Chapter 1B: Transmitter & Receiver Flashcards
why is modulation needed?
speech, data signals are low in frequency
to transmit low freq signals using radio waves needs extremely long antenna
what is modulation?
shifting frequency components from a low band to higher frequency band
what is used in frequency shifting for modulation?
high frequency sinewave (carrier)
what is modified in the modulator?
amplitude, frequency, phase
what does a power amplifier do?
increase low output power by modulator
what is a filter?
frequency-selective circuit
difference between ideal & practical filters
ideal: sharp transition from passband to stopband
practical: gradual transition from passband to stopband
what does the bandwidth of BPF = to?
width of passband = fU - fL
fU - upper cutoff freq
fL - lower cutoff freq
at which frequency is voltage gain the maximum of a BPF?
centre frequency
functions of radio receivers
1) pick up radio wave
2) tuning
3) demodulation
4) amplify demodulated signal
what is demodulation?
extracting original information-bearing signal from carrier wave
2 problems with Tuned Radio Frequency
1) bandwidth of BPF is not constant, increases with centre frequency
2) demodulator has to operate at high freq
how to resolve TRF problems?
using superhet receiver
how does superhet receiver resolve the problems of TRF?
1st problem: making intermediate freq constant so bandwidth of BPF will also be constant (ganged tuning maintains IF constant)
2nd problem: high freq needed for demodulator (solved by using mixer)
what happens in amplitude modulation
amplitude/height of carrier wave is changed
frequency does not change
