RF Signals and Modulation Flashcards
Define frequency.
The number of times a signal makes one complete up and down cycle in 1 second.
What is a radio band?
A contiguous range of frequencies.
In the 2.4Ghz band, how far apart are the channels?
5MHz
Define signal bandwidth.
It is the width of the frequency space required within the band.
Law of Zero
A value of 0dB means that the two absolute power values are equal.
Law of 3s
A value of 3dB means that the power value of interest is double the reference value.
Law of 10s
A value of 10dB means that the power value of interest is 10 times the reference value.
What is an isotropic antenna?
It is a reference antenna that doesn’t exist. It is a tiny point that radiate RF equally in all directions.
What does EIRP stand for?
Effective Isotropic Radiated Power
What is the calculation for EIRP?
Tx Power (dBm) - Tx Cable Loss (dB) + Tx Antenna Gain (dBi)
What is the difference between EIRP and ERP?
ERP uses the dBd for the antenna gain rather than dBi. dBd is 2.15dBi.
What does RSSI stand for and what is its measurement?
Recieved Signal Strength Indicator (measured in dBm)
What does SNR stand for and how is it calculated?
Signal to Noise Ratio (RSSI - noise floor)
What is the recommended SNR for data and voice?
20+dB for data and 25+dB for voice.
What does FHSS stand for and what is the channel width?
Frequency-Hopping Spread Spectrum (1MHz)
What does DSSS stand for and what is the channel width?
Direct-Sequence Spread Spectrum (22MHz)
What does OFDM stand for and what is the channel width?
Orthogonal Frequency-Division Multiplexing (20MHz)
How many channels in the 2.4GHz range and how many can be used in the US? How many in Europe?
There are 14. 11 used in US. 13 used in Europe.
What is the Barker 11 code?
11 bit sequence that represents 1 bit.
In the Barker code what is a chip and what is a symbol?
Chip is a bit in the sequence. Symbol is a complete group of chips that represent a data bit.
What is CCK stand for and what is it?
Complementary Code Keying (encoding method that takes either 4 or 8 data bits at a time to create a 6-bit symbol)
What does DBPSK stand for and what speed can be achieved?
Differential Binary Phase Shift Keying (1Mb)
What does DQPSK stand for and what speeds can be acheived?
Differential Quadrature Phase Shift Keying - 2Mb using Barker 11, 5.5Mb using CCK 4, 11Mb using CCK 8
How many subcarriers does OFDM use?
64 total
12 guard - help to set channels apart
4 pilot - equally spaced to help evaluate noise
48 data
What is phase?
A measure of shift in time relative to the start of a cycle.
What 2 aspects of the RF signal does QAM alter?
Amplitude and phase.
What does QAM stand for?
Quadrature Amplitude Modulation
