General/Chapter 9 Study Guide - Revision history

Admin: /* Flags */

2016-07-15T18:11:53Z

Flags

← Older revision		Revision as of 18:11, 15 July 2016
Line 236:		Line 236:
	* When climbing a tower supporting electrically powered devices, ensure circuits that supply power are locked out and tagged out.		* When climbing a tower supporting electrically powered devices, ensure circuits that supply power are locked out and tagged out.

	=Flags=		==Flags==

	{{GeneralFlag}}		{{GeneralFlag}}

Admin: /* Section 9.3 Summary */

2016-07-15T18:11:43Z

Section 9.3 Summary

← Older revision		Revision as of 18:11, 15 July 2016
Line 235:		Line 235:
	* When climbing a tower using a safety belt, confirm belt is rated for weight and within its service life		* 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.		* When climbing a tower supporting electrically powered devices, ensure circuits that supply power are locked out and tagged out.

			=Flags=

			{{GeneralFlag}}

Admin: /* Section 9.2: RF Exposure */

2016-07-15T18:11:29Z

Section 9.2: RF Exposure

← Older revision		Revision as of 18:11, 15 July 2016
Line 143:		Line 143:
	* Ratio of TX time on to total time during exposure		* Ratio of TX time on to total time during exposure
	* Lower transmission duty cycles lead to lower average 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.

Admin: Created page with "==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 li..."

2016-07-15T17:58:11Z

Created page with "==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 li..."

New page

==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

Lightning:
* 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