Amateur Radio Foundation Licence Presentation. HAM COLLEGE. Produced by. Neil Husk VK6BDO. There are nine sections in the syllabus:. Nature of Amateur Radio. Licence Conditions. Technical basics. Transmitters and Receivers. Transmission lines and Antennas. Propagation. Interference.
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Nature of Amateur Radio.
Transmitters and Receivers
Transmission lines and Antennas
Operating practices and Procedures
The written exam consists of 25 multi choice type questions which are to be completed in 30 minutes.
With the exam paper is an information sheet which will contain formula, graphs, charts and diagrams to assist you in answering the questions.
You must obtain 70% (18 correct) to pass the theory and progress to the practical
The practical exam includes several oral questions and will require you to do several demonstrations.
Amateur radio is intended to facilitate the hobby of radio communications.
Amateur radio as a hobby has many aspects:
And many more
Amateur radio activities are authorised under an amateur licence.
Other forms of licences authorise other types of radio communication such as
Citizens Band (CB);
Point to Point links;
Operation of an amateur station is subject to the conditions in the:
Radiocommunications Act 1992
Radiocommunications Regulations 1993
Radiocommunications Licence Conditions (Amateur Licence) Determination No1 of 1997
Radiocommunications Licence Conditions (Apparatus Licence) Determination 2003 (as amended)
The latest amendment was released in 2005.
The Amateur Service operates on frequency bands allocated for Amateur use.
Other services such as broadcasting, aeronautical and maritime are allocated their own frequency bands.
The amateur service shares some frequency bands with other services
The allocated bands are laid down in the LCD
An Amateur Licence primarily authorises the operation of an amateur station for:
Self training in radio communications;
Intercommunications between amateurs
Technical investigations into radio communications
Except in a distress or emergency situation the amateur licence only authorises amateur to amateur communications.
A Radio Inspector may authorise out of band operations for a specific reason.
Amateurs may transmit messages on behalf of a third party with in Australia provided it is not for gain, commercial purposes, an advertisement or entertainment.
Third party messages to other countries depends on that countries (the other country) laws.
Distress signals are used where “imminent danger exists to human life”
Distress communications are indicated by the use of the word ‘Mayday’.
Distress communications have priority over all other communications.
Any person hearing a ‘Mayday’ communication are responsible for passing the information to an appropriate authority.
Urgency signals are used where human life is not in imminent danger but assistance is urgently required.
Urgency signals are indicated by the use of ‘Pan Pan’
Urgency signals receive priority of all communications except distress signals.
Urgency signals should be reported to an appropriate authority.
An amateur licence allows the holder to transmit on:
A. Marine Bands
B. Aeronautical Bands
C. Amateur Bands
D. Any HF Band
ANSWER: C - Amateur Bands
Amateur radio is intended to facilitate:
A. Commercial gain in radio communications
B. A way of saving on phone bills
C. A way of using unwanted commercial radio equipment
D. A hobby in radio communications
ANSWER: D - A hobby in radio communications
You hear an urgency message, you should:
A. Switch off your radio
B. Tell everyone on the frequency
C. Ring emergency services
D. Give the message priority
ANSWER: D - Give the message priority
Australian amateur call signs consist of two letters, followed by one numeral and two, three or four letters.
VK6NT VK6KTS VK6FNBX
Australian call signs normally commence with the letters ‘VK’.
This is an international allocation to Australia.
Other allocations which may be issued to Aust amateurs are ‘VI and ‘AX’.
These are only issued for special events on a temporary basis.
p 58, 69-70
The numeral identifies the State or Territory in which the amateur is licensed to operate.
1 Australian Capital Territory
2 New south Wales
5 South Australia
6 Western Australia
8 Northern Territory
9 External Territories
The remaining two, three or four letters identify the type of licence held by the operator.
Any two letter suffix, or three letter suffix that begin with A, B, C, D, E, F, G, J, K, T, U, W, X, Y & Z indicate an advanced licence.
A three letter suffix beginning with H, L, M, N, P & V indicate a Standard licence.
Four letter suffix’s are Foundation licences.
Three letter suffix beginning with R are repeaters or beacons.
The correct identification for an amateur station is the call sign allocated to that station.
Station identification must be transmitted at the beginning of a transmission or series of transmissions, at least every ten minutes during the series of transmissions and at the end of the series.
A series of transmissions is a continual conversation between two or more stations.
Any transmission must be contain station identification.
