[Antennas] How do you use an antenna tuner?

2002年3月11日 07:45:47 -0500 (Eastern Standard Time)

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Frank,=0D
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I would disagree on your comment...=0D
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"In fact, a tuner in this situation will not help and may=0D
degrade performance."=0D
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A tuner, even in a tuned system can be a good thing.=0D
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Being a tuned circuit, it helps eliminate harmonics and=0D
other spurious emissions, usually with little loss or=0D
other ill effects on the antenna system.=0D
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73,=0D
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Bill KA8VIT=0D
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-------Original Message-------=0D
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From: [email protected]=0D
Date: Sunday, March 10, 2002 09:31:41 PM=0D
To: Pat W=0D
Cc: [email protected]=0D
Subject: Re: [Antennas] How do you use an antenna tuner?=0D
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Yup, that is a good 2 cents worth and probably worth much=0D
more. Max current is an indication that power is being=0D
transferred to the antenna.=0D
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The thing that most amateurs don't understand is that in=0D
order to make an antenna work well ( any antenna ), you have=0D
to get power into it. That only happens when the=0D
transmitter AND the antenna is matched to the transmission=0D
line.=0D
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That is pretty easy to do if you use coax. Simply connect a=0D
50 ohm coaxial feedline to the transmitter, then connect the=0D
other end of the feedline to an antenna that matches to 50=0D
ohms. No need for a tuner here. In fact, a tuner in this=0D
situation will not help and may degrade performance.=0D
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Most novices start this way and have pretty good luck with=0D
simple, single band dipoles flat-topped at about half=0D
wavelength above ground.=0D
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The trouble begins when someone suggests using an antenna=0D
tuner to turn the single band dipole into a multiband=0D
system. The unsuspecting usually get a cheap transmatch or=0D
'line-flattener' and install it between the radio and the=0D
coax going to the antenna. Then they wonder why it does not=0D
work so well on all the other bands even though the swr is=0D
very low at the radio. They have a hard time understanding=0D
that their troubles are caused by the impedance mismatch at=0D
the point where the antenna attaches to the feedline. =0D
Antenna current meters don't help the mismatch and the=0D
transmatch at the radio does not help it either. Such a=0D
setup guarantees that the radio will deliver a maximum=0D
amount of power to the feedline but most of that power never=0D
gets to the antenna, it just heats the feedline because of=0D
the mismatch at the feedline to the antenna. =0D
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One solution is to install a remote tuner to match the=0D
feedline to the antenna. Another solution is run open wire=0D
line to a balanced tuner that will tune the feeders AND=0D
antenna as one balanced system. The third and best solution=0D
is to stay with the original single band system that works.=0D
Putting up a second single band system to cover an=0D
additional band is usually lots cheaper than getting an=0D
antenna tuner.=0D
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Lastly, consider this.....even with a decent all band=0D
system, you can only work one band at a time. With seperate=0D
single band antenna systems it is possible to work more than=0D
one band at a time if you have the radios to do so. Works=0D
well for contesting.=0D
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Frank Kamp=0D
K5DKZ=0D
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Pat W wrote:=0D
> =0D
> My 2 cents worth.=0D
> Tuners can tune things they really have no business=0D
> tuning in the first place, and since a t-net tuner has=0D
> infinite settings for a match(only 1 being the correct=0D
> setting), it is difficult to know when the tuner is=0D
> doing any good.=0D
> THe simplest method for tuning(from Walt Maxwell's=0D
> 'Reflections') is to add a current sensing indicator on=0D
> the ouput side of the tuner. This is a very simple=0D
> device consisting of small powdered iron toroid(eg,=0D
> T50-2), a germanium diode, capacitor, 50k ohm carbon=0D
> potentiometer, and a good meter. The antenna center=0D
> output is wound 1 turn thru the toroid, and about 20=0D
> turns of small diameter wire is wound for the=0D
> secondary. Tuning for maximum output on the meter is=0D
> all that is required. WHen the tuner settings are at=0D
> their optimum, the meter is showing the most antenna=0D
> current.=0D
> =0D
> Without an output indicator, tuning in receive mode=0D
> for maximum received signal will indicate optimum=0D
> setting also.=0D
> =0D
> Pat W0OPW=0D
> =0D
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