Antenna Tuners (External Type)
Antenna Tuners (External Type)
They’re known as “transmatches”, “matchboxes”, or just “tuners”.
First – Do you really need an antenna tuner?
-Other solutions can be:
- Resonant antenna (Best for single band/specific frequency, but may require a bit of real estate).
- Trapped antenna (Good for multi-band use, but can be narrow-banded).
- Screwdriver-type antenna.
What a tuner can do for you:
-Widen the usable range of your current antenna (e.g.: Mobile Hamstick-type Whip).
-Allow you to used “balanced” feed line or a long/random wire (your coax is “unbalanced” feed line; almost all of today’s Ham radios are made to use unbalanced (coax) feed line).
- The tuner “matches” your radio to the different feed lines.
-Allow you to operate multiple bands on a single-band antennaas long as the antenna is a least a half wave long on the lowest band where you plan to operate (if using a balanced feed line).
- May help if you have limited real estate.
What a tuner doesn’t do:
-Doesn’t change the resonant freq of your antenna.
-Doesn’t really change the SWR on your antenna or feed line, only the SWR that your radio “sees”.
- Keeps your radio’s protection circuit from “folding back” the output power due to high SWR.
Feed lines:
-Feed line as an inductor/capacitor network.
-Can use coax (50 ohm), open wire (600 ohm); ladder line (450 ohm); or “twin lead” (like the old TV ribbon cable) (300 ohm).
-A serious mis-match in your feed line can cause excessive losses.
-Balanced feed lines can have very high SWR, but much lower loss than unbalanced (coax) cable.
-Tuner controls can allow for feed line inductance/capacitance to make the radio happy.
-Tuners use variable capacitors and inductors (tapped or roller inductors).
NOTE: Feed line can have so much loss depending on feed line type/size (usually measured in dB/100 feet; 3dB loss means half your power won’t make it to the antenna, 6dB loss means about 75% of the power won’t make it); but it will show a good SWR since the power is lost before it can be reflected back to be measured).
-If possible, check the SWR first at your antenna feed point before installing the feed line; then check at the shack end of the feed line.
-Consider balanced line for longer runs to the antenna.
Using your tuner:
Follow your tuner’s hookup instructions for balanced/unbalanced feeder or random/longwire.
Antenna should be at least a full half wave on the lowest band where you plan to operate.
General tuning technique (see your specific tuner’s manual):
-Set variable capacitors to midrange.
-Set inductor to max noise.
-Tune variable capacitors to max noise (may require multiple tries).
-Set radio to low power; transmit steady carrier (AM/FM or CW; be sure to ask QRL first); adjust capacitors in turn; readjust inductor and then capacitors as necessary.
- If you hear arcing (popping/cracking/buzzing) inside the tuner, stop. Your antenna may be too far off resonance on that particular freq for that particular tuner to handle.
- Try changing antenna and/or feed line length.
-If tuning was successful, increase your transmitter power and operate.
-An auto tuner at the antenna with coax ran from the station to the tuner is also an option.
