7a.1 Recall that electromagnetic compatibility (EMC) is the avoidance of interference between various pieces of electronic equipment.
The
letters EMC stand for Electromagnetic Compatibility. This is all about
stopping one piece of electronic equipment interfering with another
piece of electronic equipment.
7a.2 Recall that radio transmitters can cause interference to nearby electronic and radio equipment.
Because they are designed to transmit
radio waves a radio transmitter can be a source of interference to
nearby electronic equipment.
7a.3 Recall that radio receivers can also suffer from interference from local sources. Radio
receivers used by amateurs are very sensitive and are subject to
picking up interference from local sources such as TV sets.
7a.4 Recall that interference occurs through local radio transmissions being conveyed to the affected equipment through pick up in house wiring, TV antenna down-leads, telephone wiring etc., and (particularly at VHF/UHF) by direct pick-up in the internal circuits of the affected equipment.
Radio waves from an amateur transmitter can be picked up by local
pieces of electronic equipment. The main ways in which RF signals enter
other equipment are:
By pick up from the
mains electricity supply. The mains wiring acts like an antenna and
carries the RF to the equipment where it causes interference.
The coax from a TV or
satellite TV dish can also act as an antenna, picking up radio wave and
causing interference to the picture and sound.
Radio waves (particularly VHF and UHF) can be picked up directly by the circuit boards in the equipment.
EMC - Station design for EMC
7b.1 Recall that EMC problems can be minimised by siting antennas as
far away from houses as possible, as high as possible, and using
balanced antennas at HF.
Recall that, at HF, (horizontal) dipoles are less likely to be a
problem and that end-fed wires present significant EMC problems.
Recall that information on the avoidance of interference by the correct
choice and siting of antennas and suitable operating procedures is
readily available from several sources.
Here are some ways to reduce EMC problems:
Keep the antenna as far away from houses as possible.
Put the antenna as high up as possible
Use balanced antennas such as dipoles rather than end-fed wires which are more likely to produce interference
Use horizontal dipoles rather than vertical antennas which are more likely to produce interference.
For further information on reducing EMC problems there are several sources See RSGB and ARRL websites
Reduce your power to the minimum required for communication
7b.2 Recall that the more power a station runs, the more likely it is to cause interference.
Recall that some types of transmission are more likely to cause interference to TV, radio and telephones than others.
Recall that SSB is the one of the poorest in this respect. FM, CW
(Morse) and some of the HF data modes (such as PSK31) are much
better.
The more power is used the greater the risk of creating interference, so keep the power down if you are causing problems. Some types of transmission are more
likely to cause EMC problems. SSB is probably the worst. Modes that
cause less interference include FM, CW (Morse) and some HF data modes
such as psk31.