Three letter groups commencing with Q were originally introduced to shorten commonly used phrases particularly when using morse code.
They can be used to clarify common messages when conditions are not good or there is a language difficulty.
When using voice communications under good conditions it is not necessary to use Q codes.
As foundation licensees you are not required to know any of the Q code but do need a knowledge of what it is for.
The transmission of secret coded or encrypted messages is generally not permitted.
The only allowable use of coded or encrypted signals is for the control of satellites, repeaters, beacons etc.
p 55, 58
The transmission of any form of entertainment is not permitted.
An amateur station may not be used for commercial gain.
An amateur station may not be used to advertise any item or service.
Subjects on which many people have very strong opinions can easily cause heated arguments or can cause individual offence, such as Religion, Politics or Sex should be avoided.
An amateur call sign VK2BH would belong to:
A. An American licensed technician in Boston
B. An Australian licensed amateur in NSW
C. A foreign amateur operating in Australia
D. An Amateur licensed in Venezuela
ANSWER: B - An Australian amateur in NSW
All amateur transmissions must include:
A. Your name
B. Your location
C. The power being used
D. Your call sign
ANSWER: D - Your Call sign
An amateur must produce their licence for:
A. Anyone who asks for it
B. Local government inspectors
C. ACMA inspectors
D. A person claiming interference from your station
ANSWER: C - ACMA inspectors
Before looking at the actual procedures,
Radio telephony is voice and radiotelegraphy is morse code.
Before transmitting always listen to ensure you will not interfere with another transmission already in progress.
Remember that you may not be able to hear both sides of another conversation.
If in doubt – ask “is the frequency in use”.
Avoid using Slang or big words.
Remember you never know who listening.
p 60, 61
Radio telephony is voice and radio telegraphy is morse code.
The call in telephony consists of:
The call sign of the called station not more than three times;
The words “This is”;
The call sign of the calling station not more than three times
The word “Over”
VK6KTS VK6KTS VK6KTS THIS IS VK6BDO VK6BDO VK6BDO OVER
A general call to any station may be made by substituting the signal ‘CQ’ for the called station.
CQ CQ CQ THIS IS VK6BDO VK6BDO VK6BDO OVER
On certain occasions a station may modify a CQ call with an additional designation.
CQ DX - calling CQ but wants a distant station.
CQ JOTA - Any JOTA station.
CQ Contest - Any contest station
A reply to a call should consist of:
The call sign of the calling station not more than three times;
The words “This is”
The call sign of the replying station not more than three times
The word “Over”
VK6BDO VK6BDO VK6BDO THIS IS VK6KTS VK6KTS VK6KTS OVER
Each grade of amateur licence allows the use of different frequency bands and emission modes that may be used on each band.
The permitted frequency bands and the modes permitted on that band, for each grade of licence are shown in the LCD.
p 59 & LCD
The Amateur Foundation Licence allows a maximum power output of 10 Watts when using Single Side Band (SSB), Amplitude Modulation (AM), Frequency Modulation (FM) or Carrier Wave (CW) emissions.
The Foundation Licence only authorises the use of unmodified, commercially manufactured transmitting equipment.
The Foundation licensee must not make any modifications to any amateur radio transmitting equipment.
A licensee must not operate a Amateur station if operation causes harmful interference to other radio services.
The ACMA has the right to restricted the operation of an amateur station to avoid interference.
ACMA inspectors have the right to require an amateur to produce his/her licence.
ACMA inspectors have the right to inspect stations.
Inspectors also have the right to confiscate any unlawful equipment or equipment that is capable of being used in an unlawful manner.
p 58 & Radio Regs
An amateur licence is issued to operate from a specific address.
The ACMA must be notified of any permanent change of address within 7 days of the change.
Operation from a temporary address may be continued for up to four months.
A Foundation licensee may authorise a suitably Qualified person to operate the licensee’s Amateur Station.
To operate a station is to control the transmitting equipment.
A qualified person is a person who has a certificate of proficiency – not necessarily a licence.
You can only authorised a person to your licence level.
Do Not Confuse this with Authorised Station Use
To operate a station is to control the transmitting equipment.
If the licensee is in control of the station anyone may use the microphone and talk.
You may also pass messages, within Australia, for a person other than the amateur you are talking to.
This is termed “Third Party Traffic”
Other countries may not allow this and it is subject to the other countries laws.
