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 NameAbbrFrequency and wavelength in air Example uses Tremendously low frequency TLF<3 Hz >100,000 km Natural and man-made electromagnetic noise Extremely low frequency ELF Hz 100,000 km – 10,000 km Communication with submarines Super low frequency SLF Hz 10,000 km – 1000 km Communication with submarines Ultra low frequencyULF300 – 3,000 Hz (3 kHz) 1000 km – 100 km Submarine communication. Communication within mines Very low frequencyVLF3 – 30 kHz 100 km – 10 km Navigation, time signals, submarine communication, wireless heart monitors, geophysics

Radio Bands (2) Band NameAbbrFrequency and wavelength in air Example uses Low frequency LF30 – 300 kHz 10 km – 1 km Navigation, time signals, AM long wave broadcasting, RFID, amateur radio Medium frequency MF300 – 3000 kHz (3 MHz) 1 km – 100 m AM medium wave broadcasting, amateur radio, avalanche beacons High frequency HF3 – 30 MHz 100 m – 10 m Shortwave broadcasts, citizens’ band radio, amateur radio, over-the –horizon communications, marine and mobile radio telephony Very high frequency VHF30 – 300 MHzFM 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 NameAbbrFrequency and wavelength in air Example uses Ultra high frequency UHF300 – 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 SHF3 – 30 GHz 100 mm – 10 mm Radio astronomy, microwave devices/communications, wireless LAN, most modern radars, communications satellites, satellite television broadcasting Extremely high frequency EHF30 – 300 GHz 10 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 Communications Propagation 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"). refractedionosphereskywave

HF Communications Propagation 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

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 Earthionizedradio propagationEarth

The Ionosphere

Effect of Ionosphere Changes As 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:scatteredradio frequency 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.D Layer 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. Solar flares

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