and Direct Current
||Alternating Current and Transformers
||Circuit Protection, Control, and Measurement
||Electrical Conductors, Wiring Techniques,
and Schematic Reading
||Generators and Motors
||Electronic Emission, Tubes, and Power Supplies
||Solid-State Devices and Power Supplies
||Wave-Generation and Wave-Shaping Circuits
||Wave Propagation, Transmission Lines, and
||Introduction to Number Systems and Logic Circuits
||- Introduction to Microelectronics
||Principles of Synchros, Servos, and Gyros
||Introduction to Test Equipment
||Radio-Frequency Communications Principles
||The Technician's Handbook, Master Glossary
||Test Methods and Practices
||Introduction to Digital Computers
||Introduction to Fiber Optics
|Note: Navy Electricity and Electronics Training
Series (NEETS) content is U.S. Navy property in the public domain.
NEETS Module 17 − Radio−Frequency Communications Principles
4−1− to 4−10,
manner that allows RF current to flow through the area of contact. Resistance
of the skin to the current flow at the areas of contact causes heat. The effect
of the heat on a person at the point of contact ranges from noticeable warmth to
a painful burn.
The most useful and widespread technique in the reduction of RF burn hazards
is the proper bonding and grounding of all metallic objects in the RF radiation
In some cases, the RF burn hazard can be eliminated only through the use of restrictive
operating procedures. These procedures govern the simultaneous use of transmitting
and cargo equipment. Techniques such as operation of transmitters at reduced power
and the prohibition of simultaneous use of certain combinations of antennas, frequencies,
and cargo handling equipment are used.
Figure 3-35 shows typical RF radiation hazard warning signs.
Figure 3-35. - Typical RF radiation hazard warning signs.
Most studies on the subject of radiation hazards (RADHAZ) have emphasized the
impact of electromagnetic radiation on man. Man is singled out because of the biological,
thermal, and neurological effects that occur in human organs and other biological
tissues. Certain organs of the body are considered to be more susceptible than others
to the effects of electromagnetic radiation. Presently available information and
experience indicate that the eyes and testes are the most vulnerable body organs.
The overwhelming danger to date appears to be the hazard from thermal effects, which
are a function of intensity of radiation and frequency. This is particularly true
in the range of 1 to 3 gigahertz. Thermal effects appear to taper off in severity
outside this range.
When the body is irradiated by energy from a point source, the total body surface
is usually not exposed. The larger the area exposed and the larger the radiation
power density, the higher the body temperature rise and the greater the hazard.
Microwave radiation from a radar source will "cook" you internally, just as a microwave
oven cooks a chicken.
An injury of great concern is that to the lens of the eye. Exposure of the lens
to high-intensity microwaves may cause cataracts. Current medical evidence indicates
that a significant temperature elevation of the lens is required for cataract formation.
If exposure is limited to 10 milliwatts per centimeter squared, the lens temperature
is not elevated to levels at which cataracts occur.
In addition to thermal effects, nonionizing radiation is known to produce nonthermal
effects. An association of a biological hazard with the nonthermal effects has not
A peculiar effect experienced by some personnel is the sensation of sound when
they are exposed to pulsed microwave fields. This occurs at levels below stated
hazard limits and is not, by itself, considered dangerous.
Q38. Electromagnetic radiation is hazardous to personnel in what
Q39. What is the most useful and widespread technique to reduce RF
Now that you have completed this chapter, a short review of what you have learned
is in order. The following summary will refresh your memory of basic systems equipment,
its principles, terms, and typical circuitry required for you to understand this
A Radio SET CONTROL UNIT is used to remotely control certain
transmitter and receiver functions.
Transmitter Transfer SwitchBOARDS selectively transfer remote
control station functions and signals to transmitters.
RECEIVER Transfer SwitchBOARDS transfer receiver audio outputs
to remote control station audio circuits.
A Transmitter generates an RF carrier, modulates it with intelligence,
amplifies it, and applies it to an antenna.
An Antenna COUPLER is a device used for impedance matching between
an antenna and a transmitter or receiver.
A RECEIVER receives electromagnetic energy (RF) and may convert
it to a visible or audible form.
MULTICOUPLERS patch several receivers or transmitters to one
antenna. They also filter out harmonics and spurious responses, and provide impedance
MARKING is when a circuit is closed and current flows in teletypewriter
operation. SPACING is when a circuit is open and no current flows in teletypewriter
operation. INTELLIGENCE is any signal that conveys information (voice, teletypewriter,
facsimile). a START unit is the first unit of a teletypewriter signal. It is always
A STOP unit is the last unit of a teletypewriter signal. It
is always a mark.
A TRANSITION is the time it takes to shift from a mark to a
space condition or from a space to a mark condition.
A Code in teletypewriter operation is a combination of mark
and space conditions representing symbols, figures, or letters.
NONSYNCHRONOUS teletypewriter operation is when both transmitter
and receiver do not operate continuously.
SYNCHRONOUS teletypewriter operation is when both transmitter
and receiver operate continuously.
