Many people thinkthat there is no need to change an existing TV antenna in order to pick up digital TV broadcasts. In some cases, your old antenna may do the job.

In most cases though, you will be better off with a completely new antenna installation, with an antenna selected to suit the digital broadcasts for your area.

First, let’s look at the situation where your existing antenna is a VHF Yagi, log periodic or other antenna type such as a phased array. Most likely, this will be sized to cover all the channels in the VHF band, including channel 0. In other words, it will be a large and ugly structure of aluminium tubing that the local bird life has enjoyed for years.

And while this may have done sterling service for the analog channels, the fact that it is large enough to cover channels 0-5 will be a distinct drawback when analog TV broadcasts cease at the end of 2009.

Why? Because the antenna will continue to pick up all manner of extraneous signals which can interfere with digital TV reception, including high-power AM & FM radio transmissions and interference from power lines. The simple fact is that digital TV broadcasts in the VHF band are only on channels 6-12.

So your large VHF array is still an antenna but now it also picks up signals that you don’t want!

VHF digital antennas
are smaller

A new VHF antenna for the digital channels will be much smaller (because it doesn’t have to get down to channels 0 and 2) and less obtrusive. Not only that, because it does not have to cover such a wide frequency range, it will more than likely have slightly more gain than your previous analog antenna.

Fig.1: the digital cliff, represented by the blue line, shows how too little or too much signal results in a "no signal" message on your TV screen. For analog (the red line) there will always be something on the screen, even if it is only snow.

Perhaps even more importantly, there are some areas of Australia where digital television will only be transmitted on UHF. No VHF antenna will receive UHF properly, despite the anecdotes from "a mate who knows someone" who receives a marvellous UHF picture from the antenna they erected in 1956 . . .

Table 1 shows the wanted channels on the VHF and UHF bands for digital TV in both Australia and New Zealand.

We will discuss the UHF TV bands later in this article. For the moment, let us compare analog and digital signals and how they perform with varying signal strength.