# UK Amateur Radio ## Foundation Licence 2002
## EMC Part B
### A more detailed look ### Use a good earth? SEEK EXPERT ADVICE for your station This is a tricky area as there have been developments in the safety angle in the home regarding electrical installations. In the past it has been considered part of good radio shack practice to have a good RF earth connection in an HF amateur radio station. However this may defeat the objectives of the supply companies PME earth system. #### So as a practical point with regard to setting up your station seek advice from an electrical specialist who is NICEIC registered explaining to the contractor what you propose to do. Your safety is at stake here and this course is designed with safety in mind. So far at the written assessment goes if you see a question that is about earthing stake make an educated guess at the answer bearing in mind the old thought was that an earth stake will them minimise RF current entering the mains earth system and the potential to cause interference to other electronic equipment.
### Filtering techniques Seek expert advice for your station There are many methods and devices available for reducing the level of unwanted signals leaving a transmitting installation. Low Pass filters may be fitted to transmitter antennas and there are special filters for mains leads. All devices should only be fitted as recommended by the supplier. The immunity of most types of equipment can be increased by fitting suitable external chokes and filters in the mains lead and or TV antenna lead.These are used by passing a few turns of the leads or cables through ferrite rings. These devices work by increasing the impedance (A.C. resistance) of the lead to reduce the flow of unwanted signals at higher frequencies. Do not attempt to fit any device of which you are uncertain. The danger of fire or electrocution is only too real.
### Using filters The filters should be fitted as close as possible to the affected device that is as close as possible to the aerial connector on a TV and where the mains lead enter the TV. Then the smallest piece of cable is left exposed to RF pickup.
A ferrite ring is used as a choke. The cable that is wound on the ferrite ring could be the mains lead, an aerial lead, or loud speaker leads. The only type of filter that can be used be used safely on a mains leads is the ferrite ring. This is because the ring does not change in any way the structure of the cable when wound onto the ring. Home made filters other than ferrite rings are potentially dangerous and must only be used if commercially made to high safety standards.
### TVI |
The pictures above show TVI - TeleVision Interference. These pictures are of actual interference and are not simulated. They occurred by using a hand held transmitter within a few feet of the TV. Consider how you would feel if your TV picture was blanked out when you are watching your favourite program. | Such interference is quite likely to result in neighbour disputes. You must understand that not everyone likes the hobby of amateur radio and it is your duty to be careful and avoid the likelihood of causing interference that could lead to big arguments.
### So remember Should you ever experience a neighbour who mentions that they have a problem, whilst not admitting to being the cause show sympathy and agree to try to sort it out by carrying out test with them to check where the EMC problem might lie. If this cannot be done amicably then the local office of the Radiocommunication Agency will need to be involved to help resolve the problem. ### Shut down This will almost certainly mean the immediate shutting down of your station for a period of time to let matters cool down. Then when the air is better there will be a better chance to sort things out. ### Keep your own TV clear of EMC problems The best way of showing you care is to show that your own TV - Radio - etc does not get any problems. However if you do have problems on your own equipment then solve them immediately - so that if a neighbour calls you can shown him that you don't cause interference to your equipment and therefore the realization may dawn on the neighbour that it is he who has a little bit of sorting out to do.

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