Foundation licence holders must use equipment that is:
A. A specified brand.
B. Unmodified transmitting equipment
C. Modified transmitting equipment
D. Second hand equipment
ANSWER: B. Unmodified transmitting equipment
A message on behalf of a third party is subject to:
A. The number of words
B. Where the third party is located
C. OK on some frequencies
D. Regulatory Conditions
ANSWER: D. Regulatory Conditions
Specified bands and emissions for amateur operators are contained in:
A. Transceiver user manuals
B. Amateur radio journals
C. Foundation manual
D. Licence conditions determination
ANSWER: D Licence Conditions Determination
The universe is made up of matter.
All matter is made up of atoms
Atoms consist of charged particles called protons, neutrons and electrons.
Protons have a positive charge; electrons have a negative charge while neutrons are not charged
It is these charged particles that give rise to electricity as we understand and apply it in todays electronic applications.
When two charged bodies are placed close together or connected, like charges will repel and unlike charges will attract each other.
If unlike charges are connected by a material that will allow the charges to move through it the charges will attempt to equal the number of protons (+) and electrons(-) in each body.
If a substance allows electrons to move through it easily it is known as a conductor.
If it does not allow the passage of electrons it is an insulator.
The flow of electrons along a conductor, to equal the charges, is an electric current.
p 7, 8
An electric current is the ordered flow of electrons along a conductor.
Because the electrons are the particles that can move the flow will be from negative to positive.
Electric current is represented in formula and circuit diagrams by the symbol ‘I’.
Current is measured in Amperes (A).
For a current to flow there must be a difference in charge between two points.
The difference in charge is known as a Voltage, Potential Difference or Electromotive Force.
Voltage uses the symbol ‘V’ or ‘E’ for formula.
Voltage is measured in Volts (V).
For a current to flow there must be a conductor connecting two points of different voltage.
Where ever we have movement we have an opposing force.
The opposition to current flow is Resistance.
Resistance uses the symbol ‘R’ for formula.
Resistance is measured in Ohms (Ω).
In a circuit the Voltage (forward pressure), Current (Electron Flow) and Resistance (opposition to flow) are related.
Ohms law states “The current in a circuit is directly proportional to the Voltage and inversely proportional to the resistance”.
As a formula - I = V/R
Or V = IR
Or R = V/I
NOTE: These formula are on the exam information paper.
Power is the ability of a force to do work.
In electrics, this can be turning a motor, causing a light bulb to glow or causing an electromagnetic wave to form around an antenna.
Electrical power uses the abbreviation ‘P’ for formula.
Electrical power is measured in Watts (W).
Electrical Power depends upon the Voltage and Current in the circuit.
As a formula: P = VI
Or V = P/I
Or I = P/V
NOTE: These formula are on the exam information sheet.
Direct Current (DC): Flows in one direction only.
A battery provides a source of DC.
Provided there is a circuit current will flow from negative to positive.
Many simple devices, such as light bulbs, will operate on DC regardless of which way the current is flowing.
The direction of current flow is known as the polarity of the circuit.
More complex electronic devices and/or circuits can be damaged if connected with incorrect polarity.
Excessive voltage can also damage electronic components.
Alternating Current (AC): The direction of current flow changes with time.
An alternator produces an AC current.
AC is easy to generate.
AC can be easily transformed to a different voltage.
AC is easier to produce and transform than DC.
The AC wave shape is a sine wave.
One complete wave is one cycle.
Alternators and oscillators create sine waves (AC).
Frequency is the number of complete cycles per second.
Frequency is measured in Hertz (Hz).
The frequency shown above is 4 Hertz. Mains is 50Hz.
An electric current is:
A. The voltage applied to a conductor.
B. The opposition offered to electrons in a circuit.
C. The ordered movement of electrons in a circuit.
D The heat generated by moving electrons.
ANSWER: C The ordered movement of electrons in a circuit.
Electrical Power in measured in:
ANSWER: A. Watts
If 10 Volts is applied to a circuit containing 5 Ohms resistance a current of _______ will result.
A. 0.2 Amps
B. 2 Amps
C. 0.5 Amps I = V/R
D. 5 Amps
ANSWER: 2 Amps
In air, the velocity (v) of radio waves, is 300, 000,000 metres per second.
The wave length is the distance the front of the wave has travelled in the time taken for the wave to complete a cycle.
