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   Home   Help Search  
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Author Topic: Dipole  (Read 383 times)
CAPTBASET

Posts: 3




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« on: December 06, 2017, 02:08:38 PM »

Hi there...due to space and property restrictions i installed 40m dipole with one leg Smaller around 2 feet from the other , i want to know how much efficiency loss will be there with one leg smaller...by 2 feet

Thanx

AP2FLY
« Last Edit: December 06, 2017, 02:11:57 PM by CAPTBASET » Logged
WB6BYU
Member

Posts: 17195




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« Reply #1 on: December 06, 2017, 02:22:45 PM »

Assuming you can still tune it for a low SWR, I wouldn't expect much loss in efficiency.

If that means the dipole is not resonant and the SWR is high, then the losses due to SWR
will depend on the feedline length and type.


A common solution when you don't have enough room would be to let the remaining wire
hang down from the end insulator so both legs use the same amount of wire.
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CAPTBASET

Posts: 3




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« Reply #2 on: December 06, 2017, 02:25:22 PM »

Thanx alot for the reply...antenna is resonant on 7.0 mhz rest i control with the Rig tunner (ic 7300) without any problem..
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W5DXP
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Posts: 4211


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« Reply #3 on: December 06, 2017, 02:33:09 PM »

...antenna is resonant on 7.0 mhz ...

It appears that you could take about one foot off the other end to get the resonant point more centered in the 40m ham band.
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HAMHOCK75
Member

Posts: 402




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« Reply #4 on: December 06, 2017, 02:45:28 PM »

I did an EZNEC analysis of your situation making these assumptions.

1. A normal 40M dipole 1/2 wave dipole would be 65 feet long
2. Shortened that by two feet to 63 feet
3. Dipole is up 30 feet
4. Attached the drive at 47.5% of 63 feet = 30 feet ( so 30 feet is one leg, 33 feet is the opposite leg ) The demo program only allows up to 20 segments so I can't get closer than that.

Hard to see much difference from a normal dipole other than being two feet shorter, the frequency shifts up a bit.

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CAPTBASET

Posts: 3




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« Reply #5 on: December 06, 2017, 02:47:38 PM »

Oh.... thanx alot my friend....so now im keeping it the way it is....
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