Can someone explain to me in laymans terms what exactly an antenna tuner does?

Question

So, theoretically, if I had a 1/4 wave antenna cut for 144MHz, could I use an antenna tuner to just "tune" it to get a close SWR to 151MHz?

Answer 1

Yes but you will have some losses. If you can live with the loss then who cares. The tuner adds passive components to the antenna height to make it "think" it is tuned to that frequency. This is common practise. Once again it depends on your application and how much gain you want. But doing it is very common. Take short wave radio enthusiasts for example. They don't put up ten antennas. Some put up more than one, but, not ten. Then they tune it.

Answer 2

The ATU can present a 50 ohm load (VSWR=1) to the transmitter, but a 144 mhz antenna will not radiate the same as a 151 mhz antenna. in the vertical orientation, the extra length of the 144 mhz antenna will cause the major lobe of radiation to lift above the horizon. This may be benefitial in receiving Aircraft in flight, but will significantly reduce the reception from ground based vehicles. The prefered solution would be to reduce the physical length of the 144 mhz antenna to be closer to resonence at 151 mhz.

Answer 3

It basically matches a tranceiver to a load which is otherwise mismatched, which you get mismatch when you don't use a proper antenna for example.  The performance won't be as good as if you had a proper antenna for 151 MHz due to incurred losses. So you could get to 151 Mhz with 144 Mhz antenna.  But the tuner doesn't change the resonant frequency of the antenna, merely tricks it by adjusting the loads.