Chapter 10 Topics in Radio Propagation

Chapter 10 Topics in Radio Propagation

Solar Effects Flux and Flares.
Energy from sun that most effects propagation is in the extreme ultra-violet (EUV) spectrum. angstroms ( nm). EUV light is completely absorbed by the upper atmosphere creating the ionosphere. Satellites photograph sun at various wavelengths to determine solar activity. Images are labeled by wavelength. e.g. – 304A indicates 304 angstroms (30.4 nm).

Solar Effects Flux and Flares. Solar flare
A sudden emission of an extremely large amount of energy from the surface of the sun across a broad spectrum of frequencies. The UV & X-ray energy emitted can cause instabilities in the earth’s geomagnetic field.

Solar Effects

Solar Effects Flux and Flares. Solar flare classification
Solar flares are classified according to the amount of x-ray radiation. A-class = Barely discernable -- No impact on propagation. B-class = Weak -- No impact on RF propagation. C-class = Minor – Little impact on RF propagation. M-class = Medium -- Brief radio blackouts, especially near polar regions. X-class = Large -- Planet-wide radio blackouts X1, X2, X3, etc. – Each number doubles the intensity of the radiation.

Solar Effects Geomagnetic Field.
Solar energy & charged particles from the sun deposit energy into the ionosphere and also into the earth’s geomagnetic field. For good propagation, geomagnetic field needs to be stable. Especially at higher latitudes (auroral zones). A geomagnetic storm is occurring when the geomagnetic field is disturbed (unstable).

The following parameters are used to evaluate propagation conditions: BZ K-Index A-Index G-Index

BZ – Intensity & orientation of the interplanetary magnetic field (IMF). If BZ is negative, then the IMF is aligned north-to-south (southward), making it easier for disruptions to occur.

K-index – A measure of the short-term stability of the geomagnetic field. Measures stability over a 3-hour period. Calculated from how much the geomagnetic field intensity varies over the 3-hour period. Measurements from 13 different locations around the world are averaged to arrive at the K-index value.

A-index – A measure of the long-term stability of the geomagnetic field. Measures stability over a 24-hour period. Calculated from the previous 8 K-index values.

Extremely Severe Storm
Solar Effects K-Index Values Inactive 1 Very Quiet 2 Quiet 3 Unsettled 4 Active 5 Minor Storm 6 Major Storm 7 Severe Storm 8 Very Severe Storm 9 Extremely Severe Storm A-Index Values 0-7 Quiet 8-15 Unsettled 16-29 Active 30-49 Minor Storm 50-99 Major Storm Severe Storm

G-Index – A measure of geomagnetic “storminess”. Based on the A & K indices. G-Index Values Quiet 1 Minor 2 Moderate 3 Strong 4 Severe 5 Extreme

E3C02 -- What is indicated by a rising A or K index?
Increasing disruption of the geomagnetic field Decreasing disruption of the geomagnetic field Higher levels of solar UV radiation An increase in the critical frequency

E3C04 -- What does the value of Bz (B sub Z) represent?
Geomagnetic field stability Critical frequency for vertical transmissions Direction and strength of the interplanetary magnetic field Duration of long-delayed echoes

E3C05 -- What orientation of Bz (B sub z) increases the likelihood that incoming particles from the Sun will cause disturbed conditions? Southward Northward Eastward Westward

E3C07 -- Which of the following descriptors indicates the greatest solar flare intensity?
Class A Class B Class M Class X

E3C08 -- What does the space weather term G5 mean?
An extreme geomagnetic storm Very low solar activity Moderate solar wind Waning sunspot numbers

E3C09 -- How does the intensity of an X3 flare compare to that of an X2 flare?
10 percent greater 50 percent greater Twice as great Four times as great

E3C10 -- What does the 304A solar parameter measure?
The ratio of X-Ray flux to radio flux, correlated to sunspot number UV emissions at 304 angstroms, correlated to solar flux index The solar wind velocity at 304 degrees from the solar equator, correlated to solar activity The solar emission at 304 GHz, correlated to X-Ray flare levels

HF Propagation In nearly all cases, HF waves travel along the surface of the earth or they are returned to earth after encountering the upper layers of the ionosphere.