Distance travelled at 300,000,000 metres/sec
Quantity Indicator Unit Symbol
NOTE: Voltage is sometimes referred to as Potential Difference or Electromotive Force (EMF), the symbol E may be used.
Often the units we have to use are very small or very large.
Frequency is usually in thousands or millions of Hertz but current is often in thousandths or millionths of an Amp.
To avoid writing f = 3562000Hz or A=0.00125A, scientific prefixes are used.
Some of these are used every day.
1 Kilometre is a 1000 metres.
1 millimetre is 0.001 metres.
Factor Prefix Symbol
Millionth micro µ or u
Thousandth milli m
Thousands kilo k
Millions Mega M
The prefix can be applied to any Unit.
2MV = 2 Mega volts (2,000,000V)
2mV = 2 milli volts (0.002V)
5000V = 5kV
Kilo is 1000. So 5000 divided by 1000 = 5
4.7kΩ = 4700Ω
Big unit to smaller unit - multiply
1500mA = 1.5 A
Little unit to bigger unit - divide
0.6MHz = kHz
Big to little - multiply
1A = mA
Big to little - multiply
50mV = V
Little to big - divide
5MΩ = Ω
Big to little - multiply
If wavelength is the distance travelled while one wave completes then the frequency must affect the wavelength.
f = 1 Hz
With a frequency of 1Hz the wavelength will be 300,000kms
With a frequency of 3Hz the wavelength will be 100,000kms
f = 3Hz
Thehigherthe frequency the shorter the wave length.
The lower the frequency the longer the wave length.
The conversion chart will be available in the exam.
NOTE: The frequency is in Megahertz
1000 Volts is often represented as
ANSWER: C 1kV (kilovolt)
Wavelength has the symbol ____ and is measured in______.
A. Ω and metres
B. µ and ohms
C. λ and metres
D. λ and Hertz
ANSWER: C. λ (lamda) and metres
AC stands for:
A. Ascending Current
B. Analysis Current
C. Analogue Current
D. Alternating Current
ANSWER: D Alternating Current
Electromagnetic frequencies range from 0Hz to millions of Exa hertz. (Exa = 1,000,000,000,000,000,000)
The area of interest to us is the audio and radio section of the spectrum.
The normal hearing range is about 100Hz to 15 kHz.
The range for audio communication is 300Hz to 3kHz.
Amateurs generally operate in the HF, VHF and UHF bands.
HF (High Frequency) - 3 to 30MHz
VHF (Very High Frequency) - 30 to 300MHz
UHF (Ultra High Frequency - 300MHz to 3GHz
NOTE: These frequency bands will be on the exam information sheets
When drawing circuits, symbols are used to represent components.
There are ten that need to be known.
In the practical section of your exam you will be shown at least five which must be correctly identified.
The five must include the earth and antenna symbols
Occasionally a fuse may be drawn as
A lamp may sometimes be shown as
These alternatives will not be shown in the exam.
A resistor may also be seen as
The switch above is a single pole single throw switch.
These two must be known and correctly identified
The loudspeaker may be seen as
None of the alternatives will be used in the exam.
A simple voice transmitter consists of:
Frequency Generation stage - Oscillator
Feed line and antenna
The audio (or data) is combined with the carrier (radio frequency) in the modulation stage of the transmitter.
This can be done by amplitude modulation (AM) or frequency modulation (FM).
AM (amplitude modulation) can be used as an emission mode or further divided into upper or lower sidebands.
Single Side Band (SSB) is a form of Amplitude Modulation (AM).
p 16, 17
If the modulating audio has too much amplitude the resulting modulated waveform will be distorted.
The audio amplitude is controlled by the ‘ Mic Gain’ or ‘AF Gain’ control on most transceivers.
This control adjusts the amount of amplification in the audio amplifier.
The distortion, as well as making the transmitted signal hard to understand can cause the transmitter to splatter across adjacent frequencies causing interference.
The final power amplifier stage of a transmitter must be connected to a correctly matched transmission line and antenna to avoid possible damage to the transmitter/feed line and interference to other radio communications services.
The matching can be done by ensuring that all parts of the circuit have the same resistance or by transforming the voltage current ratio to eliminate the mismatch.
An antenna matching unit (often called an antenna tuner) can be used to eliminate the mismatch.
The coax is an unbalanced line.
The dipole is a balanced antenna.
To feed a balanced antenna with an unbalanced line without a mismatch a balun must be used.
BALUN stands for BALanced to UNbalanced.
