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Author Topic: Tuning a manual antenna tuner  (Read 8714 times)
The Guru
Posts: 77

« on: January 21, 2014, 06:54:17 PM »

Tuning a manual antenna tuner:

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.
If not, loosen their Allen screws and rotate the knobs so that they point to mid scale.
Also zero the roller inductor if so equipped.
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 (or roll {turn} the inductor) 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 roll {turn} the inductor)  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 started with. 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! Then record the setting for future use as a starting point for each band. (Some manufactures of tuners publish inductor positions to start with for each band but this is only a guide and will change with each antenna)
Always recheck the SWR when you start transmitting or make any changes including increasing power and retune if necessary.

Bill VE3LFD   
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