HF Propagation All types of waves can change direction due to two different phenomena: Diffraction. Encountering a reflecting surface’s edge or corner. Refraction. Change in velocity due to change in properties of medium wave is traveling through.

HF Propagation Ground-Wave Propagation Special type of diffraction.
Lower edge of wave (closest to the earth) loses energy due to induced ground currents. Lower edge slows, tilting wave front forward. Primarily effects vertically-polarized waves. Most noticeable on longer wavelengths. AM broadcast, 160m, & 80m.

HF Propagation Ground-Wave Propagation
As a ground wave signal travels along the surface of the earth, it is absorbed, decreasing its strength. Absorption is more pronounced at shorter wavelengths. At 28 MHz, only useful up to a few miles. Most useful during daylight on 160m & 80m. Useful for communications between miles.

E3C12 -- How does the maximum distance of ground-wave propagation change when the signal frequency is increased? It stays the same It increases It decreases It peaks at roughly 14 MHz

E3C13 -- What type of polarization is best for ground-wave propagation?
Vertical Horizontal Circular Elliptical

HF Propagation Skywave Propagation
Radio waves refracted in the E & F layers of the ionosphere. Maximum one-hop skip distance about 2500 miles.

When a radio wave enters the ionosphere, it splits into 2 waves polarized at right-angles to each other. Ordinary wave (o-wave) – E-field parallel to Earth’s magnetic field. Extraordinary wave (x-wave) – E-field perpendicular to Earth’s magnetic field. O-wave & x-wave recombine to form an elliptically polarized wave.

HF Propagation Skywave Propagation Chordal wave propagation.
Radio waves can become “trapped” in the ionosphere. Refracted between the F & E layers or within the F layer. Long distances without losses from reflecting off earth.

HF Propagation Skywave Propagation

Voice of America Coverage Analysis Program (VOACAP). Software designed by the VOA to predict HF propagation between 2 points. Software can show that a radio wave can take more than one path between 2 points. Ray tracing – following the various paths the wave may take.

HF Propagation Skywave Propagation Absorption. D layer.
Ionized only during sunlight. Absorbs RF energy. The longer the wavelength, the more absorption. Kills sky wave propagation on 160m & 80m during daylight hours.

HF Propagation Skywave Propagation Absorption.
Geomagnetic disturbances & solar flares increase absorption. As A & K indices rise, absorption increases. Noise level increases as signals decrease. More pronounced for paths over the polar regions.

E3B04 -- What is meant by the terms extraordinary and ordinary waves?
Extraordinary waves describe rare long skip propagation compared to ordinary waves which travel shorter distances Independent waves created in the ionosphere that are elliptically polarized Long path and short path waves Refracted rays and reflected waves

E3B12 -- What is the primary characteristic of chordal hop propagation?
Propagation away from the great circle bearing between stations Successive ionospheric reflections without an intermediate reflection from the ground Propagation across the geomagnetic equator Signals reflected back toward the transmitting station

E3B13 -- Why is chordal hop propagation desirable?
The signal experiences less loss along the path compared to normal skip propagation The MUF for chordal hop propagation is much lower than for normal skip propagation Atmospheric noise is lower in the direction of chordal hop propagation Signals travel faster along ionospheric chords

E3B14 -- What happens to linearly polarized radio waves that split into ordinary and extraordinary waves in the ionosphere? They are bent toward the magnetic poles Their polarization is randomly modified They become elliptically polarized They become phase-locked

E3C01 -- What does the term ray tracing describe in regard to radio communications?
The process in which an electronic display presents a pattern Modeling a radio wave's path through the ionosphere Determining the radiation pattern from an array of antennas Evaluating high voltage sources for X-Rays

E3C03 -- Which of the following signal paths is most likely to experience high levels of absorption when the A index or K index is elevated? Transequatorial propagation Polar paths Sporadic-E NVIS

E3C11 -- What does VOACAP software model?
AC voltage and impedance VHF radio propagation HF propagation AC current and impedance

E3C15 -- What might a sudden rise in radio background noise indicate?
A meteor ping A solar flare has occurred Increased transequatorial propagation likely Long-path propagation is occurring

HF Propagation Long Path and Gray Line Propagation Long path.
Radio waves travel a great-circle path between 2 stations. The path is shorter in one direction & longer in the other. The normal path is the shorter. The long path is 180° from the short path.

