Electrical and RF Safety Chapter 9 Electrical and RF Safety Larry Loomer KI6LNB

Brief Review of a few Chapter 8 Exam Questions Why is long distance communication on the 40-meter, 60-meter, 80-meter and 160-meter bands more difficult during the day? The E layer is unstable during daylight hours The D layer absorbs signals at these frequencies during daylight hours The F layer is unstable during daylight hours The F layer absorbs signals at these frequencies during daylight hours The D layer absorbs signals at these frequencies during daylight hours Correct Answer: (C) The D layer absorbs signals at these frequencies during daylight hours [Page 8-4] G3C05 Page 8-4 2017 MDARC/SATERN General Class License Course

Brief Review of a few Chapter 8 Exam Questions What effect does a high sunspot number have on radio communications? Long-distance communication in the upper HF and lower VHF range is enhanced High-frequency radio signals become weak and distorted Microwave communications become unstable Frequencies above 300 MHz become usable for long-distance communication Long-distance communication in the upper HF and lower VHF range is enhanced G3A09 Page 8-6 2017 MDARC/SATERN General Class License Course

Brief Review of a few Chapter 8 Exam Questions What is a characteristic of HF scatter signals? All of these choices are correct They have a wavering sound They have high intelligibility They have very large swings in signal strength They have a wavering sound G3C06 Page 8-11 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety Have an easily accessible master ON/OFF power switch. Don't work on “live” equipment unless absolutely necessary. Never assume equipment is OFF or de-energized --- Check with the meter or tester first. 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety Shocks result from current flowing through the human body. Keep one hand in your pocket. 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety Shocks that result from alternating current (AC) are the most dangerous. The most dangerous currents are those that travel through the heart, such as arm to arm. The next slide shows the effects of electrical current through the body. Use Caution 2017 MDARC/SATERN General Class License Course

2017 MDARC/SATERN General Class License Course Effect 1 second contact 50µA Maximum harmless current. 1mA Faint tingle. 5mA Slight shock felt; not painful but disturbing. Average individual can let go. Strong involuntary reactions can lead to other injuries. 6 – 25 milliamperes (women) Painful shock, loss of muscular control.* 9 – 30 milliamperes (men) 50 – 150 milliamperes Extreme pain, respiratory arrest, severe muscular contractions. Death is possible. 1,000 – 4,300 milliamperes Rhythmic pumping action of the heart ceases. Muscular contraction and nerve damage occur; death likely. 10,000 milliamperes Cardiac arrest, severe burns; death probable. Current Effect 1 second contact * If the extensor muscles are excited by the shock, the person may be thrown away from the power source. Table 9.1, Page 9-3 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety What can we learn from Table 9.1? Consider: The actual amperage of a 9 volt battery depends on the circuit resistance which can be computed using Ohms Law I = E/R 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety The electrical resistance for wet skin is approximately 1,000 ohms. Using Ohm's Law we can compute the amperage resulting from a 9 Volt battery in contact with WET skin to be: I = E/R = 9 volts/1,000 ohms = 9 milliamps. Electrical Shock Based on the information in Table 9-1, what is the likely effect of a 9 V battery on WET skin? 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety Based on Figure 9.3, Page 9-4 Male Female 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety Wire color conventions Hot is Black or Red wire Neutral is the White wire Ground is the Green Wire Properly size the wire being used for the planned electrical load. Is a planned electrical load of 40 amps suitable for a 10 gauge copper wire? Refer to Table 9.2 on Page 9-3 (See the next slide) 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety Is a planned electrical load of 40 amps suitable for a 10 gauge copper wire? Based on Table 9.2, Page 9-3 Copper Wire Size (AWG) Allowable Ampacity (A) Max Fuse or Circuit Breaker 6 55 50 8 40 10 30 12 25 (20)* 20 14 20 (15)* 15 * The National Electrical Code limits the fuse or circuit breaker size (and as such, the maximum allowable circuit load) to 15 A for AWG #14 copper wire and to 20 A for AWG #12 copper wire conductors. 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety Protective Components Based on Table 9.4, Page 9-5 Fuses and Circuit Breakers Fuses and Circuit Breakers should be placed in the HOT wire or wires of an AC circuit. Ground Fault Circuit Interrupter (GFCI) in AC circuits prevents hazards 2017 MDARC/SATERN General Class License Course

Chapter 9 9.1 Electrical Safety Generator Safety Fueling and ventilation operations can pose health hazards. Flammable liquids pose potential health hazards. Use a “Transfer Switch” to connect a generator to home circuits that will not transmit electrical power inadvertently to the utility power grid. 2017 MDARC/SATERN General Class License Course

