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Quarter Back
| | Posted on Monday, August 19, 2002 - 8:23 pm: | 
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Hello - I was helping a friend put up his new Maco 5/8 wave antenna he had this strange thing connected to the bottom of the antenna inline on the coax. It was 4 little squares taped together and he called it a balum. He really did not know what it was also. A owner of a local CB shop told him that it might help reduce TVI so he used it..
THANKS Quarter Back |
bruce
| | Posted on Monday, August 19, 2002 - 9:13 pm: |
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a balum means balanced/unbalance and it will keep TVI down by choking off rf comming back down from your antenna |
Deadly Eyes
| | Posted on Monday, August 19, 2002 - 10:03 pm: |
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Bruce is correct.
It is also a matching device for some antennas.
Baluns come in several ratios. Two of the more popular are 1:1 (one to one) and 1:4 (one to 4).
A 1:1 is as bruce has stated. It keeps the signal currents off the coax and thus helps to prevent RFI.
A 4:1 balun is used in special cases when certain antennas are used and fed with coax. You see certain antennas have a resistance at the feedpoint in the amount of 200 ohms or more. By using a 4:1 balun you are matching the 50 ohm coax to be comfortable with a 200 0hm feed point.
For example lets say an antenna has a feedpoint impedance/reisstance of 200 ohms. If you were to feed the antenna using just 50 ohm coax your SWR would be 4 to 1 at best (400/50). BUT use a 4 to 1 balun with the 50 ohm coax and the SWR drops to to 1:1 or close to it (200/(4*50)).
To some extent this matching ability is true but do not rely entirely on the balun as the sole matching device. The devices are not perfect and sometimes they do fail. ALSO there is loss in the devices. You cannot convert one thing to another thing without tipping the piper.
Consult the ARRL Handbook for more stuff than you ever wanted to know on the topic.
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Bigbob
| | Posted on Tuesday, August 20, 2002 - 10:01 pm: |
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god deadlyeyes yur so good when yu gonna becum a tech for copper and im not funnin i luv "listening" to your explainations. |
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