chelmsford amateur radio society emc (7) e lectro m agnetic c ompatibility
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Chelmsford Amateur Radio Society EMC (7) E lectro M agnetic C ompatibility. EMC Regulations. All electronic equipment is capable of radiating and absorbing radio frequency (RF) energy. - PowerPoint PPT PresentationTRANSCRIPT
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Chelmsford Amateur Radio Chelmsford Amateur Radio Society Society
EMC (7)EMC (7) EElectroMMagnetic CCompatibility
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
EMC Regulations
• All electronic equipment is capable of radiating and absorbing radio frequency (RF) energy.
• The The principle behind ElectroMagnetic Compatibility is that equipments should limit radiation to below a specified level and also be able to withstand a certain level of incident RF radiation.
• The levels are given in the EMC regulations.
• You need to be aware that they exist, but you will not need to know them for the exam.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Domestic Environments
• Transmitters in domestic environments may give rise toRF fields stronger than the specified limits.
• Special measures may have to be taken to limit interference.
• Intermediate Licence allows 50 Watts - and this is likely to cause interference in a domestic environment.
• You may have to reduce power if you can not cure the interference.
• This may be enforced by the Secretary of State / Ofcom
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
New Equipment
• New equipment, manufactured since 1996, should meet the EMC directive immunity requirements and the incidence of problems with new equipment is usually lower.
• Older equipment and poor installation practices in new equipment do exist and problems do occur.
• A TV downlead does have a service life:
– It is subject to water ingress.
– PVC Breakdown due to UV
– Poor quality leads have very little copper braiding with poor screening properties
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Station Layout• Correct interconnection of the
transmitter, microphone, power supply, SWR meter and band or low pass filters, using appropriate cables, minimises EMC problems.
• Always have a good layout to keep RF and audio or power leads apart.
• Use:
– Good quality screened cable with correctly fitted plugs and sockets
– Filters (on the antenna side of the SWR meter)
– Correct earthing.
Station LayoutStation Layout
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Filters• Filters can be fitted in the leads from the power supply to the
transmitter to help minimise RF energy entering the mains wiring.
• Ferrite ring filters on the 12V power leads and the mains lead.
– Home made power supplies should fit filters by design.
• Any other equipment in the shack, especially if interconnected to the transmitter, such as:
– TNCs, Voice keyer, CW keyer, Other audio Interfaces
– Computer sound cards, TV cards, Digital camera leads.
• Should be similarly filtered on:
– signal leads, power leads, mains leads.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
RF Earth - What is one
• A good RF earth will comprise an earth rod driven into the ground plus a number of radials so as to form an earthed mat under the antenna.
• The ends of the radials may also have earth rods.
• The radials will be just under the grass, out of sight and away from damage but still serving the purpose.
• It must be close to the transmitter and ideally at the point where the feeder enters the building.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
RF Earth - What is one
• A Heavy Duty Earth Wire (thick copper braiding) should run directly to the back of the transmitter.
• If the feeder terminates in a socket on the wall with a fly lead to the transmitter, an extra earth lead should be connected from the termination of the RF earth lead at the wall socket, to the transmitter.
• Do not just rely on the braid of the fly lead.
• Mains Safety earths and RF earths are two separate requirements..
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Spurious & Harmonic Emissions
• A general coverage receiver is the most effective tool available in the average shack.
• Scan methodically through the bands, stopping on odd signals and switching off the suspect item whilst listening to the signal on the receiver.
• Calculation of harmonics are covered in transmitters.
• The wavemeter is deaf in this regard, but can work.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Siting Antennas
• Siting a transmitting antenna close to mains wiring, TV or radio aerials, and downleads, is a potential problem
• Especially the use of a loft or indoor transmitting antenna.
• The field close to the transmitting antenna is very strong.
• Far higher than any equipment can reasonably be expected to withstand
• Signals induced in any wiring, mains, TV, audio, telephone or alarm system, will be considerable and must considered.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Indoor or Loft Transmitting Antennas
• Indoor or loft transmitting antennas have two disadvantages:
– Closeness of coupling and any TV antenna sharing the loft.
