Advanced Topics Flashcards
Living tissue
is a complex arrangement of primarily lossy dielectrics, often modelled as a saline solution
RF radiation range
3 kHz- 300 GHz, non-ionizing and not conclusively tied to chronic health effects
Nerve stimulation
below 10 MHz, tingling, discomfort, pain
Tissue heating
several adverse effects for body temperature rising 1 degree C or more
Health Canada’s Safety Code 6
defines limits to prevent adverse health effects from RF radiation
RSS-102
The ISED adoptions of Health Code 6 for radio communication apparatus
ISED
Innovation, Science and Economic Development Canada
Basic restrictions
SAR (W/kg), APD (W/m^2), internal E-field (Vrms/m)
ISED TN-261
reflected amplitude ~60% of the direct path
Radiopropagation
attenuation on the order of 100dB, multipath leads to rapid fluctuations of 10’s of dB over time and space, relative motion of Tx and Rx or in the environments leads to Doppler shifts
Components of the Superheterodyne Receiver
Rx Antenna
RF Amplifier
Mixer
Local Oscillator
Bandpass Filter
IF Amplifier (gain control)
Phase Lock Loop (frequency control)
LO is tuned to
maintain a fixed intermediate frequency (IF)
IF amp is tuned to
maintain a fixed IF output power
Radio performance is limited by
noise
Thermal noise
The most fundamental types of noise, all particles above absolute zero undergo thermal vibrations. Charges vibrating in a resistive medium produce random noise voltages.
At RF thermal noise is
spectrally white, zero-mean and Gaussian distributed (AWGN)
Radio receiver noise sources
shot noise, flicker noise
Shot noise
tends to be similar to thermal noise so we add them (AWGN)
Flicker noise
has 1/f characteristic, which we avoid by choosing a suitable IF
Minimum acceptable SNR
10 dB
Noise Figure
quantifies the reduction in SNR from input to output of a noisy device
Noise figure assumes
matched on all ports and input noise temperature is To = 290K. Often quoted in dB
Terrestrial Radio Propagation modes
Sky waves
Ground waves
Line of sight waves
Sky wave significant frequency
3MHz and down
Ground wave significant frequency
30MHz and down
LOS wave significant frequency
VHF (30-300MHz) and up
What increases the limit of LOS
radio signals bend back due to refraction
