Transcript Foundation: EMC

AMATEUR RADIO TRAINING
Electromagnetic Compatibility
v1.13 © essexham.co.uk
ELECTROMAGNETIC COMPATIBILITY
• What causes interference?
• Ways to reduce interference
• Transmission modes
• Antennas & earths
• Good station design
What is EMC?
• Electromagnetic Compatibility (EMC) is the
avoidance of interference between two pieces of
electronic equipment
• Transmitters can cause interference to other
equipment, such as a neighbour’s TV and radio
• You need to understand the impact, and how to
minimise the likelihood of causing unwanted
interference
Interference
• There is a chance that your signals can
cause interference to:
• TV sets / computer monitors
• FM, AM & DAB Radio
• Hi-fi units
• Cordless and fixed-line phones
• Touch lamps
• Baby monitors
• Security alarms / CCTV
Causes of Interference
• Aerial and/or aerial
cabling pick-up
• Speaker cable pick-up
• Equipment with poor
immunity / unshielded
equipment
• Via Mains earth
Digital TV Interference
• RF interference to digital TV will pixelate the picture and
cause breakup to sound
• Worse if weak Freeview signal, or using a TV signal
booster
Analogue TV Interference
Analogue service discontinued
in 2012
Interference included:
• Wavy lines
• Image roll
• Bars
• “Herringbone pattern”
TV Interference – Video Example
(Press above to start short video example)
Minimising Interference
Depending on the problem:
• Reduce field strength by moving the transmitting
antenna further away
• Reduce the power
• Fit filters to the ‘pickup’ cabling
• Using filters on mains power supply leads
• Addressing earth problems
Filters
Clip-on ferrite
Wound ferrite ring
High-pass or band-pass TV filter
In-line ferrite mains filter
Modes and EMC
• FM – Causes less interference
“friendly modulation”
• AM / SSB – Causes more
Frequency Modulation
interference, as the amplitude
varies with the signal
• Morse / CW – “Key clicks” can be
a problem if on-to-off is not smooth
Amplitude Modulation
• Data – Normally constant
modulation, so less of a problem
than speech
Data
RF Earth
Use an RF earth to minimise RF leaking into mains
• Do not use Mains earth for RF!
• Do not use radiators / water pipes
• Use a copper stake in the ground close to shack
• Use heavy-gauge wire to connect from transmitter or ATU
Antennas and EMC
Dipole
• Dipole is commonly used for HF
• This is a ‘balanced’ antenna
• Connected to transmitter / ATU
using unbalanced coax cable
• Uses a ‘balun’ (balanced-to-
unbalanced)
• The shield of the coax is
connected to the RF earth
Station Design
• Use good quality cables and connectors
• Have a good RF earth
Balanced antenna
• Use mains and RF filters
Balun
Coax
PSU
Transmitter
Filtered Mains
Filter
VSWR
ATU
RF Earth
Balanced Antenna Setup
• HF antenna sited away from house & TV antenna
• Good quality co-ax
• RF earth close to shack
Balanced Antenna
Balun
End-fed Antenna Setup
• Unbalanced system
• Feed from the end of the garden
• RF earth close to shack
Example of Poor EMC Setup
• Fed from upstairs shack
• No RF earth
• Proximity to TV antenna
EMC and Neighbours
• It pays to be helpful and co-operative
• Most problems can be resolved easily and cheaply
• Get free advice from the RSGB EMC Committee
• Your neighbour may consult Ofcom (for a fee).
• Ofcom may ask you and the neighbour to keep a log to
confirm interference is related to your transmissions
EMC Summary
• EMC – Electromagnetic Compatibility
• Understand the symptoms & causes
• Have a good RF Earth
• Use the right type of antenna and good quality cable
• Understand how to position an antenna to minimise
interference
• Correct station and shack set-up
• FM is more “friendly” than other modes such as AM / SSB
• Understand the type (and correct use) of filters
• Resolving problems – Keep a log, and consult RSGB EMC
Committee
ELECTROMAGNETIC COMPATIBILITY
Any questions?
essexham.co.uk/train