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Author Topic: AH-4 Automatic antenna tuner and loops  (Read 315 times)
KC6UNM
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Posts: 6




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« on: January 17, 2007, 01:29:38 AM »

I'm thinking about trying one of these out with a large horizontal loop.  My question is this, since these are meant for "random" lengths of wire when a single long wire is used against a ground or counterpoise, does that apply when using them to tune a loop.  I've got 440ft of #12 wire and a big lot.  Should I throw up all 440ft (3/4 wave on 160 meters) or will this thing work better with say a full wavelength on 80 meters (280ft)?
Some of the reviews here on E-Ham have me confused with the way people say they are using these things.
Thanks for looking.

73
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SSB
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Posts: 1




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« Reply #1 on: January 17, 2007, 01:56:01 AM »

An L network is an L network.  I have been using an AH4 with small and large loops and the setup works very well.  An 80 foot perimeter loop will work 80 - 10 meters.

Alex....
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W5DXP
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« Reply #2 on: January 17, 2007, 07:00:03 AM »

A balanced antenna is designed for the the currents in the antenna to be balanced. When using an unbalanced autotuner at the feedpoint of a balanced antenna, the currents are not balanced. The coax braid is connected to one side of the balanced antenna while the coax inner conductor is connected through a phase-shifting network to the other side of the balanced antenna. Such may "work" for hams but is not good RF engineering practice.
--
73, Cecil, w5dxp.com
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K0BG
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« Reply #3 on: January 17, 2007, 07:10:42 AM »

It will work, maybe not as well as some other types of antennas, but the AH-4 won't care. The only thing to remember is, the packing nuts on the bottom of the AH-4 do not seal completely. Therefore, you should mount it in such a way so that rain and snow can't enter.

You might look here too: http://home.comcast.net/~hamlakemn//ah4/

Alan, KØBG
www.k0bg.com
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KT8K
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Posts: 1490




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« Reply #4 on: January 17, 2007, 07:43:33 AM »

The bigger the better, as the radiation angle will drop as the loop gets bigger (encloses more space).  See www.cebik.com where W4RNL has many excellent antenna articles, including some on horizontal loops.  

My experience with horizontal loops makes them my favorite choice for a nearly-omnidirectional all-band antenna, and my next one will include a tuner mounted at the feedpoint, or connected to the feedpoint by ladder line.

My last loop zigged and zagged a bit through tree branches, was only 20-25' above ground, and had a fundamental resonance around 5 mHz, but it worked very well, better on successively higher bands, and beat my vertical dipole all hollow on 10m.  I'm replacing the fan dipole I just lost in the ice storm with a horizontal loop!  (just as soon as the ice melts a bit)
73 & best rx de kt8k - Tim
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W5JI
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Posts: 146




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« Reply #5 on: January 17, 2007, 09:08:28 AM »

As K0BG and others have said.....it will work fine with your loop. I agree with one responder who said to make it as large as possible.

My addition to the responses is that you should use an isolator on the coax feedline at the tuner to prevent RF on the outside of the coax shield. This can simply be 6 to 10 turns of the coax feedline about 10 to 12 inches in diameter (don't make the diameter too small or the coax inner dielectric may flow and allow the center conductor to short to the shield) or it could be one of the ferrite bead isolators sold by balun vendors.

The reason for the isolator is that the tuner is basically an unbalanced tuner being used to tune a balanced antenna. That means the RF ground reference (the coax shield) is no longer a ground reference when it is connected to one end of the loop. You probably know this but, do not connect the tuner ground terminal to a ground rod as the manual indicates.......

73.....Jim  W5JI
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« Reply #6 on: January 17, 2007, 02:18:36 PM »

Hi Don, I have an AH-4 connected to a horizontal loop that has a total of 120' of wire and is in a triangular shape. It is about 20' high and is connected to my AH-4 via 20' of 450 ohm ladderline. One end of the ladderline goes to the top terminal and the other to the ground terminal of the AH-4.

I have power lines running along the back of my yard and the triangular loop is better because of this. I also wanted an antenna that was better for local use and this covers all the bands and is perfect for that. 73's and good luck with it.  Bill
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K3AN
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« Reply #7 on: January 17, 2007, 04:09:19 PM »

I posted this article a while back on the subject you're asking about.

http://www.eham.net/articles/14338
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KC6UNM
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Posts: 6




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« Reply #8 on: January 17, 2007, 07:46:03 PM »

Wow!!

Thank you all for the good info.  I ordered that AH-4 this evening.

For now I am planning to mount mine under the eave of the second story to give it some additional weather protection and it will feed the antenna directly from there.  Good advice on the coil balun...

Glad I asked.   Smiley

73
AD5ZC ex KC6UNM
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