From charlesreid1

Section 9.1: Electrical Safety

  • Most radio equipment gets power from AC grid

Basic safety:

  • Master onn-off switch
  • Switch shoudl be clearly labeled
  • Don't work on live equipment
  • Don't work alone on energized equipment
  • Don't assume equipment is off (check with meter)
  • Don't activate transmitter or amplifier while working on feed lines/antennas
  • keep one hand in pocket while probing/testing energized equip
  • wear insulated sole shoes, no jewelry
  • Remove, insulate, or secure loose wires and cables
  • Residual charges on capacitors can present hazardous voltages, use bleeder resistors
  • Use grounding stick to remove capacitor charges
  • Ensure exposed conductors are at ground potential

Electrical shocks:

  • Result from electrical flow through body
  • Not voltage, but current that causes shock
  • Shocks of more than 5 mA can be painful
  • Most dangerous currents are arm-to-arm or arm-to-foot
  • Low frequency current (50-60 Hz like household AC) is most dangerous because it can disrupt the heart
  • after shock, heart may resynchronize to usual rythm, enter uncoordinated state called fibrillation, or stop beating algtogether
  • Voltages < 30 V can cause enough current flow to be dangerous
  • Unconsciousness requires CPR

Wiring and safety grounding

  • NEC describes how to handle AC wiring safely
  • Building Codes also important to follow
  • AC wiring: sue standard color conventions
    • Hot - carries voltage - red or black wire, brass terminal
    • Neutral = white wire, silver terminal
    • Ground = green wire, green or bare copper terminal
  • Always connect ground wire to metal chassis to prevent hazardous voltages on equipment
  • Don't use piping as ground unless you have verified it is an effective ground rod
  • Use cable sufficiently rated for current load (ampacity)
  • Most common (household): 12 gauge (20 Amps), 14 gauge (15 Amps)

Protective components:

  • Prevent electrical damage on safety hazards
  • Power control devices: fuses, circuit breakers

Fuses/circuit breakers:

  • Fuses put thin metal between 2 points, metal melts under extreme loads
  • Fuses rated too low can arc (don't use 12 V fuse in 120/240 V circuit)
  • Circuit breakers act as trip, open circuits - these can also be reset
  • Never put fuse/breaker on neutral or ground circuits
  • Never replace fuse/circuit breakers with larger rated one - FIX THE PROBLEM
  • Household: red and black each 120 V, for 240 V total, appliances use separate ground and neutral wires, 4 cables total.

Shock prevention:

  • Safety interlock is shock prevention device
  • Prevents dangerous voltages/intense RF from being present when cabinet/enclosure open
  • One interlock type disconnects high voltage when activated
  • Another type shorts/grounds high voltage when activated
  • GFCI (ground fault circuit interruptor) used in AC circuits
  • Trips if imbalance detected in currents carried by hot and neutral conductors (e.g., bathroom plug)

Generator safety:

  • portable source of electricity, usually gas/diesel/propane
  • Fueling/ventilation is critical for safety
  • Install outdoors, avoid CO buildup
  • When using generator, install CO detector alarms
  • SHut off generators before refueleling to avoid fire
  • Refuel in team of 2, one refuellingand one with fire extinguisher
  • Store furel away from generator and hot exhaust
  • Metal frame of generator not connected to ground, so use grounding rod
  • If generator used at home, careful connecting to home circuit
  • To connect home circuit to generator, disconnect from power grid
  • Open "main" breakers at home to disconnect home from elec. grid
  • Connecting generator to house without disconnecting from grid (back-feeding) can cause large, lethal voltages on utility lines (transformers step them up), dangerous for utility workers and neighbors
  • If power is restored, can damage generator if connected to utility lines
  • Use transfer switch to switch source