– Attenuation of the wanted signal as it passes through the roofing materials.
• Being an indoor or loft transmitting antennas make it more susceptible to causing / receiving interference.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Forms of Interference caused by Amateur
Radio• The forms of interference caused by amateur radio
transmissions.
– Patterning on the TV screen,
– Loss of colour, voice on TV sound,
– Sounds on / loss of sound on Radio,
– Sounds on Telephone,
– Sounds on audio systems.
• Interference to digital televisions is different.
– The picture may freeze, become jerky or disappear.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Good Analogue Picture
• A good example of an analogue TV picture.
• Received with no interference.
BBC2 Sports Program
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
FM Transmission
• Wavy, herringbone patterning on TV
• Possible loss of colour
• No effect on sound
• But on severe cases may cause distorted or loss of sound. Herringbone patterning on TV
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
AM or SSB
• Similar patterning on screen,
• Possibly in time with speech,
• Distorted voice like sounds, can be intelligible.
AM / SSB Patterning on screen
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
CW - Morse code
• Possibility of flickering picture or wavy effects,
• Possibility of clicks or distortion on sound.
Morse code - possibility of clicks or distortion on sound
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Digital TV
• Digital TV is affected quite differently.
• There is no visual evidence of what is happening other than the picture becoming jerky, forming blocks as if it is a jig-saw,
• Freezing or disappearing.
• These effects are the same as if there is a weak signal.
• The neighbour is more likely to call the service engineer believing a fault on the TV.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Other Sources
• Other sources and effects on a TV are:
– Electric Motors Spots on TV screen
– Possibility of buzz (burr) on sound
– Thermostats 2-10 seconds of spots and lines on screen
– Possibly quite intense and noise like screwing up paper on sound
– Vehicle ignition spots/lines on screen,
– Clicks on sound in time with engine speed.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Direct (internal) pickup
• Direct pickup in affected devices tends to be independent of the transmitted frequency.
• Direct (internal) pickup and conducted pickup e.g. by:
– loudspeaker leads
– Internal wiring
– PCB’s
– etc
• And occurs over a wide range of frequencies.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Masthead and Downlead
• Masthead and Downlead TV amplifiers are broadband and so they amplify a wide range of frequencies, including amateur frequencies.
• This can overload the TV input.
• If the masthead amplifier is needed, a filter at the TV input will help as will a band specific amplifier.
• Avoid using Masthead and Downlead amplifiers in conjunction with a video unit.
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Ferrite Rings
• Ferrite rings are effective for R.F. signals on mains and audio leads and for R.F. signals picked up by the screen of coaxial feeders and downleads.
• If the signal is picked up by an antenna on the inner conductor, then ferrite rings are ineffective, a filter tuned to the appropriate frequency is needed.
• In-line mains suppression filters are effective for interference conducted along the mains wires.
• Transmitting into a dummy load is a good test for any unwanted R.F. being conducted out of the transmitter along its power supply leads and into the mains
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Conducting Tests & Neighbours
• Conduct tests in co-operation with the complainant in instances of interference.
• Remember that a logbook can be of considerable assistance in confirming sources of interference to neighbours.
• The Complainant should also keep a log of the instances of interference.
• Ofcom can require Logbooks to be kept over a period of time to assist Interference Investigations
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Chelmsford Amateur Radio SocietyIntermediate Licence Course
Christopher Chapman G0IPU Slide Set 11: v1.2 16-Jun-2007 (7) EMC
Help from Ofcom & RSGB
• Advice is available from the RSGB EMC Committee http://www.rsgb.org/emc/
• Local Ofcom officers will help with cases of interference.
• RSGB have a wide range of EMC information leaflets on their EMC website. The RA Archive on the Ofcom Website also has:
RA-234: EMC and the Radio Amateur
RA-179: Television and Radio Interference
RA-272: Problems Thermostats can cause to Television & Radio Reception
RA-323: Guidelines for Improving Television and Radio Reception
RA-415: Guidelines for Improving Digital Television and Radio Reception