Q: If my CD unit is playing when my telephone rings, it makes an odd noise and goes completely silent, remaining so until a few seconds after I have picked up the phone.
Very occasionally this silence begins before the first ring is heard. Why is this? The CD player is an extremely simple and unsophisticated unit without any form of remote control. It outputs into the auxiliary input of nearby equipment which itself has remote switching of all its components, namely radio receiver, amplifier, tape decks and record player, using a single remote control handset.
The telephone is in the same room with a built-in answering message tape unit which is not normally switched on when I am present. It is about five metres from the CD.
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On the same telephone system are two other phones, one of which is on the floor above and about seven metres from the CD. This is of the type with its own short-range transmitter to transmit to a portable handset. When the phenomenon occurs, the handset is normally sitting on its base unit in the charging mode.
A: This is caused by the CD player picking up the radio-frequency radiation from the cordless telephone base station. This is causing the player鈥檚 automatic muting to operate, as if the data from the disc were corrupted.
According to the applicable electromagnetic compatibility standard EN55020, the CD player should be immune to RF field strengths up to 2 volts per metres. If the cordless telephone is an approved type (with a green label), it should not be producing such a high field strength at 7 metres, so the immunity of the player is suspect.
It is easy to test this explanation by disconnecting the cordless base-station to see if the effect disappears.
A: This situation is common. Other examples include cellular telephones interfering with their users鈥� car electronic ignition systems which can cause the car to stop dead, or a passing police radio causing a burglar alarm to go off which then brings the officers back to investigate a few minutes later 鈥