EMC - Immunity of radio receiving and other devices and filtering techniques.
7c.1 Recall that the ability of any piece of electronic or radio equipment to function correctly in the presence of strong RF signals is known as "immunity". Recall that the immunity of most types of equipment can be increased by fitting suitable external chokes and filters in mains or TV antenna leads. Recall that the filters should be fitted as close to the affected device as possible.
In order for a piece of equipment to work well in the presence of strong RF signal it has to have a high level of immunity. Here are some tips for increasing the immunity of a piece of equipment:
Fit
RF chokes and filters to the mains lead. This will reduce the strength
of RF signals entering via the mains wiring. In its simplest form the
mains cable can be wrapped round a ferrite ring
or rod. Mains filters can be purchased that consist of an in and out
connector. Inside the filter are inductors and capacitors designed to
filter out RF signals from the mains lead before it enters the mains
equipment. The filter shown opposite is designed to be fitted inside a
piece of equipment.
Fit a high pass filter in the coax before it enters the TV.
This will allow the high frequency TV signals to enter the TV, but
reduce the strength of HF signals from a nearby transmitter.
7c.2 Recall that anything fitted to the mains wiring must be properly made for the purpose. Understand that home-made filters (other than ferrite rings) are potentially dangerous. Recall
that information about the purchasing, making and fitting of chokes and
filters is readily available from several sources. 7c.3
Recall that the function of the RF earth connection in an HF amateur
station is to provide a path to ground to minimise RF currents entering
the mains earth system and causing interference to other electronic equipment.
Wrapping the mains cable entering a piece of equipment round a ferrite ring is not
particularly dangerous, but any filter that involves soldering to mains
cable needs to be made properly otherwise it could be a health risk.
Until you have a lot of experience it is best to purchase ready-made
mains filters which only involve plugging the mains in and connecting
the mains to the equipment.
There are many sources of information about making, building and
fitting chokes. For example see the RSGB web site for the purchase of
filters:
EMC - Social issues of Interference
7d.1 Recall that EMC problems have the potential for causing neighbour disputes. Understand the need for diplomacy, the sources of advice available and the role of the local office of Ofcom.
If you live close to other housing
there is a high chance that one day someone will knock on your door
complaining of interference, demanding that you stop using your
equipment so that they can continue to watch their TV. Try
to be diplomatic. Discuss the type of interference and when it occurs.
If this coincides with when you use your transmitter then try reducing
power or changing frequency. Make it clear that most types of
interference can be cured fairly simply either at the transmitter end
or at the neighbours end. Explain that filters are available to
reduce, for example, TV interference and that wrapping cables round a
ferrite ring can also help. If they just want you to stop using your
equipment you could refer them to Ofcom.