  • Provide fire prevention and reduce electrical damage via lightning prevention
  • Disconnect cables and unplug equip. power cords before storm
  • AC power lines, telephone, network wires all conductors
  • Metal entry panel to house where signal/control cables enter is good lightning ground location
  • Panel should be grounded to nearby ground rod with short, heavy metal strap
  • Connect ground rod to AC service entry ground rod with heavy bonded conductor
  • ground wires/straps: as short and direct as possible
  • Towers, masts, antennas mounts should all be grounded
  • Lightning rods should be bonded to other safety grounds
  • Don't use solder - will melt
  • Mechanical clamps, brazing, or welding
  • Determine if homeowners insurance covers lightning damage
  • Coverage of external structures

Section 9.1 Summary

  • With 4 conductor wire in 240 V AC equipment, connect to fuse/circuit breakers with the two hot wires
  • minimum wire size to carry 20 A circuit is 12 gauge wire
  • For circuit using 14 gauge wire, use a fuse/breaker rated to 15 Amps
  • Don't place gas-powered generator in occupied area b/c of danger of CO poisoning
  • GFCI will disconnect 120/240 V power if current flows from one or more hot wires to ground wire
  • Metal enclosure of station equipment should be grounded to ensure hazardous voltages do not appear on chassis
  • Soldered joints should not be used with system connecting to grounding rods because soldered joints will melt and be destroyed
  • Lead-tin solder can contaminate if hands not washed after soldering
  • Good practice for lightning protection grounds is to bond together with all other grounds
  • Purpose of power supply interlock is to ensure dangerous voltages are removed if equipment is opened/worked on
  • When powering home from emergency generator, disconnect incoming utility grid feed
  • NEC covers electrical safety in the ham shack
  • Emergency generator installation shoudl be in a well-ventilated area (risk of CO poisoning)

Section 9.2: RF Exposure

  • Low levels of RF exposure not haazardous
  • At high levels, can be hazardous
  • There are several factors to consider: power level and density, avg exposure time, duty cycle of transmitter
  • Primary factors affecting absorption of RF by body are power density and frequency

Power density

  • Body tissue absorbs RF and heats up
  • RF intensity is power density (mW/cm%2)
  • Power density is highest near antennas and in direction of highest gain
  • Rate of absorption of RF energy is specific absorption rate (SAR)
  • SAR is best measure of RF exposure to ham operators
  • Depends on frequency and body part
  • Limbs and torso ahve highest resonance (most affected) by energy at 30-300 MHz
  • Head most affected by RF at 300 MHz - 3 GHz
  • Eyes most affected by RF at 1+ GHz
  • Frequencies with highest SAR are 30-1500 MHz
  • Safe levels of SAR established by FCC in form of MPE (maximum permissible exposure) limits
  • Vary with frequency

Averaging/Duty Cycle

  • Exposure to RF limited over time interval
  • Time-averaging: total RF exposure over interval

Controlled vs uncontrolled:

  • Controlled - aware of environment and exposure, take reasonable steps to limit exposure
  • Transmitting facilities and near antennas
  • Restricted access
  • Uncontrolled - accessible by general public, unaware of exposure, less likely to receive continuous exposure (so density limits are higher)
  • Averaging period:
    • Controlled: 6 minutes
    • Uncontrolled: 30 minutes

Duty cycle:

  • Ratio of TX time on to total time during exposure
  • Lower transmission duty cycles lead to lower average exposure
  • lower transmission duty cycles permit greater short term exposure levels
  • Operating duty cycle usually 50% or less
  • Different modes have different duty cycles
  • SSB (no speech proc.) has emissions duty cycle of 20%
  • FM (constant power mode) has emissions duty cycle of 100%
  • To get average power output:
    • (TX PEP) x (Emission Duty Cycle) x (Operating Duty Cycle)
  • Example calculation:
    • SSB, no spech proc., TX/RX for equal times, PEP of 150 W:
    • (150 W) x (20 %) x (50 %) = 15 W
  • Example calculation:
    • Station sending SSB AFSK, listening 1/4 of the time, at 100 W PEP:
    • (100 W) x (100% emissions duty cycle) x (75% operating duty cycle) = 75 W

