GaAs FET preamp

Posted on Feb 5, 2014

To build a GaAs FET preamp that has good gain and extremely low noise from readily available components. This preamp is stable with differing source and load situations. The circuit is built dead bug style on a piece of printed circuit board for a good ground plane. The FET sits on a stand made from a piece of copper or brass shim stock or strap

GaAs FET preamp
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" x 1- " bent into shape. This stand is used to support the source capacitors and the FET. Leadless disc`s or chip capacitors are used for the source capacitors, and output capacitor. Use generally accepted practices for vhf and uhf work. The power and RF section of the preamp must be kept separated. The use of a shield (screen) or separate compartment for the PS is suggested. The power supply section can be built on the under side of the preamp if double sided pc board is used, however this practice is not recommended if board is placed on the lid of a "Bud Box" which is common construction of this style preamp. The transistor stand is bent at these intervals, ", 1/8", ½", 1/8" to produce a _-_ (a little tough to produce with text, but you get the idea) The parts that have values listed on the schematic do not change from band to band. Q1 is a Mitsubishi GaAs Fet from the MGF 1200, 1300, or 1400 family. My favorite is the MGF-1402. The completed unit should be placed into a shielded enclosure, especially if it is going to be placed at a repeater site. Alternately, the circuit can be placed into the receiver cabinet itself. Noise Figure tests were made by professional equipment to determine NF. A HP 8970 A and 346A were used for the tests. When constructed properly the units will be less than. 5 dB with. 40 to. 45 being typical. Gain is about 24 dB on 2 meters somewhat less on 220 and 440. The circuit is extremely stable...

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