all. I hope that this Christmas will find you among friends and family with good food, good times, and good memories. And I hope too that Santa lines the bottom of your Christmas tree with all the Amateur Radio goodies that it can hold!
Wish you a very happy new year, many nice DX contacts, a lot of pleasure with our hobby and see You in 2009 again!
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How to find a broken or shorthened point of coaxial cable? |
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Suddenly increases the SWR of your antenna? The antenna seems to be good, RIG, too? Maybe there is a fault in the coaxial cable!
There are two usual faults:
1. Broken coaxial cable
2. Shorthened coaxial cable
Broken coaxial cable
It’s not obvious that inner or outer conductor is broken. But sometimes happens it. Unplug coaxial cable from both sides and connect the capacitance meter to the one end and measure the capacity which is marked as C1 (e.g. 180pF). Now connect the capacitance meter to the other end measure the capacity which is marked as C2 (e.g. 120pF).
The point where is coaxial cable broken is done by formula:
D = C1/(C1+C2) x L [m; pF, pF, pF, m]
Where D is the distance from one end to the point where is coaxial cable broken, C1 and C2 are measured capacities and L is overall length of coaxial cable
For example:
3m = 180pF/(180pF + 120pF) x 5m
Coaxial cable is broken 3m far from the end.
Usually is cable broken near ends or walls. So the ratio between both capacities is high.
Shortened coaxial cable
This is common fault of coaxial cable. We need a miliohmameter (measures thousandths and decimals Ohms) to locate the fault point acurately.
Unplug coaxial cable from both sides and connect the miliohmameter to the one end and measure the resistance which is marked as R1 (e.g. 0.8 OHM). ). Now connect the miliohmameter meter to the other end measure the resistance which is marked as R2 (e.g. 0.04 OHM).
The point where is coaxial cable shortened is done by formula:
D = R1/(R1+R2) x L [m; ohm, ohm, ohm, m]
Where D is the distance from one end to the point where is coaxial cable shortened, R1 and R2 are measured resistances and L is overall length of coaxial cable
For example:
4.76m = 0.8 OHM/(0.8 OHM + 0.04 OHM) x 5m
Coaxial cable is shortened 4.76m from the end.
Usually is coaxial cable shortened in the plugs, so the ratio between both resistances is high.
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