simulation of a superheterodyne receiver using pspice - School of ...

solution was the use of transformers between circuits to avoid one circuit
loading down another.
* An observation with the Pspice program is that it tends to cling to or hold on
to values after component values are changed. Looking at voltages and
currents through the circuit sometimes showed impossible results and the only
conclusion was that Pspice was still reading previous values for voltages,
currents and component parts even after alterations had been made in the
circuit.
* The main aim of the project was to design and simulate the complete
superhetrodyne receiver. The results of the project can be summarised as
follows: an AM wave was generated with a carrier frequency of 1MHz and a
modulating frequency of 5kHz (i.e. a 10kHz bandwidth). The carrier had an
amplitude of 732mV. The AM signal was fed to an RF amplifier. The image
frequency, set to 1.91MHz, was greatly attenuated at the RF stage. A signal
was generated at the local oscillator stage and when “mixed” or heterodyned
with the RF signal produced the difference or intermediate frequency, which
had an amplitude of 40mV. This difference frequency at 455kHz was
amplified by two IF stages (most of the sensitivity and selectivity found here).
The signal was amplified to a value of 12.6V. The AM detector now detected
this signal. The detector also detected the modulating frequency at 5kHz. The
audio amplifier amplified the difference frequency up to 79.35mV and the
modulating frequency up to 470mV.
In conclusion, although the overall final design did not work completely I feel
good progress was made throughout the project. All of the separate blocks
worked individually but when implemented into a hierarchical structure
problems arose. The biggest problem as previously stated was with loading
effects. The use of transformers and coupling capacitors (in which the values
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