Radio Communication

Geoff Partridge

The Radio Spectrum

Radio Spectrum refers to the part of the electromagnetic spectrum corresponding to radio frequencies -

Radio Bands and Channels

The radio spectrum is divided into ‘bands’. A band is a small section of the spectrum of radio communication frequencies, in which channels are usually used or set aside for the same purpose.Each of these bands has a basic bandplan which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility of transmitters and receivers.

Radio Bands (1)Band Name Abbr Frequency and

wavelength in airExample uses

Tremendously low frequency

TLF <3 Hz>100,000 km

Natural and man-made electromagnetic noise

Extremely low frequency

ELF 3 - 30 Hz100,000 km – 10,000 km

Communication with submarines

Super low frequency

SLF 30 - 300 Hz10,000 km – 1000 km

Communication with submarines

Ultra low frequency ULF 300 – 3,000 Hz (3 kHz)1000 km – 100 km

Submarine communication.Communication within mines

Very low frequency VLF 3 – 30 kHz100 km – 10 km

Navigation, time signals, submarine communication, wireless heart monitors, geophysics

Radio Bands (2)Band Name Abbr Frequency and

wavelength in airExample uses

Low frequency

LF 30 – 300 kHz10 km – 1 km

Navigation, time signals, AM long wave broadcasting , RFID, amateur radio

Medium frequency

MF 300 – 3000 kHz (3 MHz)1 km – 100 m

AM medium wave broadcasting, amateur radio, avalanche beacons

High frequency

HF 3 – 30 MHz100 m – 10 m

Shortwave broadcasts, citizens’ band radio, amateur radio, over-the –horizon communications, marine and mobile radio telephony

Very high frequency

VHF 30 – 300 MHz FM radio and television broadcasts, line of sight ground- to-aircraft and aircraft-to-aircraft, Land mobile and Maritime mobile, amateur radio, weather radio

Radio Bands (3)Band Name Abbr Frequency and

wavelength in airExample uses

Ultra high frequency

UHF 300 – 3,000 MHz (3 GHz)1 m – 100 mm

Television broadcasts, microwave devices/communications, radio astronomy, mobile phones, wireless LAN, Bluetooth, GPS and two-way radios

Super high frequency

SHF 3 – 30 GHz100 mm – 10 mm

Radio astronomy, microwave devices/communications, wireless LAN, most modern radars, communications satellites, satellite television broadcasting

Extremely high frequency

EHF 30 – 300 GHz10 mm – 1 mm

Radio astronomy, high-frequency microwave radio relay

Terahertz or Tremendously high frequency

THz or THF

300 – 3,000 GHz (3THz)1 mm – 100 µm

Terahertz imaging – a potential replacement for X-rays in some medical applications, terahertz computing/communications

Personal Experience• HF radio communications control in Hong Kong (part of the

Defence Communication Network) – 27 Sig Regt.• Mainly Telegraphic communication over HF radio (Long Haul)• Connections to Singapore, Gan (Indian Ocean), Cyprus, Brunei• Role was to monitor received signal quality and to request

frequency changes to ensure a high availability of the communication links.

• Transmitters and Receivers located on Stonecutters Island and The Peak (maintained by RN and C&W)

• 24/7 operation but great views of the harbour and Kowloon.

HF CommunicationsPropagation characteristics

Shortwave radio frequency energy is capable of reaching any location on the Earth as it can be refracted back to the earth by the ionosphere, (a phenomenon known as "skywave propagation").

HF CommunicationsPropagation characteristics

HF CommunicationsPropagation characteristics

• A typical phenomenon of shortwave propagation is the occurrence of a skip zone where reception fails. With a fixed working frequency, large changes in ionospheric conditions may create skip zones at night.

Skip Zone

The Ionosphere

• The ionosphere is a part of the upper atmosphere, from about 85 km to 600 km altitude. It is ionized by solar radiation. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth

The Ionosphere

Effect of Ionosphere ChangesAs a result of the multi-layer structure of the ionosphere, propagation often simultaneously occurs on different paths, scattered by the E or F region and with different numbers of hops. Particularly for lower frequencies of the shortwave band, absorption of radio frequency energy in the lowest ionospheric layer, the D layer, may impose a serious limit due to collisions of electrons with neutral molecules, absorbing some of a radio frequency's energy and converting it to heat.

Predictions of skywave propagation depend on:• The distance from the transmitter to the target receiver.• Time of day. During the day, frequencies higher than approximately 12 MHz can travel longer

distances than lower ones. At night, this property is reversed.• With lower frequencies the dependence on the time of the day is mainly due to the lowest

ionospheric layer, the D Layer, forming only during the day when photons from the sun break up atoms into ions and free electrons.

• Season. During the winter months of the Northern or Southern hemispheres, the AM broadcast band tends to be more favorable because of longer hours of darkness.

• Solar flares produce a large increase in D region ionization so high, sometimes for periods of several minutes, all skywave propagation is non-existent.

Frequency Changing (QSY)Communication quality and reliability on HF is dependant on the frequency in use. Methods used to determine when to change frequency were – • Distortion Monitoring• Forecasting using frequency prediction charts (these were useful

for choosing a frequency but not reliable for timing when to change frequency)

• Over a period of several days an HF path may be expected to fail at roughly the same time.

With a number of other ‘new boys’ changed the culture from re-active to pro-active frequency changes leading to fewer and shorter outages.

Frequency Prediction Chart

Further Study

• The field of radio communication is so vast that this talk only covers a fragment.

• There is a wealth of information on Wikipedia and the internet.

• The research for this talk resulted in me finding a number of documents that added to my memory of my work in Hong Kong