HF Propagation Long Path and Gray Line Long path.
A slight echo on the received signal may indicate that long-path propagation is occurring. With long path propagation, the received signal may be stronger if antenna is pointed 180° away from the station. Long path propagation can occur on all MF & HF bands. 160m through 10m. Most often on 20m.

HF Propagation Long Path vs. Short Path

HF Propagation Long Path and Gray Line Gray line propagation.
At sunset: D layer collapses rapidly, reducing adsorption. F layer collapses more slowly. At sunrise: D layer doesn’t start forming until sun well above horizon. F layer starts ionizing at first light. Net result is that long distance communications are possible during twilight hours on the lower frequency bands. 8,000 to 10,000 miles. 160m, 80m, 40m, & possibly 30m.

HF Propagation Long Path and Gray Line Gray line propagation.

E3B05 -- Which amateur bands typically support long-path propagation?
160 meters to 40 meters 30 meters to 10 meters 160 meters to 10 meters 6 meters to 2 meters

E3B06 -- Which of the following amateur bands most frequently provides long-path propagation?
80 meters 20 meters 10 meters 6 meters

E3B07 -- Which of the following could account for hearing an echo on the received signal of a distant station? High D layer absorption Meteor scatter Transmit frequency is higher than the MUF Receipt of a signal by more than one path

E3B08 -- What type of HF Propagation is probably occurring if radio signals travel along the terminator between daylight and darkness? Transequatorial Sporadic-E Long-path Gray-line

E3B10 -- What is the cause of gray-line propagation?
At midday, the Sun super heats the ionosphere causing increased refraction of radio waves At twilight and sunrise, D-layer absorption is low while E-layer and F-layer propagation remains high In darkness, solar absorption drops greatly while atmospheric ionization remains steady At mid-afternoon, the Sun heats the ionosphere decreasing radio wave refraction and the MUF

VHF/UHF/Microwave Propagation
Above 30 MHz, radio waves are rarely refracted back to earth by the ionosphere. Must use other techniques for long-distance communications. Low-angle of radiation from the antenna is more important than on HF. It is more important for polarization of transmitting & receiving antennas to match than on HF.

Radio Horizon Radio horizon not the same as visual horizon. Refraction in the atmosphere bends radio waves & increases “line-of-sight” distance by about 15%. Visual Horizon (miles) ≈ Hft Radio Horizon (miles) ≈ Hft Caused by variations in density of atmosphere.

Multipath Radio waves reflected off of many objects arrive at receive antenna at different times. Waves reinforce or cancel each other depending on phase relationship. Picket fencing.

E3C06 -- By how much does the VHF/UHF radio-path horizon distance exceed the geometric horizon?
By approximately 15% of the distance By approximately twice the distance By approximately one-half the distance By approximately four times the distance

E3C14 -- Why does the radio-path horizon distance exceed the geometric horizon?
E-region skip D-region skip Downward bending due to aurora refraction Downward bending due to density variations in the atmosphere

Tropospheric Propagation VHF/UHF/Microwave Propagation normally limited to about 50 miles. Temperature inversions can create a “duct” where radio waves can travel for long distances. miles. More common over water. Hepburn maps show where conditions exist to support tropospheric ducting.

Tropospheric Propagation

Tropospheric Propagation Other types of “tropo” include scattering off of precipitation. Precipitation must be within line-of-sight range of both stations.

