Trying to tune antennas / 2016-03-31 - Koos van den Hout

2016-03-31 10 months ago
Besides the antennas for HF frequencies I also have an antenna tuner.

For my readers who aren't busy with radio: the combination of a transmitter and an antenna works best when the antenna acts as a resistor at the value the transmitter expects. In amateur radio most transmitters expect 50 ohms loads. But, the antenna only does that at the frequencies it is resonant on, on other frequencies it will act more like a coil or a capacitor and reflect power back to the radio. This is where an antenna tuner comes in which tries to adjust the antenna using coils and capacitors to match what the radio expects. The downside is you lose power in the tuner and the antenna itself is still not working at its optimum. But an antenna somewhat working is better than no working antenna at all.

So I am trying to use the antenna tuner to be able to transmit on frequencies other than the ones the antennas are made for. Sofar the results are for the 10/20/40m endfed antenna I built at the radio club:
  • 10 meter: native frequency
  • 12 meter: the tuner can fix it
  • 15 meter: the tuner can fix it but the returning signal is so large the radio starts acting weird
  • 17 meter: the tuner can fix it
  • 20 meter: native frequency
  • 30 meter: the tuner can fix it and I made contacts on that band
  • 40 meter: native frequency
And for the LW-10 antenna I bought last year hanging outside the attic window:
  • 6 meter: the tuner fixes it
  • 10 meter: works
  • 12 meter: fails to tune
  • 15 meter: fails to tune
  • 17 meter: the tuner can fix it but USB devices around my PC crash or misbehave
  • 20 meter: works
  • 30 meter: barely tunes
  • 40 meter: works
The antennas were both not to far from the ground and from the house so this can influence their behaviour.

The manual for the LW-10 antenna suggests that using its earth connection to earth it at the transformer box helps against noise. Adding a simple earth connection does not help tuning at 30 meter but it seems to reduce the returning RF problem at 17 meters.

Update: This article When is an Antenna Tuner not an Antenna Tuner? - DX Engineering has a better explanation of what the 'Antenna Tuner' does and why it should be called a 'transmitter matcher'.

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