RF 1 Flashcards
extremely low frequency (ELF)
30-300 Hz
voice frequency (VF)
300 Hz - 3.3 kHz (intelligible audio)
very low frequency (VLF)
3-30 kHz
low frequency (LF)
30-300 kHz
medium frequency (MF)
300 kHz - 3 MHz
high frequency (HF)
3-30 MHz
very high frequency (VHF)
30-300 MHz
ultra high frequency (UHF)
300 MHz - 3 GHz
super high frequency (SHF)
3-30 GHz
extra high frequency (EHF)
30-300 GHz
human hearing range (audible range)
20 Hz - 20 KHz
Communications System
1) Transmitter
2) Information
3) Channel or Medium
4) Receiver
Communications System Model (Channel/Medium)
1) Most easily intercepted
2) Susceptible to noise and interfering signals
3) Deteriorates over the distance that it travels
4) Usually in an uncontrolled or unprotected space
Communications System Model (Receiver)
1) Easiest to control
2) Located at an unknown listening post
3) Can be specifically designed to match the transmitting requirements
simplex signal
1) One-way
2) Information flows in only one direction
3) Examples: commercial radio and TV, remote controls, GPS, or radio astronomy
duplex signal
1) Two-way
2) Information can flow in both directions
3) Two types: half and full
4) Half duplex only allows one transmitter to communicate at a time, i.e. walkie-talkie
5) Full duplex allows both listening and hearing, i.e. telephone
Analog
1) A continuously varying voltage or current
2) A sine wave is a typical analog signal
3) Ex: voice and video signals
4) Analog and digital can be converted back and forth by an AD Converter and then a DA Converter
Digital
1) A broad term used to describe a signal that sends information by changing discrete values of a wave or from on and off values
2) A pulse is a typical digital signal
3) Ex: HDTV and ASCII Text
4) Digital is replacing analog as bulk of communications
Baseband
Placing the original voice, data, or information directly into the medium without the use of a carrier frequency
Modulation
1) The Process of putting information onto a high frequency carrier for transmission
2) In order to be used by the receiving person it must be DEMODULATED (stripping away the carrier)
3 parameters of a sine wave which can be altered to carry information
1) Amplitude modulation (AM)
2) Frequency modulation (FM)
3) Phase modulation
Types of Internal Noise
1) Thermal
2) White
3) Pink
Thermal Noise
Internal noise caused by thermal interaction between free electrons and vibrating ions in a conductor. (Also known as Johnson-Nyquist Noise)
White Noise
Noise whose frequency content is equal accross the spectrum; prevalent throughout the entire spectrum.
Pink Noise
Noise whose frequency is proportional around a given frequency; prevalent within a portion of the spectrum.
Fast Fourier Transform (FFT)
A technique for converting TIME varying information to its FREQUENCY components.
LC Circuits - Resonance
1) The balanced condition between the inductive and capacitive reactance of a circuit: XL = XC
2) Resonant circuits are the basis of many circuits used to filter and process signals.
LC Oscillator
Oscillating frequency is obtained by specifying capacitor and inductor values to obtain a specific frequency with a tank circuit. (XL = XC)
Crystal Oscillator
A crystal oscillator uses a piezoelectric crystal as the inductive element of an LC circuit. The crystal, usually quartz, is cut to produce a specific frequency. IT IS MORE STABLE THAN AN LC OSCILLATOR.
Best tool to determine if something is working
DMM
Current required to paralyze
> 10 mA
Current required to cause fatal shock
> 100 mA
Number of TIME domains
4; x/y, pos/neg
Number of FREQUENCY domains
2; x/y
General safety rules
1) Don’t work tired
2) Don’t work in poor light
3) Don’t work in wet conditions
4) Don’t wear conductive jewelry
5) Never assume a circuit is dead, always verify
6) Buddy system
7) Don’t mess with safety devices
8) Keep tools clean and in working order
9) Discharge items, such as capacitors, before working on them
10) Don’t mess with safety grounds
11) One-hand rule
12) Use only approved fire extinguishers
13) Follow directions when using chemicals
14) Electronic components may contain hazardous materials
15) Use only approved/equivalent replacement parts
16) Plan, don’t rush
Year Asbestos stopped being used in manufacture of most building products
1979
Asbestos may be found in
Flooring, insulation, fireproofing, roofing, etc.