The basic blocks in a receiver are:
Tuning and RF Amplifier
Tuner / RF Amp
This is the diagram you will be asked to identify blocks from.
p 18, 19
Note: The tuning is the first stage in the receiver.
Terms applicable to receivers
Sensitivity is the ability of a receiver to reproduce weak signals.
Selectivity is the ability of a receiver to accept one signal while rejecting signals which are close by, in frequency, and possibly louder than the wanted signal.
Stability is the ability of a receiver to remain on frequency through a variety of operating temperatures both external and internal temperatures.
AF Gain: Controls the amplification in the AF amplifier in receive mode.
Mic Gain: Controls the AF gain in the microphone circuit in transmit mode.
RF Gain: Controls the amplification of the RF amp in receive mode.
Carrier or RF Power: Controls the RF amp in transmit and so the transmitter output power.
Mode: Control the emission mode (CW, AM, USB, LSB etc) of the transmitter and receiver.
Band: Switches between amateur bands.
VFO: Variable Frequency Oscillator – Main tuning Control for both transmitter and receiver.
RIT (Receiver Incremental Tuning or Clarifier). Tunes the receiver without affecting the transmitter. Usually within about 2kHz.
XIT (Transmitter incremental Tuning): Tunes the transmitter without affecting the receiver. Usually within about 2kHz.
Squelch: Sets the signal volume which will activate the receiver.
Not all transceivers will have all of the above controls.
The section of a transmitter that generates the RF carrier is:
A. Audio Amplifier
D. RF Amplifier
ANSWER: B Oscillator
If a transmitter is over modulated it is likely to:
A. Transmit a higher power.
C. Generate FM instead of AM
D. Generate interference
ANSWER D Generate Interference
The ability of a receiver to receive very weak signals is known as:
D. Super ability
ANSWER B Sensitivity
There are two basic types of feed line.
Coaxial Cable (Coax)
Consists of a centre conductor for the signal surrounded by a dielectric (insulator) and an outer screen at earth potential.
Twin Feeder (Ladder line or ribbon cable)
Consists of two parallel conductors which are at opposite and equal potential.
Coax cable is most widely used for RF signals because of its screening qualities.
To maintain these screening qualities all plugs and sockets must be the correct type for the cable and the outer braid must correctly connected to the plug/socket.
The screen should be earthed.
If not correctly connected the outer braid may radiate and cause interference.
There is a large variety of connectors exist.
Common RF connectors include BNC, PL259, N Type, etc.
Ensure both inner conductor and outer braid are correctly assembled.
Connectors in bad condition or incorrectly assembled are a major cause of bad SWR and power loss.
Screen must be continuos through all plugs and sockets.
p 23, 24
Antennas transform AC signals into propagating radio waves.
Gain is the apparent increase in power by directing it in one (or two) direction(s).
Antenna size is determined by wavelength.
An antenna radiates both a magnetic and an electrical field.
These two fields are at right angles to each other
The electrical field is in the same plane as the antenna.
It is the electrical field that determines the polarisation of the antenna.
A vertical antenna is vertically polarised.
An antenna that is positioned horizontally is horizontally polarised.
In the practical session of the exam you will be required to identify several types of antenna, either by diagram or actual examples.
You will not be required to estimate the frequency band the antenna is designed to operate on.
There are several antennas outside which we will look at in a moment.
The dipole consists of two equal halves.
Normally built as a half wave antenna.
Is a balanced antenna and therefore needs either a balun or a twin feed line.
The folded di-pole is a broadband antenna.
Normally fed with a 300 Ohm TV Ribbon.
If coax fed a balun must be used.
QUARTER WAVE VERTICAL
Normally built as a quarter wave length antenna to conserve space but will function if built to half or full wave length.
The vertical (whip) needs a ground plane to operate properly.
The ground plane can be the ground, radials or a solid base like a car roof.
Common for mobile use.
Identifiable by the coil at the bottom.
The radials serve the same purpose as the quarter wave.
Better impedance match and gain than a quarter wave.
Yagi’s are a directional antennas.
Only the driven element radiates – on its own it is a dipole.
The director gives focus to give gain and the reflector(s) gives front/back isolation.
More directors may be added to add focus (narrow the beam).
Effective Radiated Power (ERP) is the power radiated in the direction of the maximum radiation.
ERP is the product of the power supplied by the transmitter and the gain of the antenna.
The antenna must be matched, in length, to the frequency being used.