E3A04 -- What do Hepburn maps predict?
Sporadic E propagation Locations of auroral reflecting zones Likelihood of rain-scatter along cold or warm fronts Probability of tropospheric propagation

E3A05 -- Tropospheric propagation of microwave signals often occurs along what weather related structure? Gray-line Lightning discharges Warm and cold fronts Sprites and jets

E3A06 -- Which of the following is required for microwave propagation via rain scatter?
Rain droplets must be electrically charged Rain droplets must be within the E layer The rain must be within radio range of both stations All of these choices are correct

E3A07 -- Atmospheric ducts capable of propagating microwave signals often form over what geographic feature? Mountain ranges Forests Bodies of water Urban areas

E3A10 -- Which type of atmospheric structure can create a path for microwave propagation?
The jet stream Temperature inversion Wind shear Dust devil

E3A11 -- What is a typical range for tropospheric propagation of microwave signals?
10 miles to 50 miles 100 miles to 300 miles 1200 miles 2500 miles

Sporadic E Propagation Refraction by temporary, highly-ionized areas in the E layer. 10m. 6m. 2m. Allows contacts form 300 to 1200 miles. Can last for a few minutes or several hours.

Sporadic E Propagation Can occur any time of day or night. Can occur any time of the year, but most common near the summer & winter solstices. Best during May, June & July.

E3B09 -- At what time of year is Sporadic E propagation most likely to occur?
Around the solstices, especially the summer solstice Around the solstices, especially the winter solstice Around the equinoxes, especially the spring equinox Around the equinoxes, especially the fall equinox

E3B11 -- At what time of day is Sporadic-E propagation most likely to occur?
Around sunset Around sunrise Early evening Any time

Transequatorial Propagation Communications between stations located an equal distance north & south of the magnetic equator.

Transequatorial Propagation Most prevalent around the spring & autumn equinoxes. Maximum effect during afternoon & early evening. Allows contacts up to about 5,000 miles. Useable up to 2m & somewhat on 70cm. As frequency increases, paths more restricted to exactly equidistant from and perpendicular to the magnetic equator.

E3B01 -- What is transequatorial propagation?
Propagation between two mid-latitude points at approximately the same distance north and south of the magnetic equator Propagation between any two points located on the magnetic equator Propagation between two continents by way of ducts along the magnetic equator Propagation between two stations at the same latitude

E3B02 -- What is the approximate maximum range for signals using transequatorial propagation?
1000 miles 2500 miles 5000 miles 7500 miles

E3B03 -- What is the best time of day for transequatorial propagation?
Morning Noon Afternoon or early evening Late at night

Auroral Propagation

Auroral Propagation Charged particles from the sun (solar wind) are concentrated over the magnetic poles by the earth’s magnetic field & ionize the E-layer. VHF & UHF propagation up to about 1,400 miles.

Auroral Propagation Reflections change rapidly. All signals sound fluttery. SSB signals sound raspy. CW signals sound like they are modulated with white noise. CW most effective mode. Point antenna toward aurora, NOT towards station. In US, point antenna north.

E3A12 -- What is the cause of Aurora activity?
The interaction in the F2 layer between the solar wind and the Van Allen belt A low sunspot level combined with tropospheric ducting The interaction in the E layer of charged particles from the Sun with the Earth’s magnetic field Meteor showers concentrated in the extreme northern and southern latitudes

E3A13 -- Which emission mode is best for aurora propagation?
CW SSB FM RTTY

E3A14 -- From the contiguous 48 states, in which approximate direction should an antenna be pointed to take maximum advantage of aurora propagation? South North East West

Meteor Scatter Communications Meteors passing through the ionosphere collide with air molecules & strip off electrons. Ionization occurs at or near the E-region. 50-75 miles above the earth. Best propagation on 28 MHz to 148 MHz. 20 MHz to 432 MHz possible.

Meteor Scatter Communications Major meteor showers. Quadrantids – January 3-5. Lyrids – April Arietids – June 8. Aquarids – July Perseids – July 27 to August 14. Orionids – October Taurids – October 26 to November 16. Leonids – November Geminids – December Ursids – December 22.

Meteor Scatter Communications Operating techniques. Keep transmissions SHORT. Divide each minute into four 15-second segments. Stations at west end of path transmit during 1st & 3rd segments. Stations at east end of path transmit during 2nd & 4th segments.