Greatest radiological threat to a tech
Their own x-ray
Greatest effect on loss
Frequency
Common connectors
1) Type N: < 11 GHz
2) Precision Type N: < 11 GHz; less loss than non-precision
3) Subminiature (SMA): < 18 GHz; less loss than non-precision; easily damaged
4) K (2.92mm): < 40 GHz; easily damaged
5) BNC: < 4 GHz
2 requirements for sound transmission
1) Elasticity
2) Inertia
Speed of sound
1) Air: 344 m/s or 1,129 ft/s
2) Fresh water: 1,480 m/s or 4,856 ft/s
3) Salt water: 1,520 m/s or 4,987 ft/s
4) Wood: 3,360 m/s or 10,991 ft/s
5) Concrete: 3,400 m/s or 11,555 ft/s
6) Steel: 5,050 m/s or 16,568 ft/s
Physical barriers’ effect on sound propagation
1) Reflection
2) Refraction
3) Diffraction
Types of interference
1) Constructive
2) Destructive
Result of 2 sound waves of equal phase, amplitude, and frequency colliding
Resultant amplitude will be doubled
Result of 2 sound waves of equal amplitude and frequency, but 180° out of phase colliding
Result will be 0
Rate of sound drop-off
6 dB per distance doubled
Infrasonic Sound
< 20 Hz
Ultrasonic Sound
> 20 KHz
Flanking Path
When sound travels around (instead of through) an object with little-to-no loss; i.e. gaps under doors, air ducts, etc.
Structure borne audio
When sound couples to the physical structure; i.e. I-beams, pipes, etc.
Sound transmission class (STC)
A barrier transmission loss parameter that determines the effectiveness of a given material or structure to attenuate sound
STC groups
1) Sound Group 1: STC 30 <
2) Sound Group 2: STC 40 <
3) Sound Group 3: STC 45
What type of device is an Oscilloscope?
Time-domain device
O-scope horizontal control
SEC/DIV (x-axis); indicators
O-scope vertical control
VOLT/DIV (y-axis); amplitude and voltage
4 primary sections of an O-scope
1) Vertical
2) Horizontal
3) Trigger
4) Display
Speed of light
300,000,000 m/s
Orthagonal
Right angle
Near field (H)
Magnetic field is more dominant
Far field (E)
Electrical field is more dominant
Separation point of H and E
The 5h point
Range of magnetic field propogation
< 30 MHz
AM Spectrum
535 KHz - 1.7 MHz
FM Spectrum
88 MHz - 108 MHz
Drop off rate of a free field
6 dB per distance doubled
3 primary controls on a Spectrum Analyzer (SA)
1) Reference level (Amplitude)
2) Frequency
3) Span
Factors affecting SA sensativity
1) Noise Floor/MDSL
2) Attenuation
Resolution Bandwidth
1) The narrower the RBW, the finer the resolution, and lower the MDSL
2) As RBW decreases, sweep time increases
Frequency of information (fi)
1) Smaller frequency, greater time
2) Within the sidebands
Frequency of carrier (fc)
Greater frequency, smaller time
2 major characteristics of a receiver
1) Sensitivity
2) Selectivity
SA Intermediate Frequency (IF)
20.4
Dynamic Range
1) The range of signal strengths from the largest to the weakest that a receiver can process
2) Relates to amplitude
3) Does NOT equal frequency
Noise Figure
1) The amount of internal noise added by the receiver
2) Determined by the manufacturer
Types of AM transmission
1) AMDSB
2) AMDSB-SC
3) SSB
4) SSB-SC
5) ISB
6) Vestigial
7) AMCSSB
Suppressed Carrier (SC)
1) Filtering is used to reduce carrier so all power amplification goes to SB during transmission
2) Requires reinsertion of carrier for recovery. Typically provided by the Beat Frequency Oscillator (BFO).
