This ATU is designed to match our Limerick Sudden transmitter kit. It is a version of the SPRAT circuit by G3WQW that has been copied many times and formed the basis for several kits by others. It uses one coil - a large toroid, and two polyvaricon variable capacitors. It has a simple reflected power indicator which shows when the reflected power is at a minimum.
It will match balanced and unbalanced loads without the use of a balun, it can provide some band-pass filtering for the receiver, and harmonic attenuation for the transmitter. The fixed, although tapped, inductor simplifies construction - no band switches are needed. This kit is only suitable for QRP power levels. The kit uses the “Limerick” method of construction, as used in both the earlier receiver and transmitter. The pads are actually etched on the board (like surface mount), and the interconnections between them are PCB tracks, hidden under the solder masking. No "through hole" connections are made, although "through hole" components are used. The kit includes all components, the complete case, and knobs, and the finished ATU is approximately 10 x 8.5 x 5cm. All you need to supply is a soldering iron & solder (we prefer tin/lead solder), and a few simple hand tools. The iron should be of a reasonable size, as the case is made by soldering the parts together, and a low power iron may not be "man" enough. The ATU input is designed to match to 50 Ohms and should match almost any antenna connected to it. Balanced terminals for high and low impedance are provided, as is an insulated phono (RCA) socket for unbalanced output. The ATU covers the 80m to 10m bands. It does not cover 160m. The kit comes complete with all parts, the base, front and rear panels and the case.
Sudden ATU and Sudden Transmitter
Download the excellent manual: Here.
To order your kit please contact Graham Firth G3MFJ
Members Price - £40 plus postage - £3.50 (UK), £7.50 (EU), or £9.00 (DX),
and should be ordered from club sales.