1. AMATEUR RADIO TRAINING
Electromagnetic Compatibility
Release: v1.21
hamtrain.co.uk

2. Electromagnetic Compatibility
What causes interference?
Ways to reduce interference
Transmission modes
Antennas & earths
Good station design

3. 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

4. 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

5. Causes of Interference
Aerial and/or aerial cabling pick-up
Speaker cable pick-up
Equipment with poor immunity / unshielded equipment
Via mains earth

6. 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

7. Video: Digital TV Interference

8. Digital TV Pixelation

9. 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

10. Filters Clip-on ferrite High-pass or band-pass TV filter
Wound ferrite ring
Ferrite filter on a power lead
Safety note: Home-made filters are potentially dangerous

11. Modes and EMC FM – Causes less interference “friendly modulation”
AM / SSB – Causes more interference, as the amplitude varies with the signal
Morse / CW – “Key clicks” can be a problem if on-to-off is not smooth
Data – Normally constant modulation, so less of a problem than speech
Frequency Modulation
Amplitude Modulation
Data

12. 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

13. Antennas and EMC 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

14. Station Design Use good quality cables and connectors
Have a good RF earth
Use mains and RF filters
Balanced antenna
Balun
Coax
PSU
Transmitter
Filter
ATU
VSWR
Filtered Mains
RF Earth

15. Balanced Antenna Setup
HF antenna sited away from house & TV antenna
Good quality co-ax
RF earth close to shack
Balanced Antenna
Balun

16. End-fed Antenna Setup Unbalanced system
Feed from the end of the garden
RF earth close to shack

17. Example of Poor EMC Setup
Fed from upstairs shack
No RF earth
Proximity to TV antenna

18. 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

19. 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

20. Electromagnetic Compatibility
Any questions?
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