TV Antenna Basics

Australian TV Channels - Analogue & Digital

Hertz (Hz) means cycles per second. (Heinrich Hertz was the first to build a radio transmitter and receiver while understanding what he was doing.) KHz means 1000 Hertz, MHz means 1,000,000 Hertz, and GHz means 1,000,000,000 Hertz

A TV channel in Australia will always occupy 7 MHz of this spectrum.
Any of these channels could contain either an analog channel or a digital channel.

Channels 0 – 12 are VHF channels.
Channels 28 – 69 are UHF channels.

The wavelength of a radio wave is: λ = 300/F where F is the frequency in mega-Hertz and λ is the wavelength in meters. Antenna elements are typically about a half-wavelength long.

Decibels

Decibels (dB) are commonly used to describe gain or loss in circuits. The number of decibels is found from:
Gain in dB = 10*log (gain factor) or
Decibel graph

In some situations this is more complicated than using gain or loss factors. But in many situations, decibels are simpler. For example, suppose 3m of cable loses 1 dB of signal. To figure the loss in a longer cable, just add 1 dB for every 3m. In general, decibels let you add or subtract instead of multiply or divide. There are some special numbers you might want to memorize:

20 dB	= gain factor of 100
10 dB	= gain factor of 10
3 dB	= gain factor of 2 (actually 1.995)
0 dB	= no gain or loss
-1 dB	= a 20% loss of signal
-3 dB	= a 50% loss of signal
-10 dB	= a 90% loss of signal

(Decibels can be used to describe changes in voltage. But this website will use them only to describe changes in power.)

Noise

Whether a signal is receivable is determined by the signal to noise ratio (S/N). For TVs there are two main sources (classes) of noise:

Atmosphere noise. There are many types of sources for this noise. A light switch creates a radio wave every time it opens or closes. Motors in some appliances produce nasty RF (radio frequency) noise.
Receiver noise. Most of this noise comes from the first transistor the antenna is attached to. Some receivers are quieter than others.

Receiver noise dominates on the VHF and UHF bands, and atmospheric noise is usually insignificant. On an analog channel, noise looks like snow. If there were only a barely perceptible amount of snow, this would correspond to how noise-free a DTV signal must be for a DTV receiver to lock-on to it.

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