A common early electronics job or set has for many years been the building of a little broadcast transmitter with sufficient power to reach the instant area, however no further. these days that will almost definitely mean an FM broadcast band transmitter, however in earlier decades it may likewise have been for the AM broadcast band instead.

The building of a little AM transmitter provides some fascinating issues for an electronic designer. It is extremely simple to make an AM transmitter with a single transistor or tube, however it is rather more difficult to make a good one. The modulation has to be linear across the whole amplitude range, as well as its impact must not pull the frequency of the oscillator as well as cause FM distortion.

It’s a task [Joe Sousa] has tackled, with his one tube AM transmitter in a Campbell’s soup can. His review of the transmitter contains a full description of the issues he faced, as well as exactly how his style overcomes them. His oscillator is a cathode follower, with the tube biased in class A mode to ensure as undistorted a sine wave oscillation as possible. Modulation is provided with the suppressor grid of the pentode tube he’s using.

The completed transmitter is mounted inside the iconic soup can, with the mains transformer mounted on a removable bottom plate. There is a arrangement for both loop as well as cable antennas to be connected.

It is probable that this transmitter falls under the so-called “Part 15” rules for unlicenced low-power broadcasting in the USA, nevertheless it should be borne in mind that not every area has this provision. If you develop this transmitter, make sure you’re not going to draw in the rate of interest of your regional equivalent of the FCC.

This article should have whetted your appetite for small broadcast transmitters. exactly how about comparing the one right here with a full-sized model?

Thanks [2ftg] for the tip.