Circle On Reader Service Card

Photo B. Rock Bender au naturel. The board is mounted on a clear piece of Plexiglas™. The PL-259 antenna connector is wired to the board via RG-i 58 miniature coax. A key jack is at lower left.

by Randy Henderson WI5W

Win QSOs and influence crystals.

by Randy Henderson WI5W

If you want a simple way to generate stable signals, a crystal oscillator will do nicely. The only problem is, yon have one available frequency per crystal. This transmitter will ''bentT' the frequency of your 4"rock" (quartz crystal) to create a tunable oscillator.

The *4Rock Bender" features two stages, an oscillator and a power amplifier. The tuning range varies with individual crystals. Various; 7 MHz crystals will allow 6 to 20 kHz of tuning range. The version shown here has an output power of 3 watts into a 50 ohm load, A slight modification allows output levels of 10 watts or greater. It is extremely tol e rant o f m i sm ate hed I oads.

Construction

The circuir board is double-sided. One side is a conventional etched pattern, shown in Figure 1. The other side is a solid copper ground plane, except where holes are drilled for component leads. All ground connections are soidered on this side. If you are making your board from the pattern, many methods can be used to form the resist paths. These include: tape, resist pen, and photo resist. See the construction chapter in recent versions of th&ARRL Handbook to learn more about such techniques. Enamel spray paint is an easy way to cover the ground plane.

All components mount on the ground plane side (sec Photo B). Only grounded leads are soldered to the ground plane. Ail other leads pass through the ground plane to the etched side of the board. They must not make contact with the ground plane. To prevent accidental contact, countersink the ground plane at the holes indicated as ungrounded in Figure 2. Use a substantially larger bit for countersinking than the component lead hole 0/4" to 1/2"). Light pressure on the drill will clear away copper from the periphery of the holes (see Photo C).

Place the components as shown in Figure 2h Q2, the TRF511 output transistor, should be mounted close to the board with short leads, as well as C8.1 leave conductive foam, aluminum foil, or wire, on the leads of Q2 until all of the board components are soldered in place- Shorting the leads together protects against damage from static electric charges and soldering iron leakage. Don't forget to remove the short before applying power. All other components should have reasonably short leads. Q2, L4 and the cry stal socket will need larger holes and countersunk areas.

The variable capacitor C2 docs not solder directly to the board. Use a short, stiff wire jumper to connect the stator plates (see Photo D). Most defunct AM broadcast receivers have small polyethylene film variable capacitors suitable tor C2. To my knowledge, all use metric-sized screws. Many have internally threaded shaft ends. 111 nd that some rubber cabinet feet make suitable knobs when the original is not available. Use care when mounting variable capacitors. Do not run the screws in far enough to damage the plates. Use washers„ spacers or shorter screws. If necessary, shorten the screw and repair the threaded end.

L4 is made of 22-t & AWG solid copper wire. Enamel insulation is preferable, but not essential. Wind four turns over a 3/4* inch-long PVC pipe section, The size of pipe used for the coil form is known as '11/2-inch,'1 This is a convention used by the plumbing industry and is not the actual outside diameter, The outside diameter is approximately 0.84 inches. The length of the winding is about 1/2 inch- Do not secure or cement the turns in place at this stage of construction.

The mounting holes for the circuit board are not shown in the layout. Place mounting holes as you wish, but do not allow supports to short or ground conductors on the etched side of the board.

Although Figure 3 doesn't show a fuse, some type of

Photo A. This well-dressed Rock Bender sports a black-and-gray cabinet from Mouse r Electronics (part number 4GUB10 J). The key, jack is near the lower left corner of the front panel. The tuning knob is a black rubber cabinet fool.

Photo B. Rock Bender au naturel. The board is mounted on a clear piece of Plexiglas™. The PL-259 antenna connector is wired to the board via RG-i 58 miniature coax. A key jack is at lower left.

Photo C. Countersunk holes on the ground plane provide safe passage for component leads without disturbing printed circuit paths on the other side.

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