| Author |
Message |
    
Plano
Junior Member
Username: Plano
Post Number: 17
Registered: 6-2004
| | Posted on Sunday, October 29, 2006 - 8:21 pm: | 
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I`m running 1/2 heliax from gamma match to radio frre space form the tower to the ground. I have good amount hanging for a loop aroung rotor. The problems is alot of rf running on the outside of heliax. The part on the ground no rf as it goes in the air rf increases. Could this come from a bend in coax. SWR is good 1:2 No shorts. I`m thinking maybe a kink or bend that has got the ground a little to close to hot wire. Any suggestion will be appreciated thanks. I checked rf with feild strength meter. |
Chad
Senior Member
Username: Chad
Post Number: 1185
Registered: 11-2004
| | Posted on Sunday, October 29, 2006 - 10:28 pm: |
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What kind of antenna? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2222
Registered: 9-2004
| | Posted on Sunday, October 29, 2006 - 11:30 pm: |
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i think you need an RF isolator, sometimes called a 1:1 balun.
this will decouple the RF from the outside of the coax.
see that guy with the big dog just above me?
check out his profile in the MEMBERS PICTURES area and he will show you how to build your own.
good luck,
matt |
Plano
Junior Member
Username: Plano
Post Number: 18
Registered: 6-2004
| | Posted on Monday, October 30, 2006 - 7:36 am: |
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Hey chad I`m running an 8 element beam. I didn`t have this problem on a ten element. I changed the heliax to a shorter run (1/2 wavelength) total differant peices of heliax and did lengthing the guy wires by 10 or 12 feet. Maybe I need to break them again. Just did think it make it change that bad. Maybe that particular heliax is bad. |
Tech237
Moderator
Username: Tech237
Post Number: 606
Registered: 4-2004
| | Posted on Monday, October 30, 2006 - 9:11 am: |
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Curiosity: How are you determining that you have RF on the outside of the coax?
Did you change the Heliax at the same time as you changed the beam? If so the problem maybe the antenna and not the coax.
Did you change the guys at the same time as the Heliax?
Try taking a 12" lenght of coax and putting a PL-259 at one end. Prepare the other end for a PL-259 and before installing it fill the gap in between with ferrite beads. Using a joiner place this decoupler between the coax and the antenna right at the antenna. This should remove ant RF on the coax that is due to reflections or feed from the antenna.
I'd also recommend breaking your guys every 11ft (non resonant lenght). It may not be the problem but it wont hurt any. |
Plano
Junior Member
Username: Plano
Post Number: 19
Registered: 6-2004
| | Posted on Monday, October 30, 2006 - 10:13 pm: |
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Tech237 I check it with a field strength meter, tower, guy wires, even rotor cable show all showing reflection. I know to many changes at one time. I changed the heliax, antenna, and guy at the same time. I`m in the process of breaking guy wires (thats something that should have been done anyway.) and getting them away from the antenna a little more, and changeing coax. One at a time. Curious to see what causeing the problem. 500 WATTS COME THRU MY NEIGHBOR STERIO AND PHONE NEVER HAD THAT PROBLEM BEFORE. tHANKS FOR ALL THE ADVICE |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2226
Registered: 9-2004
| | Posted on Monday, October 30, 2006 - 10:55 pm: |
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hmmmm...
you say you checked the coax with a field strength meter.
you say that the RF increases as you go up in the air.
i dont think you are measuring the RF on the outside of the coax.
i think you are measuring the field strength of your antenna, which would logically get stronger the closer you got to the antenna.
i dont think a field strength meter is the right piece of equip. to measure what you are trying to measure.
matt |
Tech237
Moderator
Username: Tech237
Post Number: 607
Registered: 4-2004
| | Posted on Monday, October 30, 2006 - 11:25 pm: |
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Try the decoupler and if you still appear to show RF on the outside of teh coax I would suspect that what Matt just stated may be the case.
Also try using a grounding kit on the heliax near the base of the tower - it might make a difference too. |
Plano
Junior Member
Username: Plano
Post Number: 20
Registered: 6-2004
| | Posted on Tuesday, October 31, 2006 - 11:55 am: |
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I HAVE THE TOWER DOWN i MEASURED THE FIRST BREAK IN THE GUY WIRES IT WAS 9 FEET AND ALMOST 80 FEET UNBROKE. For the frequency I talk on that isn`t good. That was the the only break I had in the guy wires. I was thinking I had them broke more and they were only 10 feet below the antenna. With 4 guys 10 feet below the antenna only broke once isn`t good. There 3 more about 20 feet or more below those that I am going to have to break. After that maybe the guy wires is causeing the problem. I just never seen get feild strength of the rotor cable before. Kid maybe I am getting feild strength reading because of all those guy being unbroke. Istill open to all suggestions. Thanks 237 & kid |
Plano
Junior Member
Username: Plano
Post Number: 21
Registered: 6-2004
| | Posted on Tuesday, October 31, 2006 - 12:23 pm: |
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I broke the guy wires 3` 22` 58` feet These measurement should be good for the frequency I talk on. |
