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Author Topic: Automatic Antenna Tuners and Dipole Antennas  (Read 789 times)
KD2FAH
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« on: January 02, 2003, 11:29:19 AM »

I just purchased a Kenwood TS-440AT. I have a 10 meter 1/2-wave dipole antenna that I would look to hook the rig up to but heard that it is not recommend if a rig has a built in automatic antenna tuner. Is this fact or fiction?
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W8AD
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« Reply #1 on: January 02, 2003, 11:40:48 AM »


Not true--an auto tuner will work great your 10 meter dipole. The advantage of using your auto tuner is that it will help to "broaden out" your 2:1 SWR bandwidth and allow you to use more frequencies across 10 meters with lower SWR. Hams use internal and external autotuners with dipoles all the time. It won't make a poor antenna/installation a good one, but it'll sure help.

Have fun,  Don,  W8AD
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K5DVW
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« Reply #2 on: January 02, 2003, 11:53:59 AM »

It might be good to know what kind of antenna you have and what kind of power it's rated for. It's possible that with higher feedline SWR the antenna won't be able to handle the rated power. So, if you use an auto tuner and operate the antenna out of its design parameters, you could damage the match or traps (if it has any).

The solution would be to use much less than rated power when the untuned SWR is greater than 2:1

K5DVW
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AC5E
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« Reply #3 on: January 02, 2003, 12:16:20 PM »

Well, both dipoles and automatic antenna tuners are large subjects.

To be as brief as possible, a typical resonant dipole SHOULD have a feedpoint SWR of less than 3:1 across the band it's cut for. Feedline losses will make indicated SWR somewhat less at the antenna tuner. Most built in tuners are good for SWR's of less than 3:1. So the built in tuner in your rig should work very well.

However, trying to use a dipole on a band it's not cut for is another matter. Except for 15 Meters on a 40 Meter dipole, in most cases the feedpoint VSWR is essentially infinite - far beyond the range of any remote tuner.

Even with feedline losses that reduce indicated SWR to 10:1 or less, most built in tuners and very few accessory tuners will actually match anything but themselves under those circumstances.

73  Pete Allen  AC5E
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W9WHE
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« Reply #4 on: January 02, 2003, 12:16:45 PM »

Use your 10 meter dipole FOR 10 METERS, the tuner will broaden out the useable bandwith. If you hear me, please give me a call!

HOWEVER, your 10 meter dipole is too short to be used to transmit on any frequency lower than 10 meters. If you want to transmit on other bands, you will need to either add traps, or connect additional dipoles to your feeder (in paralell).

Also, are you using a Balun at the feed point?  You should.
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KD2FAH
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« Reply #5 on: January 02, 2003, 01:14:36 PM »

Exactly my point is to use my home-brew 1/2-wave dipole (it does not have any traps) exclusively for 10-meter. I am not looking to work out of the band or hoping that the auto-tuner will allow me too. I am just looking to use this wire antenna temporarily until the weather breaks and I can install a new veritcal.
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W4YA
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« Reply #6 on: January 02, 2003, 06:08:42 PM »

My TS-440 is over 13 years old and works fine on 10. Don't forget that you can bypass the internal tuner if you want to with the AUTO/THRU button, but you don't have to. Enjoy it!!!
73, Jim W4YA
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