Angenna gain:

  • antenna gain can also affect average power output
  • Significant feed line losses also affect avg power output
  • Example calculation:
    • 6 dB gain antenna, with SSB, no speech processing, TX/RX for equal amt of time, PEP of 150 W:
    • (150 W) x (50%) x (20%) x (6 dB) = 60 W

Estimating exposure/station evaluation:

  • All sations must evaluate capability to cause RF exposure, regardless of power amount
  • LImits of RF exposure must be evaluated, depend on PEP and frequency
  • If power above a certain threshold on a band, must evaluate exposure caused by it
  • Measure RF field strength using calibrated field strenght meters and antennas
  • Easiest to use ARRL tables or online calculator
  • Requires knowing: power at antenna, duty cycel, feed line losses, antenna gain, antenna height, oeprating frequency
  • 2 ways to determine exposure:
    • 1 - determine power density at a known distance
    • 2 - determine minimum distance from antenna at which MPE limit is satisfied
  • If changes made, must re-evaluate unless power output reduced

Exposure safety measures

  • If evaluation results exceed MPE limits, can take steps:
    • Move antenna away
    • Move peopel away
    • Point antenna away
    • Raise antenna
    • Reduce average power
  • Use dummy load or dummy antenna when testing transmitter
  • Reduce power and duty cycle

Section 9.2 Summary

  • RF energy affects body tissue by heating it
  • Estimating whether RF signal exceeds maximum permissible exposure (MPE) requires knowing ALL of these:
    • Duty cycle
    • Frequency
    • Power density
  • Determine if station complies with FCC RF exposure regulations by doing ALL the following:
    • Calculation based on FCC OET Bulletin 6T
    • Calculations based on computational modeling
    • By measuring with field strength meter equipment
  • Time averaging, for RF radiation exposure calculation, means total RF exposure averaged over a certain time
  • If station evaluation shows RF energy exceeds MPE, take action to prevent human exposure to excessive RF fields
  • When installing ground-mounted antenna, install in a way that prevents unauthorized access
  • When evaluating RF exposure, transmitter duty cycle has effect of: lower transmitter duty permits greater short term exposure levels
  • To comply with RF exposure safety regulations in FCC Part 97.13, amateurs must perform routine RF exposure evaluation
  • To accurately measure RF field, use a calibrated field strength meter with a calibrated antenna
  • If evaluation shows neighbor might receive more than an MPE of RF from main lobe of directional antenna, can take precautions to ensure antenna not pointed in their direction
  • If installing indoor transmitting antenna, ensure MPE limits not exceeded in occupied areas

Section 9.3: Outdoor Safety

  • Place all antennas and feed lines clear of power lines
  • 10 feet or more in distance
  • Spearate all parts of antenna and support from power lines at least 150% of total height of mast/height
  • Keep clear and follow manufacturer's specifiations and directions

Antenna/tower maintenance:

  • Before climbing or starting, run through safety checklist
  • Inspect tower guying and support hardware
  • fully rested/blocked (crank-up towers)
  • double-check belts/lanyards
  • inspect load-bearing equipment like pulleys
  • Secure all electrical and RF equipment
    • TX off, disconnected from feed line
    • Unplug all AC equipment, lock circuits out and tag them
    • Check the weather

Be sure gear is secure

  • Belts and harnesses within service life and adequately rated
  • Carabiners closed
  • Safety lanyard and redundant lanyards
  • Follow manufacturer's directions

Section 9.3 Summary

  • Whenever making adjustments or repairs to an antenna, turn off transmitter and disconnect feed line
  • When climbing a tower using a safety belt, confirm belt is rated for weight and within its service life
  • When climbing a tower supporting electrically powered devices, ensure circuits that supply power are locked out and tagged out.