Meteor Scatter Communications Operating techniques. Modes: HSCW. 800-2,000 wpm. Computer generated & decoded. FSK441 (part of WSJT software suite). Repeated short bursts of data.

E2D02 -- Which of the following is a good technique for making meteor scatter contacts?
15 second timed transmission sequences with stations alternating based on location Use of high speed CW or digital modes Short transmission with rapidly repeated call signs and signal reports All of these choices are correct

The E layer The F1 layer The F2 layer The D layer
E3A08 -- When a meteor strikes the Earth's atmosphere, a cylindrical region of free electrons is formed at what layer of the ionosphere? The E layer The F1 layer The F2 layer The D layer

E3A09 -- Which of the following frequency ranges is well suited for meteor-scatter communications?
MHz MHz MHz MHz

Earth-Moon-Earth (EME) Communications. a.k.a. – Moon bounce. If both stations can “see” the moon, they can talk. Maximum about 12,000 miles. Best when moon is at perigee. 2 dB less path loss. Not useable near new moon. Increased noise from the sun. The higher the moon is in the sky the better.

Earth-Moon-Earth (EME) Communications. Low receiver noise figure essential. Libration Fading. Caused by multipath effects of rough moon surface in combination with relative motion between the earth and the moon. Rapid, deep, irregular fading. 20 dB or more. Up to 10 Hz. Can cause slow-speed CW to sound like high-speed CW.

Earth-Moon-Earth (EME) Communications. 2m operation. MHz to MHz. 2-minute schedule. Transmit for 2 minutes. Receive for 2 minutes. Station farthest east transmits first then station to the west.

Earth-Moon-Earth (EME) Communications. 70cm operation. MHz to MHz. 2.5-minute schedule. Transmit for 2.5 minutes Receive for 2.5 minutes. Station farthest east transmits first then station to the west.

E2D06 -- Which of the following describes a method of establishing EME contacts?
Time synchronous transmissions alternately from each station Storing and forwarding digital messages Judging optimum transmission times by monitoring beacons reflected from the Moon High speed CW identification to avoid fading

E3A01 -- What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by Moon bounce? 500 miles, if the Moon is at perigee 2000 miles, if the Moon is at apogee 5000 miles, if the Moon is at perigee 12,000 miles, if the Moon is visible by both stations

E3A02 -- What characterizes libration fading of an EME signal?
A slow change in the pitch of the CW signal A fluttery irregular fading A gradual loss of signal as the Sun rises The returning echo is several Hertz lower in frequency than the transmitted signal

E3A03 -- When scheduling EME contacts, which of these conditions will generally result in the least path loss? When the Moon is at perigee When the Moon is full When the Moon is at apogee When the MUF is above 30 MHz

Questions?

Chapter 11 Safety

Hazardous Materials PCB’s Polychlorinated Biphenyls.
Not printed circuit boards. Additive to oils used as insulator in older electrical components. Large transformers. High-voltage capacitors. Known carcinogen.

Hazardous Materials PCB’s Avoid skin contact.
Wear rubber gloves Wipe down case with paper towel. Properly dispose of component & materials used to handle it.

Hazardous Materials Beryllium and Beryllium Oxide
Beryllium (Be) alloyed with copper to stiffen it & improve conductivity. Spring contacts. Beryllium Oxide (BeO) is a ceramic used as insulator inside vacuum tubes & semiconductors. Not dangerous in solid form. Known carcinogen if crushed & dust is inhaled.

Hazardous Materials Lead and Soldering
Common solder is alloy of lead and tin. Dangers from lead are: Inhaling lead vapors -- NOT. Temperatures involved in soldering not high enough to create lead vapor. Fumes/vapors created during soldering caused by burning flux. Ingestion. Wash hands thoroughly before handling food.

Hazardous Materials Carbon Monoxide (CO)
Colorless, odorless, tasteless gas. Generated by incomplete combustion of fuels. Can ONLY be detected by a carbon monoxide detector. Ordinary smoke detectors will NOT detect CO gas.

