VHF and UHF¶

Frequency range:¶

The carrier is sinusoidal signal used to transport (carry) voice/data through space (air).

The carrier itself contains no information.

Information is added by modifying one of the carrier's parameter:

Note:

$$ c = f \lambda $$

Where:

An antenna is efficient when it's length is comparable to a fraction of the wavelength - typically λ/4)

VHF:

FM broadcast radio: 88-108MHz, let's say carrier is 100MHz

$$ \lambda = \frac{3 \times 10^{8}}{100 \times 10^{6}} $$

$$ \lambda = 3 \text{ meters} $$

So, with λ/4 'rule', the antenna should be:

$$ \lambda/4 = 0.75 \text{ meters} $$

Trust me I'm stupid:

Human Voice transmitted without modulation - 1kHz:

$$ \lambda = \frac{3 \times 10^{8}}{100 \times 10^{3}} $$

$$ \lambda = 300,000 \text{meters} $$

Antenna would be:

$$ \lambda/4 = 75 \text{ km} $$

The modulating signal (here analog) is combined with carrier signal to produce modulated signal:

Amplitude Modulation

Used in VHF and UHF Communications:

The modulating signal (here analog) is combined with carrier signal to produce modulated signal:

Frequency Modulation

The modulatin signal - DIGITAL - is combined with carrier signal to produce modulated signal:

ASK

MISSING :(

FFT of Carrier signal, AM Modulated signal, and FM Modulated signal

The modulated signal creates sidebands around the carrier frequency: the bandwidth increase.

In VHF/UHF, using FM for Voice Communications, Typical bandwidth is 12.5 kHz (narrowband) or 25 kHz (wideband) per channel.

If you have a 1 MHz frequency range - around the carrier frequency: