6E1 Recall how to interconnect the transmitter, microphone, power supply, SWR meter and band or low pass filters, using appropriate cables, to minimise EMC problems.
With all of EMC you have to consider where the RF is entering the system.
So far as this section of the syllabus is concerned RF can enter through:-
the Microphone lead so a clip on filter may be needed adjacent to the transceiver
via the power lead whether that is the Mains or the DC supply so clip on filter may be needed adjacent to the transceiver
HF station
On the route between the antenna and the transceiver the order of connection is as follows:-
Transceiver - SWR meter - ATU - Band / low pass filters - then the antenna
VHF / UHF station
in a VHF / UHF station the LPF is substituted for a band pass filter as you are either on 145 to 146MHz or 430 to 440MHz, single bands thus an ATU is rarely used.
Ensure that the coaxial feeder and connectors used are all of the best quality that you can afford. Coaxial feeder is used due to its screen properties of the outer braiding keeping the signal contained within the cable are much as possible.
Also you need to keep RF and audio and power leads apart from each other else you are making it easy for the RF signal to enter the other lead especially if they are not screened.
6E2 Recall what constitutes a good RF earth, its purpose and use.
If you get a question in the exam referring to a good earth for a transmitter then the question is relating to the RF earth and not the Mains power earth
A good RF earth will comprise an earth rod driven into the ground plus a number of radials so as to form an "EARTH MAT" under the antenna. The ends of the radials could also be attached to earth rods.
The radials can be for safety just placed under the surface of the grass and allow the new grass to grow over or through and obscure. Do consider the safety of anyone walking over the lawned area and tripping up.
The RF earth should be connected to all of the equipment in the shack to ensure as far as possible the effectiveness of the various screening, cables chassis of equipment excludes unwanted RF energy.
E3 Understand that siting a transmitting antenna close to mains wiring, TV or radio antennas and down-leads is a potential problem exacerbated by the use of a loft or indoor transmitting antenna
So what can pickup your RF with regards to proximity to your antenna:-
mains wiring
TV and radio aerials and down leads
Whilst not mentioned in the syllabus at this point we can also include internet cabling, alarm and CCTV cables.
Thus if you have decided for what ever reason that you have to locate your antennas in the roof space (loft) or any other indoor antenna, you are in fact exacerbating (making worse) the EMC problem.
The field strength from your antenna reduces with distance and therefore you always want to have as much distance between your antenna(s) and ALL wiring.
6F2 Recall that when routing RF cables and mobile radio DC power leads within vehicles they should not be routed in parallel with the vehicle wiring loom and they should not be run near electronic control units.
So the general rule is keep your RF equipment away from other equipment cables for 2 reasons. One is that you do not pick up noise on receive, and second you do not interfere with other equipment.
This is also true if you have a mobile installation in your vehicle. It is important to keep the radio D.C. supply cabling to your transceiver away from the vehicle's wiring loom so that you do not pick up ignition noises on receive that can prevent you hearing stations which would blank out any station you wish to receive. Note that your transmit aerial and co-ax cable to it are also kept away from the vehicles cables so you RF does not interfere with the vehicle's workings.
Recall that radio frequency energy can cause interference to vehicle electronic circuits, including audio systems, navigation systems, remote locking, alarms and engine fuel management systems particularly when operating equipment with an RF output of 10W or more.
One thing you must not do when out mobile is to transmit while inside a petrol filling station. The RF energy could ignite any petrol fumes.
All electronics parts of your vehicle can be affected by you transmit signal. Most vehicle electrical devices are able to absorb a tiny amount of RF so best to keep your transmit power down, say under 10W. Above this level you may interfere with sat-navs, car computer, remote locking and braking systems, Fuel control systems and generally make the car unsafe to drive. We do not want that scenario.
6F3 Understand that mobile antenna location can affect the radiation field strength within the vehicle; e.g. wing or boot mounted antennas are likely to produce higher exposures than roof mounted antennas.
Also while setting up a mobile installation it is preferable to have the antenna on the roof so that the metal of the roof acts as a ground plane, but mostly for your own safety as it isolates you and the car from most of the RF field. Positioning your antenna on a car boot or engine cover or wing is dangerous as the RF transmitted can penetrate the glass in the windows and leave you exposed to high levels of radiation, and may also get into the vehicle electronics.
The origin of some of the text on this page is from the RSGB with additions by the web master