Hazardous Materials Carbon Monoxide (CO)
Generators & fossil fuel heaters must only be used in open, well-ventilated areas. Fuel must not be stored by the generator or heater. Install carbon monoxide detectors in any area occupied by people where CO gas may accumulate.

E0A07 -- How may dangerous levels of carbon monoxide from an emergency generator be detected?
By the odor Only with a carbon monoxide detector Any ordinary smoke detector can be used By the yellowish appearance of the gas

E0A09 -- Which insulating material commonly used as a thermal conductor for some types of electronic devices is extremely toxic if broken or crushed and the particles are accidentally inhaled? Mica Zinc oxide Beryllium Oxide Uranium Hexaflouride

E0A10 -- What toxic material may be present in some electronic components such as high voltage capacitors and transformers? Polychlorinated biphenyls Polyethylene Polytetrafluroethylene Polymorphic silicon

RF Exposure Ionizing and Non-Ionizing Radiation. Ionizing Radiation.
Energy high enough to strip electrons off of atoms or break atoms apart. Radioactive sources. Ultra-violet light. X-rays. Non-ionizing radiation. Insufficient energy to strip electrons off of atoms or break atoms apart. Radio frequency energy.

RF Exposure Ionizing and Non-Ionizing Radiation.

RF Exposure Ionizing and Non-Ionizing Radiation. Power Density.
RF at low levels is not dangerous. Only dangerous when level high enough to cause heating of body tissue. Power Density. Heating is caused by body absorbing RF energy. Intensity of RF energy is called power density. Measured in mW/cm2.

RF Exposure Power Density.
Intensity of electric (E) field & magnetic (H) field can be measured separately. E field measured in V/m. H field measured in A/m. E field & H field can peak at different locations. Field impedance varies due to ground reflections, scattering, & antenna proximity. Z = E / H.

RF Exposure Absorption and Limits. Specific absorption rate (SAR).
Rate at which the body absorbs RF energy. Varies with frequency & size of body part. Range of highest SAR is 30 MHz to 1.3 GHz. Torso & limbs -- SAR highest at VHF (30 MHz to 300 MHz). Head – SAR highest at UHF (300 MHz to 3 GHz). Eyes – SAR highest at microwave frequencies < 1 GHz.

RF Exposure Absorption and Limits. Maximum permissible exposure (MPE).
Highest level of exposure allowed by the regulations.

RF Exposure Averaging and Duty Cycle.
Exposure to RF is averaged over specified time periods. Body responds differently to long duration and short duration exposure. Different “environments” are averaged over different time periods. Controlled environment. Uncontrolled environment.

RF Exposure Averaging and Duty Cycle. Controlled environment.
Areas where occupants are aware of and knowledgeable about RF exposure. Exposure averaged over 6-minute period. Higher MPE limits. Uncontrolled environment. Areas accessible to persons unaware of RF exposure. Exposure averaged over 30-minute period. Lower MPE limits.

RF Exposure Absorption and Limits.

RF Exposure Averaging and Duty Cycle. Duty cycle.
Ratio of transmitter on time to total time during the exposure. Varies with mode. Transmitter is not at full output power all of the time depending on mode. Typical duty cycles: SSB (unprocessed) = 20% to 25%. SSB (processed) = 40%. FM = 100%. CW = 40%.

E0A02 -- When evaluating RF exposure levels from your station at a neighbor’s home, what must you do? Make sure signals from your station are less than the controlled MPE limits Make sure signals from your station are less than the uncontrolled MPE limits You need only evaluate exposure levels on your own property Advise your neighbors of the results of your tests

E0A06 -- Why are there separate electric (E) and magnetic (H) field MPE limits?
The body reacts to electromagnetic radiation from both the E and H fields Ground reflections and scattering make the field impedance vary with location E field and H field radiation intensity peaks can occur at different locations All of these choices are correct

E0A08 -- What does SAR measure?
Synthetic Aperture Ratio of the human body Signal Amplification Rating The rate at which RF energy is absorbed by the body The rate of RF energy reflected from stationary terrain

E0A11 -- Which of the following injuries can result from using high-power UHF or microwave transmitters? Hearing loss caused by high voltage corona discharge Blood clotting from the intense magnetic field Localized heating of the body from RF exposure in excess of the MPE limits Ingestion of ozone gas from the cooling system

RF Exposure Antenna System.
Must take into account antenna gain if in far field. Far field -- antenna pattern does not change with distance. Approximately 10λ.

