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Leon
New member
Username: Leon
Post Number: 7
Registered: 4-2013
| | Posted on Saturday, June 15, 2013 - 10:16 pm: | 
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is a antenna tuner a must? how much do they help? |
Starface
Senior Member
Username: Starface
Post Number: 3249
Registered: 1-2005
| | Posted on Tuesday, June 18, 2013 - 6:21 pm: |
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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 laod 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.
Much 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.
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!
Now Let's learn how to "tune" that "tuner"
Most antenna tuners have an inductance rotary switch and two capacitors. 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 with low 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 swr 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!
73 George KI4NBE
George
KI4NBE
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Alsworld
Senior Member
Username: Alsworld
Post Number: 1036
Registered: 1-2002
| | Posted on Tuesday, June 18, 2013 - 8:10 pm: |
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If you have an antenna tuned to the frequency you will be talking on then no, no tuner required. An example, an Antron 99 tunes to the CB frequencies. An SWR meter really does help to get the antenna tuned properly though. I recommend that for sure.
Alan |
Tech237
Moderator
Username: Tech237
Post Number: 1685
Registered: 4-2004
| | Posted on Friday, June 21, 2013 - 9:12 am: |
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The thing that bot the above replies missed on, is an ATU can also be useful in limiting unwanted signals.
The output stage of most ATUs acts as a filter at the frequency it is set to, which attenuators signals outside of a fairly narrow range of requencies. Hence reducing, if not eliminating unwanted signals.
My recommendations, unless the antenna design (G5RV for example) dictates the need for an ATU, try to set the antenna up so that it does not needing one, then use a Low Pass filter to kill harmonics.
If an antenna designed for one range of frequencies, will not tune at that range, you have a BIG problem, that and ATU will only mask not fix - bad ground for example.
Tech237
N7AUS
God made me an athiest, who are you to question his wisdom?
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