6B1 Recall that speech transmissions, particularly AM and SSB may cause speech like sounds in analogue radio, audio systems and telephones. Recall that FM transmission is more likely to mute or reduce the volume of the wanted signals (audio or RF).
Domestic equipment like household telephones, Audio and Hi-Fi systems, and analogue radio (LW,MW,and SW) can be interfered by your amateur radio signals. SSB and A.M. signals for instance, can be picked up in the speaker or telephone leads and block received audio and actually come out as sound (of your speech). An FM transmission can swamp domestic audio up to the point where the householder suffers reduced or no audio.
6B2 Recall non-radio sources of
interference and their effects:
⦁ Arcing thermostats
⦁ Vehicle ignition systems
⦁ Electric Motors
⦁ Computers and peripherals
⦁ Switch mode power supplies
⦁ Plasma TVs
⦁ Very high bit rate Digital Subscriber Line (VDSL)
equipment
⦁ LED lighting
⦁ Solar photovoltaic (PV) inverters
Domestic equipment like household telephones, Audio and Hi-Fi systems, and analogue radio (LW,MW,and SW) can suffer from external noises from these stated sources.
Recall that this gives rise to various buzzing sounds on analogue radio receivers which can correlate with the nature and use of the interference source e.g. bursts of undesirable sounds when a thermostat opens or closes.
Central heating thermostats can give clicking or buzzing sounds in domestic radios and telephones. Vehicles can give clicking or vibrating sounds. The others in the list give wideband noise. All these can prevent enjoyment of a radio or TV program to a listener.
Transmitters are not the only sources of interference to TV's and their effects are different.
The key sources and effects are :-
Electric motors
On vision (TV picture) -- Spots on the TV screen
On Sound -- the possibly of a buzzing or some other continuous noise
Thermostats
On vision -- a regular appearance every 5 to say 10 minutes of a burst of spots and lines on TV screen which are quite intense which last say 2 to 10 seconds
On sound -- the screen interference is accompanied by short period of a noise like screwing up paper or a sort of rasping buzzing sound.
Some how students
seem to miss this part where thermostats are mentioned maybe
is it because they do not understand that a thermostat is used in
the residential environment to regulate the
temperature of the room whether it is
by switching on and off an electric heater
or the central heating pump. Thus there will be semi
regular operation of the thermostat as the room cools
down to turn the heating on and when it
reaches the selected temperature switches the heating off. The
operation of the switch causes the
electrical interference in the TV as indicated above.
Vehicle ignition
On vision -- spots / lines on the TV screen
On sound -- with clicks which rise and fall with engine speed.
NOTE:-
Analogue TV transmissions in the UK have ceased although there may be some analogue TV's with external "Set top boxes" still in use for a while. These remaining analogue sets may continue to show some signs of local interference from radio transmissions, electric motors and car ignition systems. Common effects include wavy lines, loss of colour, dotted lines, loss of sound and audio breakthrough.
6B3 Recall that interference to Digital Audio Broadcasting (DAB) may cause loss of signal (muted audio) and to digital televisions may cause the picture to freeze, appear to pixelate; that is break up into larger squares, become jerky or disappear.
Due to direct pick-up of your amateur radio transmissions, it can cause blocking by the effect of swamping the signals that the radio or TV are tuned to, proving that digital signals are not immune. A DAB radio can be blocked at the aerial causing the station that is listened to be muted. Similarly in a TV the station watched can be blocked and/or weakened. This can cause muting of the audio, but the picture can be reduced to visible effects by pixelation of the images being watched.
There are several distinctive effects of RF EMC problems on Analogue Equipment whether it is amateur or other radio transmissions - these are :-
herring-bone patterning on the TV screen usually caused by an FM transmission,
loss of colour,
voice on TV sound, radio, telephone or audio systems usually caused by an SSB transmission
When it comes to Digital televisions the situation is different. RF interference may cause :-
the picture to freeze,
the picture to become jerky,
the picture to disappear.
The origin of some of the text on this page is from the RSGB with additions by the web master