Transcript Radio Communication

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 air
Example uses
Tremendously low
frequency
TLF
<3 Hz
>100,000 km
Natural and man-made
electromagnetic noise
Extremely low
frequency
ELF
3 - 30 Hz
100,000 km – 10,000 km
Communication with
submarines
Super low
frequency
SLF
30 - 300 Hz
10,000 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
3 – 30 kHz
100 km – 10 km
Navigation, time signals,
submarine communication,
wireless heart monitors,
geophysics
VLF
Radio Bands (2)
Band Name
Abbr
Frequency and
wavelength in air
Example uses
Low
frequency
LF
30 – 300 kHz
10 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 MHz
100 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 air
Example 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 GHz
100 mm – 10 mm
Radio astronomy, microwave
devices/communications, wireless
LAN, most modern radars,
communications satellites, satellite
television broadcasting
Extremely high EHF
frequency
30 – 300 GHz
10 mm – 1 mm
Radio astronomy, high-frequency
microwave radio relay
Terahertz or
THz
Tremendously or
high frequency 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").
HF Communications
Propagation characteristics
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
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 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:
• 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