Heterodyne means to mix two frequencies together in a nonlinear device (such as
transistor, diode mixer e.t.c.) or to transmit one frequency to another using nonlinear
mixing. Mixing two frequencies creates two new frequencies, one at the sum of the two
frequencies mixed and the other at their difference.
Heterodyne receiver is a telecommunication receiver which uses this effect to produce
frequency shifts. The receiver also known as frequency conversion, the high frequency is
down converted to low frequency (IF) and the main amplification takes place at IF stage.
A super heterodyne receiver converts all incoming radio frequency (RF) signals to a
lower frequency known as an intermediate frequency (IF). Super-heterodyne receivers
have superior characteristics to simpler receiver types in frequency stability and
selectivity. The shortcomings of the TRF receiver are overcome by the super heterodyne
receiver. These drawbacks overcomed are;
- Stability – as high frequency is down converted to IF the reactance of stray
capacitances will not decrease as it was at higher frequencies resulting in increased
feedback.
- No variation in BW- as IF range is 438 to 465 KHz (in case of AM receivers) mostly
455 KHz, appropriate for Q limit (120).
- Better selectivity- as no adjacent channels are picked due to variation in BW.
transistor, diode mixer e.t.c.) or to transmit one frequency to another using nonlinear
mixing. Mixing two frequencies creates two new frequencies, one at the sum of the two
frequencies mixed and the other at their difference.
Heterodyne receiver is a telecommunication receiver which uses this effect to produce
frequency shifts. The receiver also known as frequency conversion, the high frequency is
down converted to low frequency (IF) and the main amplification takes place at IF stage.
A super heterodyne receiver converts all incoming radio frequency (RF) signals to a
lower frequency known as an intermediate frequency (IF). Super-heterodyne receivers
have superior characteristics to simpler receiver types in frequency stability and
selectivity. The shortcomings of the TRF receiver are overcome by the super heterodyne
receiver. These drawbacks overcomed are;
- Stability – as high frequency is down converted to IF the reactance of stray
capacitances will not decrease as it was at higher frequencies resulting in increased
feedback.
- No variation in BW- as IF range is 438 to 465 KHz (in case of AM receivers) mostly
455 KHz, appropriate for Q limit (120).
- Better selectivity- as no adjacent channels are picked due to variation in BW.