This creates a challenge for multi band HF working.
SWR – Standing Wave Ratio is a measure of the mismatch of the antenna system to the radio output impedance.
A high SWR results in power being reflected back down the feedline to the transmitter.
This is inefficient and potentially damaging.
SWR meters give a ratio of transmitter power (or forward power) to reflected power.
Some meters will also show the actual power levels, forward and reflected.
They are valuable for checking power, correct antenna design, installation and operation.
A sudden change in SWR will usually indicate a fault in the antenna system.
Dummy Loads are resistances used in place of antennas for tunning and testing without actually radiating a signal.
Radio waves nominally travel in straight lines and get weaker as they travel.
Diffraction, the slight bending around buildings, spreading out after passing through a narrow gap, following land contours etc, does occur.
Radio waves (especially at UHF & above) will also bounce off solid objects although some absorption, depending on the material, will be present.
Refraction is the bending of radio waves.
Other factors that affect propagation are meteor scatter, aurora’s and for microwave ranges rain and tropospheric scatter.
VHF/UHF normally has almost line of sight propagation.
A clear path is better to increase signal strength than an increase in power of 10 or 100 times.
For example a satellite can be reached with only a few watts if there are no obstructions whereas a signal travelling 5 -10 kms through trees and buildings will be almost unreadable. An increase antenna height will beat an increase in power.
Diffraction/refraction over the horizon will occur but is limited.
Buildings and hills cause shadows and path loss.
In towns the reflection and scatter caused by many buildings will improve expected reception.
Refraction at UHF/VHF can be caused by high/low pressure – often called ducting or lift.
These ducts can extend the range of U/VHF signal by hundreds of kilometres.
The main difference between VHF and HF propagation is the effect of the ionosphere.
The ionosphere is layers of ionised air 70 – 400kms above the earth.
They are created by the suns rays on the upper atmosphere and therefore vary from day to night and season to season.
They are also affected by sunspot activity.
It is the Ionosphere that makes long distance HF communications possible.
The ionised layers refract (bend) HF radio waves but have little or no effect on VHF and above.
The higher the frequency the less bending effect.
Signals that are returned may make a second hop.
The purpose of an antenna is to:
A. Let people know you are an amatuer
B. Allow balanced transmission lines to be used.
C. Convert electrical signals into radio waves.
D. Provide a place for birds to perch.
ANSWER: C Convert electrical signals into radio waves.
The longer the antenna:
A. The higher the frequency of operation.
B. The lower the frequency of operation.
C. The polarisation will be vertical.
D. The more power it can produce.
ANSWER: B The lower the frequency of operation.
As a radio wave is radiated away from the antenna it becomes:
C. Less polarised.
ANSWER: B Weaker
Electro Magnetic Compatibility (EMC) is the ability of an electronic device to operate properly, without interference, in the presence of electromagnetic radiation.
EMC has two aspects:
1. Avoidance of generating interference.
2. The immunity of your own equipment and appliances from being interfered with.
Factors which will effect the amount of interference generated include:
1. The more power emitted, the greater the likelihood of generating interference.
2. The mode of emission that is being used has a great effect on interference.
3. The closer the antenna to the other equipment the more likelihood of creating interference.
4. Good earthing of equipment will help prevent interference.
There are two types of earthing.
The normal mains earth, which is provided by the third pin (normally vertical) on the normal three pin plug.
This is designed to cause a fuse to blow if the equipments outside case becomes live due to a fault inside the equipment.
It is essential for safety reasons that mains earths are correctly connected.
Ensure that equipment is run from a common mains earth to prevent earth loops – use filtered mains boards and ferrite rings correctly.
Radio Frequency (RF) earths are separate to mains earths and the two should not be mixed.
Mains earths are NOT designed to conduct Radio Frequencies to ground.
Good reception, especially on HF, as well as EMC performance, depends on good RF earthing.
If RF enters the mains system it may be conducted through the system and enter other equipment/appliances.
This provides a path to ground for RF currents which otherwise may enter the mains system and cause interference.
A good RF earth should consist of a copper stake well buried into the earth, as close as possible to the equipment, with a thick copper braid connection.
RF earths should be a separate earth stake, DO NOT try to use existing water or gas pipes as an earth.
AM/SSB can be easily rectified/detected, so is most likely to cause interference to domestic equipment.
Antenna siting and type of system can assist in minimising interference.
A balanced antenna system is less likely to create problems than an unbalanced system.
