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Lecture 11-Heterodyne receiver (Mixer (Used to convert the frequency of…
Lecture 11-Heterodyne receiver
3 extra steps after bandpass filter
Mixer
Local oscillator
Filter
Amplifier
Advantages
Electronic components that work at lower frequencies are cheaper than those that work at higher frequencies and easier to build
Heterodyne systems use a mixer to convert the signals in the reciever chain to lower frequencies
helps to avoid oscillation in the signal due to positive feedback in the amplification stages
Attenuation of signal transport in cables is less at lower frequencies
Mixer
Used to convert the frequency of signals
maths
takes input signal and mixes it (multiplies) with signal from local oscilator
Desired frequency has to be selected out by a filter;the power in it is always significantly less than in the original RF signal-called conversion loss in range 6-10dB
Want to produce lower frequencies for further amplification and signal manipulation
The boxes represent the two possible frequency bans (upper and lower sidebands) each of which would be mixed to the same intermediate frequency
usually one or the other is filtered out (by a filter after the mixer) so that both are not mixed together into the IF bnd. This is important to minimied unwanted out-of-band interfering signals
Lots of Maths at end