2017 MDARC/SATERN General Class License Course Chapter 9 9.2 RF Exposure Exposure to RF at low levels is not hazardous, but at high power levels and certain frequencies, RF can be hazardous. Primary factors to consider power level or density frequency average exposure time duty cycle of transmission 2017 MDARC/SATERN General Class License Course

2017 MDARC/SATERN General Class License Course Chapter 9 9.2 RF Exposure Two terms of reference Field Strength at the location (V/m). Voltage at a specific distance from an antenna. Power Density at the location mW/cm2 Field strength distributed over surface area at a distance from the antenna. Absorption and Limits Specific Absorption Rate (SAR) is the best measure of RF exposure for amateur radio operators. Table 9.3 provides the maximum exposure limits. 2017 MDARC/SATERN General Class License Course

Maximum Permissible Exposure (MPE) Limits Uncontrolled Exposure Chapter 9 9.2 RF Exposure Maximum Permissible Exposure (MPE) Limits Controlled Exposure 6-Minute Average Uncontrolled Exposure 30-Minute Average Frequency Range (MHz) Power Density (mW/ 𝒄𝒎 𝟐 ) 0.3 to 3.0 (100)* 3.0 to 30 (900/ 𝒇 𝟐 )* 30 to 300 1.0 300 to 1500 f/300 1,500 to 100,000 5 Frequency Range (MHz) Power Density (mW/ 𝒄𝒎 𝟐 ) 0.3 to 1.34 (100)* 1.34 to 30 (180/ 𝒇 𝟐 )* 30 to 300 0.2 300 to 1500 f/1500 1,500 to 100,000 1.0 * = Plane-wave equivalent power density f = frequency in MHz Based on Table 9.3, Page 9-9 2017 MDARC/SATERN General Class License Course

2017 MDARC/SATERN General Class License Course Chapter 9 9.2 RF Exposure MPE Limits MPE Limits vary with frequency because the body responds differently to the energy at different frequencies. Based on Figure 9.9, Page 9-8 2017 MDARC/SATERN General Class License Course

Averaging and Duty Cycle Chapter 9 9.2 RF Exposure Time Averaging evaluates the total RF exposure over a fixed time interval. Duty Cycle is the ratio of the time the transmitter is on to the total time during the exposure. Controlled Environments refers to people in controlled environments who are considered to be aware of their exposure. Uncontrolled Environments are those areas where the general public has access. Averaging and Duty Cycle 2017 MDARC/SATERN General Class License Course

2017 MDARC/SATERN General Class License Course Chapter 9 9.2 RF Exposure Estimating Exposure and Station Evaluation Station Evaluation Actual measurements of the RF field strength. Use computer modeling for determination. Exposure Determine the Power Density at a known distance and compare with the Maximum Permissible Exposure (MPE). Determine the minimum distance from your antenna where the MPE limit is satisfied. 2017 MDARC/SATERN General Class License Course

2017 MDARC/SATERN General Class License Course Chapter 9 9.2 RF Exposure Estimating Exposure and Station Evaluation Antenna System Consideration must be given to the Gain, including feed line losses, of an antenna because it can influence RF exposure. Exposure Safety Measures Locate or move an antenna away from where people can be exposed to excessive RF fields. Do not point gain antennas where people are likely to be. 2017 MDARC/SATERN General Class License Course

Chapter 9 9.3 Outdoor Safety Antenna Installation Place all antennas and feed lines well clear of power lines. Follow the antenna maker’s instructions for antenna installation. Towers, Masts and Hardware Towers and Masts are used to elevate antennas above buildings and other structures. Towers, Masts and Hardware must be grounded for safety. 2017 MDARC/SATERN General Class License Course

Chapter 9 9.3 Outdoor Safety Performing Antenna and Tower Maintenance Climbers and ground crew should wear appropriate protective gear at all times. The ground crew is an important part of any antenna and tower maintenance team. Secure all electrical and RF equipment. Turn off and unplug all AC equipment, locking the circuits and tagging the circuits if possible. 2017 MDARC/SATERN General Class License Course

Assignment during this week Study your STUDY GUIDE in preparation for the General Class License Exam next week (May 25, 2017). The General Class License Exam will occur in the Salvation Army Fireplace Room (your class room). Your Study Guide 2017 MDARC/SATERN General Class License Course

Please follow the instructions from the Elmers for this room set up. 2017 MDARC/SATERN General Class License Course