WORDS-PER-MINUTE is an approximate rate of speed. It means the
number of five letter words with a space between them that can be transmitted or
received in a one-minute period.
BAUD is a measurement of speed based on the number of code elements
or units per second.
BITS-PER-SECOND is an acronym of the words binary digit. One
bit is equal to one signal unit or element.
NEUTRAL teletypewriter operation is where current flow represents
a mark and no flow represents a space.
POLAR teletypewriter operation is where current flow of one
polarity represents a mark and current of the opposite polarity is a space.
RUNNING OPEN is the teletypewriter condition where the type
hammer constantly strikes the type box but does not print or move across the page.
A KEYER is a device that changes dc pulses to mark and space
modulation for teletypewriter transmissions.
A CONVERTER changes an audio signal back to dc pulses during
Audio Frequency TONE SHIFT systems use amplitude modulation
to change dc mark and space impulses into audio impulses.
Radio Frequency CARRIER SHIFT systems use a keyer to shift a
radio frequency signal above or below an assigned frequency. These shifts correspond
to marks and spaces.
A TELETYPEWRITER is a machine that can transmit and or receive
letters, numbers, or symbols. It may have a keyboard similar to a typewriter.
A PERforATOR is a device that stores a teletypewriter message
on a paper tape by punching Baudot coded messages into it.
Transmitter DIsTRIBUTOR is a device that reads Baudot code from
paper tape and allows a message to be sent or a message to be printed on a page
A REPERforATOR stores an incoming TTY signal on paper tape.
A Page PRINTER prints teletypewriter characters one at a time
in a full-page format. This is usually a high-speed printer.
RED is the reference color of equipment that passes classified
information. It normally refers to patch panels.
BLACK is the reference color of equipment that passes unclassified
information. It normally refers to patch panels.
A PATCH PANEL is used to tie a receiver or transmitter to its
A COMPARATOR compares incoming signals and selects the strongest
to be fed to a teletypewriter through a patch panel. This is used in diversity operation
A LIsSAJOUS Pattern is a combined, simultaneous display of the
amplitude and phase relationships of two input signals on a CRT.
A TONE-TERMINAL set converts TTY dc pulses into audio tones
for modulation of a transmitter in audio-frequency tone shift transmissions.
MULTIPLEXING is the process of transmitting a number of intelligence
signals simultaneously over a single RF carrier.
TIME-DIVIsION multiplexing is the process that periodically
samples several intelligence signals. This can be a received signal or one to be
Frequency-DIVIsION multiplexing transmits and receives the full
360 degrees of each sine wave.
FACSIMILE is the method for transmitting and receiving still
images. These images can be maps, photographs, and handwritten or printed text.
SCANNING is the process of subdividing a picture in an orderly
manner into segments. This is used in facsimile transmission.
FRAMING is the process of synchronizing a facsimile receiver
to a transmitter. This allows proper picture reproduction.
TEMPEST is a term normally used to describe compromising emanations.
These emanations are unintentionally radiated signals that could disclose classified
ELECTROMagnetic INTERFERENCE is a term used to describe the
degradation of a receiver or system by externally produced RF energy.
Answers to Questions Q1. Through Q39.
A1. To convert energy electrical/acoustic to acoustic/electrical
and to key/unkey a transmitter. Also it mutes a receiver when transmitting.
A2. Transferring remote control functions and signals to transmitters.
A3. Transfers receiver audio outputs to remote control stations.
A4. 800 watts.
A5. Automatic, semiautomatic, and manual.
A6. It matches the impedance of an antenna to that of a transmission
line at any desired frequency.
A7. To aid in heat transfer and prevent corona and arcing.
A8. LSB, USB, IsB, AM, CW, FSK.
A10. To connect an antenna/transmission line to a receiver/transmitter.
A11. Patching and filtering and permits the multiple use of receivers
and/or transmitters on a single antenna.
A12. Space and mark.
A13. Intelligence (5), start (1), stop (1).
A14. Shift signals.
A15. Synchronous and nonsynchronous.
A16. a unit of modulation rate.
A17. Binary digit.
A18. Neutral and polar.
A19. Converts dc to corresponding mark and space modulation.
A20. Converts the audio signal to dc pulses.
A21. uses AM to change dc to audio.
A22. a keyer provides RF excitation, which can be shifted above or
below the assigned frequency.
A23. 60, 75, or 100 wpm.
A24. Page-size copy paper and perforated tape.
A25. It handles classified information.
A26. To code or decode messages.
A27. The comparator compares the signal strengths from the receivers
and the converter converts the frequency-shift RF signal into a TTY set dc loop
A28. It converts dc to audio or vice versa.
A29. Time-division and frequency-division.
A30. It allows simultaneous transmission of multiple signals on a
single transmission path.
A32. Compromising emanations.
A33. Reliability, security, and speed.
A35. To ensure continuous, optimum performance of communications
A36. Electromagnetic interference.
A37. Conduction and radiation.
A38. RF burns and biological, thermal, and neurological effects.
A39. Proper bonding and grounding.