Electrical and RF Safety

Electrical Safety

Generators Generators convert mechanical energy to electrical energy. They actually consist of two devices: a gasoline engine and an electrical generator. A generator should be located in a well ventilated area. The installation should be grounded. Extra fuel like gasoline should be stored in a proper storage area.

Generators During a power outage, it is unwise to connect the output of a generator into your home wiring by an ac wall outlet It presents a hazard for electrical workers. You can draw too much current and overload the generator. Power can be restored and can damage the generator.

RF Grounding An RF ground is a physical wire from your station’s equipment to a copper ground rod (8 feet) in the earth. The purpose of a ground wire is to send unwanted signals to ground and not have them radiate. The ground wire must be short and a non resonant length. –If the ground wire is a resonant length at an operating frequency, it will act like an antenna.

RF Grounding Reasons to have a good RF ground: –Reduce electrical noise –Reduce interference –Reduce the possibility of electrical shock

RF Grounding

RF (radio frequency) hot spots can occur in a station located above the ground floor if the equipment is grounded by a long ground wire. The RF exposure limits of the human body are NOT covered in the National Electrical Code. Unintended rectification of an RF signal can cause induced currents in conductors that are in poor electrical contact.

RF Grounding An intermittent RF ground is one cause of severe, broadband radio frequency noise at an Amateur Radio station. A ground loop can be avoided simply by connecting all ground conductors to a single point.

RF Safety It all boils down to common sense: Any radiation at high levels can cause physical harm. –Sunburns –X-rays –Nuclear radiation –Microwaves –Etc.

RF Safety Your new license privileges will allow you greater flexibility but also allow you to operate at frequencies and power levels of increased risk. Common sense: Operate your station properly!

RF Safety Maximum Permissible Exposure (MPE) –Thermal effects (getting cooked) –Athermal effects (cellular and molecular damage)

RF Safety How much power your body will absorb (and in turn heat up) depends on the power density Power density depends on: –Power level where you are –Duty cycle of the wave

RF Safety So – you are required to know about the radiation environment that you create by transmitting so that you do so safely. –Measurements (observations) –Calculations –Tables of data

RF Safety Calculations Two terms of reference: –Field Strength at the location V/m Voltage at distance from antenna –Power density at the location W/m 2 Field strength distributed over surface area at distance from the antenna

Two Formulas