RF Exposure Estimating Exposure and Station Evaluation.
All fixed amateur stations must evaluate RF exposure potential. Mobile & portable stations exempt. Exempt if transmitter output power is below specified limits. Limits vary by frequency. Only have to evaluate transmitters that exceed the specified power output limits.

Power thresholds for RF Exposure Evaluation. HF VHF/UHF/Microwave 160m, 80m, 40m 500W 6m 50W 30m 425W 2m 20m 225W 1.25m 17m 125W 70cm 70W 15m 100W 33cm 150W 12m 75W 23cm 200W 10m 13cm & up 250W

Methods of Evaluating RF Exposure. Calibrated field strength meter and antenna. VERY expensive. ≈ $15,000.

Methods of Evaluating RF Exposure. Calculate using formulas. Use charts based on formulas. Use software based on formulas. Need to know: Transmitter output power. Feedline loss. Antenna gain. Antenna height above ground. Frequency.

Multi-transmitter environment. All transmitter operators are jointly responsible for seeing that MPE’s are not exceeded. A transmitter must be included in the site evaluation if it produces more than 5% of the MPE for that frequency.

RF Exposure Exposure Safety Measures.
Locate antennas where people cannot get near them. Don’t point antennas at occupied locations. Carefully evaluate exposure from “stealth” antennas.

RF Exposure Exposure Safety Measures.
Locate VHF/UHF mobile antennas on roof of vehicle or on trunk lid. Use extra care with high-gain antennas used for VHF/UHF/microwave frequencies.

E0A03 -- Which of the following would be a practical way to estimate whether the RF fields produced by an amateur radio station are within permissible MPE limits? Use a calibrated antenna analyzer Use a hand calculator plus Smith-chart equations to calculate the fields Use an antenna modeling program to calculate field strength at accessible locations All of the choices are correct

E0A04 -- When evaluating a site with multiple transmitters operating at the same time, the operators and licensees of which transmitters are responsible for mitigating over-exposure situations? Only the most powerful transmitter Only commercial transmitters Each transmitter that produces 5 percent or more of its MPE exposure limit at accessible locations Each transmitter operating with a duty-cycle greater than 50 percent

E0A05 -- What is one of the potential hazards of using microwaves in the amateur radio bands?
Microwaves are ionizing radiation The high gain antennas commonly used can result in high exposure levels Microwaves often travel long distances by ionospheric reflection The extremely high frequency energy can damage the joints of antenna structures

Grounding and Bonding An amateur radio station needs to deal with several types of “grounds”. Electrical safety ground. Lightning protection ground. Common potential ground. a.k.a. – RF ground. All 3 ground systems should be bonded together at a common point.

Grounding and Bonding Electrical Safety Ground.
Intended to prevent electrical shock. Required by National Electrical Code (NEC). a.k.a. -- “3rd-wire” or “green wire” ground.

Grounding and Bonding Lightning Protection Ground.
Intended to prevent damage from lightning striking antenna system. Lightning pulse characteristics: Up to tens of thousands of Ampreres. Low resistance connections required. Has RF components up to about 1 MHz. Low inductance connections required.

Grounding and Bonding Lightning Protection Ground.
The primary purpose of ground rods is to provide lightning protection for both AC power systems and antenna systems.

Grounding and Bonding Common Potential Ground.
Intended to prevent stray RF voltages from interfering with proper operation of station equipment. RF feedback. a.k.a. – RF ground.

E0A05 -- What is the primary function of an external earth connection or ground rod?
Reduce received noise Lightning protection Reduce RF current flow between pieces of equipment Reduce RFI to telephones and home entertainment systems

Questions?

Chapter 10 Topics in Radio Propagation

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