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Author Topic: Installing a Force 12 Flag pole antenna  (Read 424 times)
W6QW
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Posts: 21




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« on: July 08, 2009, 08:18:49 PM »

If the flagpole (vertical) is ground mounted then the length of the radials is not required to be a quarter wavelength at each operating frequency. The radials help reduce the ground loss in this case so the more the better.  Some people say that about 10 foot lengths are sufficient as long as you have a number of them because the RF current is greatest near the base of the antenna.  I would recommend at least 8-10 radials double that amount if you can.  A screen mesh is even better.  The vertical should work well for you especially on 20 meters and above.
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N3OX
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Posts: 8847


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« Reply #1 on: July 08, 2009, 09:41:09 PM »

". If I install a Force 12 flag pole antenna smack in the middle, my radials would only be approx 10 feet long"

Well, the ones out to the corners can be longer. No reason not to have a square radial field.

You'll be fine, especially if you're comparing against some antenna with even more restrictions than the flagpole.

People get a little overzealous with their radial fields.  That's not to say you couldn't get some more performance out of a bigger one.. but it would be  a change you'd really have to measure... maybe a couple dB, maybe 3dB or a bit more if you're going to be using this on 40m. Certainly worth it if you had the space, but some people stress the need to put in a whole copper mine without checking to see if it's actually doing any good....

Those people make it sound like you're going to have abysmal performance if you don't use a hundred really long radials, and that's not really realistic.

I might recommend putting in a good number (20? 30?) of them in your 20 foot square plot, and go out to the edges if you can, so some of them are longer than 10 feet.

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
NV8G
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Posts: 41




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« Reply #2 on: July 08, 2009, 07:45:16 PM »

I have a small front yard.  It's about 20 feet square.  If I install a Force 12 flag pole antenna smack in the middle, my radials would only be approx 10 feet long. This seems like a problem to me?  Aren't the radials supposed to be at least the same length as the antenna?  It will be 20' tall.  Also, from what I have read, it appears that the more radials there are, the better the performance?   So, b4 I go to the expense of buying this antenna....Can someone tell me, will this work?  Or not?
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WX7G
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Posts: 6319




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« Reply #3 on: July 09, 2009, 03:34:58 AM »

A vertical will work well with radials half the antenna length. A dozen radials will get you to the point of diminishing returns on 30 meters and above, bands where the radiation resistance of the antenna is over 25 ohms. On 40 and 80 meters the efficiency will be lower due to ground losses but you will make contacts.

A remote tuner at the base will give the best performance. If you do feed the antenna with coax and tune it at the shack it will work however line losses can eat up more power than the limited ground system.

If using a remote tuner I would feed it directly or thru a 1:1 current balun and not a 4:1 balun.
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WA3SKN
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Posts: 5554




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« Reply #4 on: July 09, 2009, 04:15:09 AM »

Your plan will work for 20 meters and up.  Don't expect stellar performance on the lower bands.
Yes, the ground plane controls how well a vertical performs, so lots of radials... or maybe a ground screen are in order!
73s.

-Mike.
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