Aerial Tuning Units

The piece about co-ax above was written by Bill Shearman, former Head of Electronic Warfare at RACAL so we won’t argue with him.

Whether receiving or transmitting, it’s all about energy transfer. For us listeners, all we want to do is get whatever signal the passing wave has deposited on our aerial element, wire, beam or rod at whatever impedance transferred to an impedance our radio will like.

Do that and losses are less, reception is better and with an ATU, you get a bit of free gain. And they are passive, no electronic gain to offer noise and get overloaded by the local AM station.

In fact, an ATU will pre-select the range of frequencies you want to hear and by default reject the rest. This can improve signal-to-noise ratio, so improving your perception of the signal you want to hear.

A modern radio passes a band of frequencies (BPF) for processing. In that band, signals large and small appear. The ratio between them can be 1,000,000 : 1 or greater, the small stuff getting lost in the shadow of the greater.

Use the preselection of an ATU to narrow the band and the radio stands a better chance. So why aren’t we all using them?

Our picture show the simplest pi-tank but they come in all sorts of configurations. In short, if you are serious about SWL, get an ATU.