Radio Shack RS-2000 Manual de usuario descargar pdf (Pagina 3)

September 2000 63

frequency range of the receiver. You can compensate for this by

removing turns from L1 if necessary.

Two-Band Option

If you’d like a two-band receiver with noncritical tuning, use

a 150-pF capacitor for C1 and install a miniature toggle switch

with very short leads to add an additional 250-pF fixed-value mica

capacitor in parallel with C1. With the capacitor in the circuit, the

receiver will then tune the 80-meter band.

Packaging the Radio

The recommended RadioShack project box includes metal and

plastic tops. Use the metal top as a large front panel by mounting

it to one side of the box using two small screws and nuts through

two of the four predrilled holes. Then drill the control mounting

holes and mount the three controls and the ON/OFF switch on the

metal panel. The radio is easier to operate if you mount the TUN-

ING

capacitor and the regeneration (REGEN) control on opposite

sides of the front panel. The VOLUME and REGEN controls are best

mounted near the bottom of the front panel to keep their connect-

ing wires to the PC board as short as possible. You can use the

RadioShack hook-up wire for the

VOLUME and REGEN control

connections if you twist the wires closely together and keep their

lengths very short. Otherwise, use shielded wires for these con-

nections. You can mount the ON/OFF switch last, in any conve-

nient location. Use one of the two remaining holes in the metal

front panel to attach a wire connecting the panel to the PC board

ground. Attach the PC board and the coil to the bottom of the

project box using small screws. Mount the headphone jack on the

box rear, close to the PC board and the LM386. Attach the

RadioShack 39-inch whip antenna to one of the back corners of the

box using a small screw and nut.

If you use the RadioShack jack specified for J1 (RS 274-276),

connect together pins 2 and 5 and attach that common lead to C8.

Ground pin 1 of the jack. If you intend to use a small speaker,

connect it between pins 1 and 3. Then, when headphones are

plugged in, the speaker will be disconnected automatically.

Testing and Operating the Receiver

Set the VOLUME and REGEN controls to midrange, plug in the

headphones, extend the whip antenna, attach the battery and turn

on the receiver. You can check to ensure that the audio stage is

functioning by placing a finger on the center lug (wiper) of the

VOLUME control and listen for a buzz. If the audio stage is work-

ing, adjust the REGEN control until the set produces a sound, in-

dicating that Q1 is oscillating. If Q1 is not oscillating, carefully

check the wiring and measure the voltages labeled on the sche-

matic using a high-impedance DVM or multimeter. Common prob-

lems are Q1 being wired backwards (emitter and collector connec-

tions reversed) and the wires from coil L1 connected to the wrong

places on the PC board.

Use two hands when operating the receiver: one for tuning, the

other for controlling regeneration. For international broadcast

stations or AM phone operation on 40 meters, carefully adjust the

REGEN control so that Q1 is just below oscillation. For CW and

SSB, increase the REGEN level so that the set just oscillates pro-

viding the required local oscillation for these modes. This receiver

picks up lots of stations with just its whip antenna, although using

a ground connection will greatly reduce any hand-capacitance ef-

fects. To pull in more stations during daylight hours, a 10 to 15-

foot (or longer) length of insulated hook-up wire can be used as an

external antenna. Simply wrap the end of this wire a couple of

times around the whip antenna.

If you operate this receiver close to another radio, the regen’s

30-µW oscillator might interfere with it. Those who are interested

This close-up shows the interconnection of series-

connected D1, C4 and R4 between the

TUNING

capacitor

and

VOLUME

control.

drill a mounting hole in the bottom of the film can or pill bottle.

Then, drill two small holes in the side of the coil form, near the top,

where the winding starts. (By winding from the top of the coil

form to the bottom, the winding bottom is kept well above the PC

board, preventing any circuit loading that could decrease the

receiver’s selectivity.) Feed one end of the coil wire through the

first hole to the inside of the form, then out through the second. Tie

a knot at the point in the wire where it enters the form—this keeps

the wire in place and prevents it from loosening later on. Be sure

to leave a two to three inch length of wire at each end of the coil

so you can make connections to the PC board.

You can wind the coil in either direction, clockwise or counter-

clockwise. Tightly wind the wire onto the form, counting the turns

as you go. Keep the turns close together and don’t let the wire

loosen as you wind; this takes a little practice.

To make the coil tap, wind 11 turns on the coil form. While

holding the wire with your thumb and index finger, mark the tap

point and remove the insulation at that point. Solder a two to three-

inch piece of wire to the tap. Continue winding turns until the coil

is finished (13 turns total). Keep the free end of the wire in place

using a piece of tape and drill two more holes in the coil form

where the winding ends. Feed the wire end in and out of the coil

as before and tie a knot at the end to hold the winding in place.

When the coil is finished, remove the tape then carefully solder the

three wires from the coil (bottom, tap and top) to their points on

the PC board keeping the wire lengths as short as possible.

For best performance, the floating detector must be wired using

short, direct connections. Therefore, these components are not

mounted on the PC board. Mount the

VOLUME

control, R5, close to

the

TUNING

capacitor, C1. Connect D1, C4 and R4 in series be-

tween the hot side of C1 (the stator) and the top of the

VOLUME

control.

Options

Fine-Tuning Control

You can add a fine-tuning control to the receiver using the

circuit shown in the inset of Figure 1. D6 functions as a poor man’s

Varactor (voltage-variable capacitor). As the voltage from FINE-

TUNING control R8 is increased, the diode is reverse biased and its

capacitance decreases. This fine-tuning control is cheap and easy

to add, but its added capacitance somewhat reduces the maximum

1 2 3 4

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