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Project Notes

#281 FM/ThreeStageTransmitter

Build an “ugly-style in a can” version of dazaro3’s 3-stage FM transmitter circuit.

Build

Notes

I got such good results with LEAP#280 BreadboardTransmitter that I decided to make something more permanent than a breadboard.

Since I have some Altoids tins collecting dust for just such an occasion, I’m doing this “ugly-style in a can”.

Performance

In the initial circuit I have 33pF C4 in the tank circuit. This produced a transmission frequency of 97.4MHz, which happens to be quite busy in my area. After adding another 33pF C9 in parallel (effectively 66pF), I moved the transmission to a much clearer 79.8MHz.

Output power is very good - easily transmits around my house. The microphone is very sensitive, and the pre-amp is fairly high gain. Loud sounds close to the microphone can be quite distorted/clipped.

Construction

Layout is derived from LEAP#280 BreadboardTransmitter design:

ThreeStageTransmitter_layout

A strip of copper PCB is the positive rail anchoring the circuit:

build_01

Lots of space in the can for battery compartment, switch/LED/microphone attachments and the circuit itself. The case provides the ground plane:

build_02

Breadboard

Schematic

Build

The Real Deal

So after hacking away on dazaro3’s designs I thought I should get a “real” one as a way of saying thanks.

It just turned up, and works great. Happily I see the performance is very similar to the builds I’ve done already. Here are some pictures:

fmtuk-unboxed

fmtuk-front

fmtuk-back

Credits and References

About LEAP#281 RadioFM
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.