ATV Transmitter

Build one on a PCB using only a few componentsI

by Angel Vilaseca HB9SLV and Jean-Pierre Morel HB9RKR

The availability of cheap surplus GaA^-FETs lateh has made a lot of microwave experimenting possible for amateurs. This article describes a new kind of amateur 10 GHz low-power transmitter usins! a surplus GaAsFET, mounted on a tiny piece of Teflon/glass PCB. Wideband FM modulation is possible for ATV operation.

As micro wave-oriented am incurs, we (the authors) began experimenting back in the using Gunn diodes in waveguide assemblies, These, provided they were home-built, using cheap surplus diodes. were \ery cost-effective when compared with commercial transceivers (e.g. the Gunnplexer), [Tie main disadvantage was the "plumbing/' It took a lot of lime and a fairly well-tooted workbench to build waveeuide-based de-

Ftgur? I. A GaAsFETillator G. D. und S — gate, drain, und source respectively.

Figure fn a Yfftff antenna, the elements are about a half-wave length long.

signs. For instance, some part^T tike the screws used to hold the diodes, could onh be made with a lathe.

However, it you were evL-i drawn away from the It) GHz band by the mechanical difficulties, this article is for \ou. The 10 GHz transmitter ^e are describing could hardl) be simpler.

The GaAsFET Oscillator

Tr\in^ to design a GaAsFET oscillator with PUFF, a computer program previously described in this magazine, we first considered a design like the one in Figure 1,

Like in many oscillators, the oscillation takes place if there is an adequate feedback from an amplifier's ouipui to iis input- In the oscillator shown in Figure I. the feedback is provided by the two close-coupled stubs connected to the gate a [id drain microstriplines, 1 he source terminals arc con-nee led to the ground plane.

Making the Oscillator Radiate

Any conducting patch etched on a PCB radiates a pari of the energy ii is fed with. If the dimensions of the patch are small in terms of wavelength, little energy is radiaitrd. As the patch dimensions increase, radiation increases too, until a )J2 patch dimension is

Continued on page IS

Figure 3, The oscillator circuit dimensions, {Sec text.)

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