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Message |
    
Crab_apple
New member
Username: Crab_apple
Post Number: 3
Registered: 5-2014
| | Posted on Sunday, May 25, 2014 - 9:35 am: | 
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Do i need a Blaun or RF choke on my base 11 meter antenna? Will a Blaun help my antenna performance in any way? I am running a A99 as of now! I know some folks don't use a Blaun, should i put one on just for good measure? Thanks! |
Tech237
Moderator
Username: Tech237
Post Number: 1791
Registered: 4-2004
| | Posted on Monday, May 26, 2014 - 7:59 am: |
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Will a balun help an A99 - no. Balun stands for Balanced to unbalanced, and is designed to allow you to use an antenna that uses a balanced feed line (300 ohm, 450 ohm twin line) with a radio that uses an unbalanced coax. In some cases an Unun may help. This is basically an unbalanced to unbalanced isolation transformer.
An RF Choke is a whole different ballgame. yes use one. You may not need it, but it won't hurt. Simplest form is to coil up 6-8 turns of coax 6 inches in diameter. I have made these just by coiling the coax, and sometimes wound them around the bottom of a 2 liter coke bottle. Which ever way you use make sure it is taped/cable tied to the mast or supported in some way to keep the strain off of the coax plug.
Neither the unun nor the choke, will help the actual antenna performance, what they will do is reduce the risk of RF flowing down the outside of the shield into the shack. This stray RF causes SWR meters to read wrong, mic to bit when you key up, and the most dreaded of all RFI problems.
Tech237
N7AUS
God made me an athiest, who are you to question his wisdom?
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Crab_apple
New member
Username: Crab_apple
Post Number: 4
Registered: 5-2014
| | Posted on Tuesday, May 27, 2014 - 10:49 pm: |
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Thanks Tech237, I am going to to make me a RF choke and and use it! It sounds like a proper thing to do and a good thing to have on a good base set up! |
Possum_lodge
Junior Member
Username: Possum_lodge
Post Number: 18
Registered: 5-2014
| | Posted on Wednesday, May 28, 2014 - 10:49 am: |
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You need to check the minimum bend radius of the coax before you wind a choke that tight.
If you wind it too tight, you open up the braid and defeat the purpose of the coax - to keep the signal in and the noise out. |
Dale
Senior Member
Username: Dale
Post Number: 2091
Registered: 12-2002
| | Posted on Saturday, May 31, 2014 - 10:10 am: |
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as long as you have a stranded center conductor
and not a soild you should be fine.i found
a site by a ham operator that uses a 8 turn
8 inch diameter rf choke . id give that a try
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
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Tech237
Moderator
Username: Tech237
Post Number: 1795
Registered: 4-2004
| | Posted on Thursday, June 05, 2014 - 2:04 pm: |
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Possum Lodge - it's not so much the issue with the braid, but too tight a bend causes the inner conductor to migrate within the insulator, which then causes the impedance to change. This is the same reason why sweeping curves are used when running coax.
In most cases, unless it is a poorly shielded cable the shield should not spread enough to leak.
Tech237
N7AUS
God made me an athiest, who are you to question his wisdom?
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