Maximise distance between transmitting and receiving antennas/equipment.
When using directional antennas avoid pointing them at neighbouring equipment/antennas.
Filters can be fitted to transmitting systems to stop unwanted radiation and to receiving systems to stop unwanted signals entering the system.
Filters can also be used on power supplies to stop RF entering the mains or interference from mains entering equipment.
Where used filters should be fitted as close as possible to the effected equipment.
A coil, preferably wound on a ferrite rod, makes an effective RF choke or filter.
Speaker wire wound as shown will prevent RF signals being fed through speakers.
If put into an antenna cable it will prevent weaker signals from interfering with TV or Radio.
Digital TV is effected quite differently.
The picture may become blocked (form squares like a jigsaw), jerky, freeze or disappear completely.
These symptoms are the same as a weak signal and the owner may suspect a TV problem rather than interference.
Repeaters are used to extend the normal VHF/UHF range.
The repeater has a transmitter of a different frequency to the receiver.
Each station receives and transmits on different frequencies.
Repeaters must have a time out mechanism.
When using a repeater always allow time for the repeater to reset.
Beacons are fixed transmitters on certainly frequencies which are used on HF to give an indication of propagation.
They may be timed to allow of network of world wide stations to transmit on the same frequency.
These systems allow repeaters that are equipped with the system (nodes) to link together throughout the world via the internet.
IRLP requires a radio to access the input repeater and receive the output where as Echo Link can be run from a registered computer.
Dual Tone Multi Frequency uses the same tones as mobile phones.
They are used to control repeater functions such as switching from high to low power, and for causing an IRLP or Echo Link repeater to link to another node.
Each IRLP or Echo Link node is designated a four figure number. When the number of a remote node is entered the local computer links to the called node.
Continuous Tone Coded Squelch System is a system where a sub audible tone is used to break the squelch on a remote receiver.
Interference often can cause a repeater to turn on and lock on while the interference is present.
By using CTCSS the receiver has to hear the tone before it will open the squelch and allow the receiver to activate.
In Perth all 70cm repeaters are CTCSS equipped.
Interference resulting in EMC problems can be minimised by:
A. Only operating from a mobile station.
B. Using vertically polarised antennas.
C. Careful siting of antennas.
D. Using dipole antennas.
ANSWER: C Careful siting of antennas.
One way that interference can be passed between equipment is:
A. By the mains power supply lines.
B. Moist atmosphere.
C. Gas Pipes.
D. RF chokes.
ANSWER: A By the mains power supply lines
DTMF stands for
A. Dual Tone Multi Frequency.
B. Double Tone Multi Frequency.
C. Dual Tone Modulated Frequency.
D. Double Tone Masking Frequency.
ANSWER: A Dual tone Multi Frequency
High voltage is extremely dangerous – Electrocution is possible with almost any voltage but remember high voltages can and will jump for an earth.
High currents as well as shocking, create heat and may melt insulation and cause fires.
RF radiation is dangerous as it will heat metal (rings, watches etc).
In addition to heating metal it will heat the human body and cause internal damage and external burns.
All items in a radio shack should be earthed and protected by RCD’s (Safety Switch’s).
Only items marked as double Insulated may be used with out a mains earth.
Have a clearly marked, easily accessible mains switch for the shack.
Fuses protect equipment from fire not people.
Avoid trip hazards caused by cords etc.
Working at heights, either on a ladder or up a tower, is dangerous not just from the falling aspect but also for people below from falling items.
Lightning is extremely high voltage and currents. Disconnect antennas during thunderstorms.
It is illegal to use power/telephone poles to support or anchor antennas, towers etc.
When setting up antennas be aware of power/telephone lines.
When operating mobile stations be aware of your antenna height.
Symptoms include loss of consciousness, breathing difficulty, weak ,erratic or no pulse and burns at entry and exit points.
NEVERapproach a victim of electric shock until you are certain the power has been disconnected.
Be especially careful if any liquid is present.
The first action must always be to ensure power is off.
Check for response, breathing and pulse.
Start resuscitating the victim.
Get someone else to call 000 and get assistance.
If patient is conscious reassure them, cool burns. Never use oils or ointments on burns.
If a fall has occurred do not move the victim in case of spinal injuries.
With thanks to
Chelmsford Amateur Radio Society
Westlakes Amateur Radio ClubInc
Fred Swainston VK3DAC
The Wireless Institute of Australia