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Author Topic: Dipol - FD3 - FD4  (Read 3849 times)
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TA4AU
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« on: December 01, 2010, 03:54:26 PM »

Hi All.

I hear one friend say me " Dipol antenna or multi band FD3 or FD4 need minimum 8 meter up the ground or roof" is correct ? I cant up  8 meter over the my roof max. 4-5 meter.
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K1JJ
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"Let's go kayaking, Tommy!" - Yaz


« Reply #1 on: December 01, 2010, 09:14:09 PM »

Hi Rasid,

The optimum height above the ground or roof depends upon the frequency and the distance (take off angle) you desire.

Regardless of how high the antenna is, a roof, especially a metal roof, will have a negative effect on the antenna pattern if the roof is 1/8 wavelength away or closer. (35' on 75M.)


If there is no roof, then 1/4 wavelength above ground is good for higher angle local skip work. For DX work, you want the antenna up at least  3/8 wavelength and the best is 1/2 wavelength high. (130' for 75M)    If a roof is involved, the house wiring and plumbing can have an unpredictable bad effect on the pattern.  This holds true for 40-10M too, except 1/2 wavelength becomes a smaller number.

So to answer your question, 4-5 meters high is a good height for 10M DX or 20 M local work. (Local being higher angle signals into Europe from Turkey, etc)    On 40M this is about 1/8 wavelength high and very good for closer in work.  You will still be able to work stateside, but you may be 10db weaker than if the antenna were up at 1/2 wavelength or higher.

Can you download EZNec software? You will have fun trying different antennas and learn a lot too.

Hope this helps.

Tom, K1JJ


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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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There's nothing like an old dog.
KA2DZT
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« Reply #2 on: December 01, 2010, 11:40:49 PM »

Hi Rasid,

The optimum height above the ground or roof depends upon the frequency and the distance (take off angle) you desire.

Regardless of how high the antenna is, a roof, especially a metal roof, will have a negative effect on the antenna pattern if the roof is 1/8 wavelength away or closer. (35' on 75M.)


If there is no roof, then 1/4 wavelength above ground is good for higher angle local skip work. For DX work, you want the antenna up at least  3/8 wavelength and the best is 1/2 wavelength high. (130' for 75M)    If a roof is involved, the house wiring and plumbing can have an unpredictable bad effect on the pattern.  This holds true for 40-10M too, except 1/2 wavelength becomes a smaller number.

So to answer your question, 4-5 meters high is a good height for 10M DX or 20 M local work. (Local being higher angle signals into Europe from Turkey, etc)    On 40M this is about 1/8 wavelength high and very good for closer in work.  You will still be able to work stateside, but you may be 10db weaker than if the antenna were up at 1/2 wavelength or higher.

Can you download EZNec software? You will have fun trying different antennas and learn a lot too.

Hope this helps.

Tom, K1JJ




Leave it to JJ to confuse everyone.

Tom, after reading your answer,  I forgot what the OP's question was.

Makes me want to go outside and spray Miracle Grow on my tower.

Fred
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K1JJ
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"Let's go kayaking, Tommy!" - Yaz


« Reply #3 on: December 02, 2010, 10:57:46 AM »

Duh... I cornfuse myself most of the time - why should I spare everyone else?   Wink


T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
flintstone mop
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« Reply #4 on: December 02, 2010, 12:03:25 PM »

Duh... I cornfuse myself most of the time - why should I spare everyone else?   Wink


T
Don't worry Tom.....Your post was perfectly clear about height above ground or roof and operating freq. High angle, local, DX.
Maybe the iTunes was too loud in the earpiece.
(for the OTHER Fred)
HA!

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Fred KC4MOP
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