Electrical and RF Safety Electrical Safety Electrical Safety

Electrical and RF Safety

Electrical Safety

Electrical Safety

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 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