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Author Topic: Another antenna ground question. . .  (Read 319 times)
N4NOO
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Posts: 106




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« on: July 13, 2003, 06:36:59 PM »

I think I know the answer to this question but I would like to draw on the vast knowledge base of this group.  I am using an Icom 706MKIIG with an AH4 antenna tuning unit.  I have the AH4 mounted on a 2x4 about 6 inches from the ground at the back of my house.  The top (hot) antenna connection has a piece of wire attached to it that runs to the roof line of my house (about 15 feet above the ground) and then on to a tree about 130 feet away with the end about 60 feet above the ground.  The bottom (GND) connection on the AH4 is attached to a piece of #4 bare solid copper wire that is about 2 feet long which is clamped to an 8 foot ground rod.  This rod is attached to two other 8 foot ground rods that are 120 degrees apart forming a 12 foot circle with #4 bare solid copper wire.  The antenna system works well as is, tunes to any ham frequency that I’ve tried, but would more wire radials make an improvement to the current configuration?  

Thanks,

Rick - N4NOO
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ROOT_ADMIN
Member

Posts: 1




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« Reply #1 on: July 13, 2003, 07:51:35 PM »

think of the AH4 as a tuned center insulator... IN THEORY you should have the same amount of copper on both ends.
In practice, prove the best ground you can to the wing nut side, if you do not, you will damage the AH4
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K3WVU
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Posts: 491




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« Reply #2 on: July 13, 2003, 08:07:08 PM »

I have a similar arrangement, except I only have about 70 feet of wire on the 'hot' side.  On the 'ground' side, I have an equal amount of wire that runs on the ground along a plastic fence.  I use #14 insulated wire on both ends, and I use ground cloth staples to fasten the wire to the ground along it's length.  The ground wire portion doesn't have to run in a straight line, either.  I'm a MARS operator and I can tune everything from about 2.5 MHZ to 54 MHZ.
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AA4PB
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Posts: 12770




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« Reply #3 on: July 13, 2003, 08:10:39 PM »

The more radials you put down, the more efficient it will be, especially on the lower bands.
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W9HZ
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Posts: 10




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« Reply #4 on: July 13, 2003, 08:13:37 PM »

I'm not really up on the AH4, but in this configuration, would this be any different then any other long wire or a trapped vertical, where the thinking would be to get as much of a ground screen as possible to reduce ground losses?

Mitch
W9HZ
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K0ABE
Member

Posts: 69




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« Reply #5 on: July 13, 2003, 10:21:32 PM »

Hi Rick,

Yes, the more radials you can lay down the better.  The AH-4 in combination with the IC-706 MKII G, and a long piece of wire gets the job done for sure.  The question is, how much wire should you put down in the form of ground radials?  AND… Of course, the answer is: the more the merrier.

OK, now let’s look at some other ways you can put out a signal with the AH-4.  This past Field Day, a friend and I hung a 140 foot dipole fed with 100 feet of ladder line.  We hung the antenna about 40 feet off the ground and cut off 50 feet of the ladder line.  Hooked one side to the “hot” side of the AH-4 and the other side to the ground side of the tuner.  The AH-4 tuned 160 to 6 meters.  Not bad at all.  We made a good number of contacts with this set up.  Wish I had the room at home to put that antenna up.  The AH-4 owners’ manual says the tuner will only tune 80 to 6 meters.  Don’t have enough room for a 140 foot “flat top” try an inverted V.  Speaking of inverted V, why not try a delta loop.  Just cut the delta for the lowest band you want to work and put the AH-4 at the feed point, remember to hang the delta high enough so nobody cat come in contact with it.

This web site should be helpful to you as well: http://www.hamoperator.com/ah4/ah4.htm  

I hope this helps…

73 Mike KØABE
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W9HZ
Member

Posts: 10




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« Reply #6 on: July 14, 2003, 06:17:34 AM »

K0ABE.....

Hey Mike where have you been hiding???
I havent seen you since back in the days on AOL
Mitch
W9HZ
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K0BG
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Posts: 9861


WWW

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« Reply #7 on: July 14, 2003, 09:59:51 AM »

If the AH-4 is indeed feeding a high impedance (>1,000) the ground rod should suffice. If the wire is the right length to provide a low impedance (<1,000), you'll need a better counterpoise.

You might look here for ideas:

http://www.hamoperator/ah4/

Alan, KØBG
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WB6BYU
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Posts: 13125




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« Reply #8 on: July 14, 2003, 04:06:20 PM »

Your wire is over a half wavelength on 80m, and even
longer (in terms of wavelength) on the higher bands.
I would expect the input impedance to be high enough
that adding a lot more radials wouldn't make much
difference.

On 160m, though, the wire will be somewhat over a
quarter wavelength (making some assumptions about how
the wire is installed.)  You may find that adding some
radials will improve the efficiency on this band.

With a loaded quarter wave vertical, the radiation
resistance is often in the 20 - 30 ohm range, if not
lower.  Clearly, 10 ohms of ground loss will make a big
difference in efficiency.  But when the tuner sees an
antenna input impedance of 200 or more, that 10 ohms
of ground loss is a relatively small percentage, so the
losses will be lower.
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