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Author Topic: Multiband Dipole Antenna - TX with autotuner  (Read 881 times)
N3BSZ
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Posts: 58




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« on: October 21, 2010, 04:56:08 PM »

I am looking at upgrading my TS-430/ MFJ-962 pair to a transmitter with a built-in tuner.  The current setup has the MFJ tuner fed with ladder line.  The antenna is cut for 80 meters.

Will I be able to tune the antenna with a 4:1 balun using the built in tuner?

Will I get a lot of common mode currents inside the shack?

I am getting lazy.  I would rather build gear than tune/operate/tune...
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WB6BYU
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Posts: 13336




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« Reply #1 on: October 21, 2010, 05:49:33 PM »

The built-in auto-tuner in most rigs will have trouble matching the range of impedances encountered with such an
antenna.  You MIGHT get lucky with just the right feedline length, or you can switch in different pieces of feedline
to get lengths that the auto-tuner will match on all bands.  A lot depends on the matching range of the particular
tuner.
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WE1X
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Posts: 338




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« Reply #2 on: October 23, 2010, 08:04:44 AM »

Tom,

As the previous post stated, you may get away with it. However, depending upon your setup it may not be terribly efficient and may pose more problems than the expected convenience. Another alternative would be to run your ladder line to a remote antenna tuner (e.g., SGC, Icom AH-1, etc.) the coax to the shack. This should be more efficient and just as convenient without the matching headaches, losses and possible rig damage (due to various impedances while the internal tuner is seeking a match) associated with internal tuners.

harry we1x
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G0GQK
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Posts: 634




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« Reply #3 on: October 23, 2010, 01:56:43 PM »

The internal tuner in tranceivers should be regarded as trimmers to be used with an antenna which is almost resonant. Using an 80 metres dipole as a multiband antenna involves some very high resistances which only an external ATU can successsfully bring into resonance. There is a possibility that expensive damage could be caused to an internal ATU. Not only that, most users of internal ATU's are unaware that there is a reduction of radiated power, a 100 watts can be reduced to 85 watts.

G0GQK
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N0AZZ
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Posts: 241




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« Reply #4 on: October 24, 2010, 07:12:56 AM »

Internal tuners in radios will for the most part only tune to about 3:1 that's it.
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