FM Transmitter and Receiver for a Uni project

In Semester 1 this year I worked on a project to design, simulate and build an FM transmitter and receiver for one of my courses. Together with my project partner Chang, we designed power efficient systems, even if the Receiver had a very high part count.

My Transmitter uses the parasitic capacitance of the NPN transistor to modulate the signal, removing the need for a Varactor. This does however have a drawback; The Q factor is enormously high, to the point where the receiver must have a very precise local oscillator in order to detect the narrow signal. One possible modification I would have liked to make, if I had the time, was to design a proper antenna, rather than using a piece of wire.

The Receiver, which was primarily worked on by my partner until week 8, features a number of filter stages which resulted in a clear output in the simulation. The LO is dereferenced via a simple matching transformer which removes the need for a mirror stage, simplifying the mixer. The PCB layout I designed could still be made more optimal, but is actually quite well routed as is. The only glaring error is the extremely long power trace through the centre, which is offset by a decoupling capacitor at the other end. The design itself also features RF chokes to prevent polluting the voltage source with additional noise.

Both layouts are available below, as well as photographs where available. The photograph of the finished receiver board shows a number of last minute modifications, including moving the antenna and bypassing the BPF stage.

Transmitter layout

Transmitter layout

Receiver layout with annotations for each stage.

Receiver layout with annotations for each stage.

The milled Receiver (L) and Transmitter (R) boards. The drill tolerances are not fantastic, as the machine had not been calibrated in some time.

The soldered Receiver board, some components have been cut out to bypass the faulty BPF stage.

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