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How to Use an Antenna
Tuner Get maximum power to
your antenna by learning how to hook up and use a tunner to
properly "trick" your rig!

Yes, "TRICK" YOUR
RIG! WHAT IS AN ANTENNA
TUNNER?
You have to learn how to hook them up to your tranceiver
properly and tune them correctly to make your radio
think that it is
feeding it's signal into a "perfect or near perfect 50 ohm load
called your antenna. An antenna tuner, (transmatch),
doesn't really TUNE your antenna OR ANY PART OF
IT!
What an antenna tuner or transmatch does do, however, is
transform the impedance at the antenna feed output at the radio to a
value that your transceiver can handle, (typically 50 Ohms). When
thinking about antenna tuners and SWR, it's important to remember
that the tuner has no effect whatsoever
on the SWR between itself and the antenna. It's the SWR between the transmitter and the tuner that is
changed with the tuner controls.
In layman's terms, all a
tuner does is act as a kind of adjustable impedance transformer
between the radio and the antenna. It takes whatever impedance the
antenna system presents, up to the design limits of the tuner, and
attempts to convert it back to 50 Ohms--or something reasonably
close to that value for the transceiver. When the transceiver "sees"
a 50 Ohm impedance, it is able to load or produce it's maximum
designed RF output into the system because it is designed to operate
into a 50 ohm load. Your
rig "thinks" it's seeing a 50 ohm antenna on it's
output! That power is transferred through
the antenna tuner, to the feed line and, ultimately, to the
antenna--minus any losses incurred along the
way. If you have high loses and a poor excuse for an antenna,
you will have a poor excuse for a good signal no matter how well
your tuner "tricks" your radio. Most of the power will be lost as
heat in the tuner and very little will get to the other
station!
These losses are the reason that the highest efficiency
feed-line for each individual case is desirable and why some
amateurs use ladder line on HF, which has the least loss per foot,
which means maximum power at the input terminals of the
antenna.
HOW TO HOOK UP AND
USE So now that you have a better understanding of what an
antenna "tuner" actually does, let's hook one up in a typical HF
station.
In the block diagram below we have typical Hf
station setup consisting of:
An HF Transceiver A Linear or
power amp Low Pass Filter Swr/Watt Meter combo The Antenna
Tuner A Dummy Load The MOST IMPORTANT PART......THE
ANTENNA!

Take a look at the block
diagram above and notice where the antenna tuner and SWR meter are
in relation to the flow of the RF signal coming from the
transceiver.
PLEASE DISREGARD THE LINEAR AND LOW PASS
FILTER FOR THE MOMENT! (Your station may not use
them) You
will notice that.... first, from left to right, you have the
transceiver, Swr/watt meter, ANTENNA TUNER and then the antenna on
the output. The rf moves from the transceiver to the SWR/WATT
meter, then finally thru the "tuner" and out to the
antenna. You just learned how to
hook it all up! Just remember that our goal is to make the
transceiver think all is well, and in order to "read" the SWR and
Power out pertaining to "all is well"......at the radio's
output....the meter must be between the radio
and the tuner. NOT ON THE ANTENNA
SIDE!
NOW LET'S LEARN TO TUNE THAT
TUNER!
Most antenna tuners have an inductance rotary switch
and two capacitors. (refer to photo at top of page) The capacitors
are often labeled ANTENNA and TRANSMITTER. In some antenna tuners
the inductance switch is replaced with a continuously variable
inductance, popularly known as a roller inductor.
Let's assume you're
using a tuner with an inductance switch, because they are the most
common.
SHOCK HAZARD! NEVER TRANSMIT
WITH THE TUNER COVER OFF AS IN THE NEXT STEP! TURN OFF THE POWER
TO THE RADIO!
Place both capacitor controls
at their mid-range positions. Don't trust the knob markers if this
is your first experience with the tuner! If you are
comfortable with the next procedure, remove the cover of the tuner
and turn the knobs until the moving capacitor plates are only half
meshed with the stationary plates. If the knobs are pointing to half
scale with the reference markings on the knobs and front cover,
consider yourself lucky. If not, loosen their Allen screws and
rotate the knobs so that they point to mid scale. Re-tighten the
knobs, replace the tuner cover and you're ready to go.
Turn the radio on and tune receiver to an
un-used frequency on the band you desire, listen for a few seconds, with
the antenna and transmitter controls at mid scale, move the
inductance switch to each of it's positions until you hear the
loudest noise or signals coming into your radio. Then, rotate the
antenna and transmitter controls until you get to the absolutely
loudest noise or signal level on the radio. All three of these
controls interact with each other so practice on several bands to
get the "feel" of the procedure. Select your final band of
operation and repeat the procedure above. When noise peaks out using
your ears and the S meter, your tuner settings should be very close
for final operation.With your rig set to low power monitor the
frequency to assure that it is not in use, send your ID then
transmit a continuous carrier while you tweak the antenna and
transmitter controls for the lowest reflected power reading with the
highest output power as read on the Swr/Watt meter. You may find
that you have to vary the position of the inductance switch a
position or two either way to get your best match. Play it safe
and un-key before turning the inductor switch...un-key
first....turn the switch...key up....repeat as needed until
lowest SWR and maximum output. Be gentle to your radio; keep the
key-down periods as short as possible. Depending on the impedance at
the antenna input (and the overall design of the tuner) you may not
be able to obtain a flat 1:1 SWR on all frequencies and
bands. Also important to remember is that your Swr will change,
go up, as you tune further away from the frequency you used to
"trick" your radio! So re-check and re-tune as needed as you move
around the band. You can get an idea of your SWR bandwidth by
starting with your original frequency, and using the procedures
above withlow power, (don't move any knobs or switches after best
setting)....sweep or tune your VFO up and down the band while
watching the SWR readings and note the frequency where the SWR
reaches 2:1 at the higest and lowest frequency. Stop
there!
Example:
If your on
40 meters at say...7.262mhz as your starting point, and your SWR is
2:1 at 7.292mhz and the highest going the other way is 2:1 at
7.259mhz, then your "safe tuning range" without retuning the antenna
tuner would be about 60khz. Keep in mind to use very low power
and ID because your signal may be heard for a split second as you
tune across the band! When that transmit key is down, someone
somewhere can hear you. Even a dummy load gets out
somewhere! Remember your "TRICKING" your way around a good
antenna! ++++++++++++++++++
Editors
note:
In reality, there is no "tricking" and we
were playing with words here like "tricking, fooling", etc. It
is useful to employ a matching device, the antenna tuner, between
the transmitter and the antenna feeder when antennas with complex
impedances are used..... so the transmitter will "see" a 50 -52 ohm
load even though a significant mismatch is present at the
antenna feed point. The tuner, matchbox or transmatch as it is
sometimes called, will not correct the actual SWR condition on the
feed line OR antenna, but it will resonate the antenna system
as a whole and allow the transmitter to
deliver as much power to the antenna system as possible
within the design parameters of the tuner. The transmitter now can
produce it's rated power out to the tuner in the
hopes that the tuner can do it's job and get most of that power into
the antenna system with some efficiency. Bottom
line: Your transmitter will not
know that you are trying to "load up" those old rusty bed springs or
that poor excuse for an antenna! Just
because you're now seeing that magic 1 to 1 VSWR reading on the
meter does not mean you have changed the design of those old rusty
bed springs you're trying to us as an antenna!!! The more efficient
your antenna system.....the
better!
POWERED BY HAM
RADIO!
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