them is the signal you want to hear, and the other is generated by an oscillator circuit (Q1 and associated components) in the receiver. In Fig 14.61, mixer U1 puts out sums and differences of these signals and their harmonics. We don’t use the sum of the original frequencies, which comes out Because crystals consist of precisely sized
pieces of quartz, crystals have long been
called rocks in ham slang—and receivers,
transmitters and transceivers that can’t be
tuned around due to crystal frequency
control have been said to be rockbound.
Widening this rockbound receiver’s tun-
in series—two 10-µH chokes and one
2.7-µH unit.) Making L2’s value too large
makes the oscillator stop.
The author tested several crystals at Y1.
Those in FT-243 and HC-6-style holders
seemed more than happy to react to adjust-
ment of C7 (TUNING). Crystals in the
Receivers and Transmitters
14.61
smaller HC-18 metal holders need more inductance at L2 to obtain the same tuning range. One tiny HC-45 unit from Interna-tional Crystals needed 59 µH to eke out a mere 15 kHz of tuning range.
Input Filter and Mixer
C1, L1, and C2 form the receiver’s in-put filter. They act as a peaked low-pass network to keep the mixer, U1, from re-
sponding to signals higher in frequency
than the 40-meter band. (This is a good
idea because it keeps us from hearing
video buzz from local television transmit-
ters, and signals that might mix with har-
monics of the receiver’s VXO.) U1, a
Mini-Circuits SBL-1, is a passive diode-
ring mixer. Diode-ring mixers usually per-
form better if the output is terminated
properly. R11 and C8 provide a resistive
termination at RF without disturbing
U2A’s gain or noise figure.
Audio Amplifier and Filter
U2A amplifies the audio signal from
U1. U2B serves as an active low-pass fil-
ter. The values of C12, C13 and C14 are
Fig 14.61—An SBL-1 mixer (U1, which contains two small RF transformers and a Schottky-diode quad)
, a TL072 dual op-amp IC (U2) and an LM386 low-voltage audio power amplifier IC (U3) do much of the Rock-Bending Receiver’s magic. Q1, a variable crystal oscillator (VXO), generates a low-power radio signal that shifts incoming signals down to the audio range for amplification in U2 and U3. All of the circuit’s resistors are 1/4-W, 5%-tolerance types; the circuit’s polarized capacitors are
16-V electrolytics, except C10, which can be rated as low as 10 V. The 0.1-µF capacitors are monolithic or disc ceramics rated at 16 V or higher.
C1, C2—Ceramic or mica, 10% tolerance.
C4, C5, and C6—Polystyrene, dipped silver mica, or C0G (formerly NP0) ceramic, 10% tolerance.
C7—Dual-gang polyethylene-film variable (266 pF per section) available as #24TR218 from Mouser Electronics (800-346-6873, 817-483-4422). Screws for mounting C7 are Mouser
#48SS003. A rubber equipment foot serves as a knob. (Any variable capacitor with a maximum capacitance of 350 to 600 pF can be substituted; the wider the capacitance range, the better.)
C12, C13, C14—10% tolerance. For SSB, change C12, C13 and C14 to 0.001 µF. U2—TL072CN or TL082CN dual JFET op amp.L1—4 turns of AWG #18 wire on 3/4-inch PVC pipe form. Actual pipe OD
is 0.85 inch. The coil’s length is about
0.65 inch; adjust turns spacing for maximum signal strength. Tack the turns in place with cyanoacrylic adhesive, coil dope or Duco cement. (As a substitute, wind 8 turns of #18 wire around 75% of the circumference of a T-50-2 powdered-iron core. Once you’ve soldered the coil in place and have the receiver working, expand and compress the coil’s turns to peak incoming signals, and then cement the winding in place.)
L2—Approximately 22.7 µH; consists of one or more encapsulated RF chokes in series (two 10-µH chokes [Mouser #43HH105 suitable] and one 2.7-µH choke [Mouser #43HH276 suitable]
used by author). See text L3—1-mH RF choke. As a substitute, wind 34 turns of #30 enameled wire around an FT-37-72 ferrite core.
Q1—2N2222, PN2222 or similar small-signal, silicon NPN transistor.
R10—5 or 10-kΩ audio-taper control (RadioShack No. 271-215 or 271-1721 suitable).
U1—Mini-Circuits SBL-1 mixer.
Y1—7-MHz fundamental-mode quartz crystal. Ocean State Electronics carries 7030, 7035, 7040, 7045, 7110 and 7125-kHz units.
PC boards for this project are available from FAR Circuits.
14.62Chapter 14
appropriate for listening to CW signals. If you want SSB stations to sound better, make the changes shown in the caption for Fig 14.61.
U3, an LM386 audio power amplifier IC, serves as the receiver’s audio output stage. The audio signal
at U3’s output is more than a billion times more powerful than a weak signal at the receiver’s input, so don’t run the speaker/earphone leads near the circuit board. Doing so may cause a squealy audio oscillation at high volume settings.
CONSTRUCTION
If you’re already an accomplished builder, you know that this project can be built using a number of construction tech-niques, so have at it! If you’re new to building, you should consider building the Rock-Bending Receiver on a printed circuit (PC) board. (The parts list tells where you can buy one ready-made.) See Fig 14.62 for details on the physical lay-out of several important components used in the receiver. Fig 14.63 shows photos of two different receivers using two differ-ent approaches to construction—one us-ing a PC board and the other using “ugly”techniques.
If you use a homemade double-sided circuit board based on the PC pattern on the accompanying CD, you’ll notice that it has more holes than it needs to. The extra holes (indicated in the part-placement dia-gram with square pads) allow you to con-nect its ground plane to the ground traces on its foil side. (Doing so reduces the in-ductance of some of the board’s ground paths.) Pass a short length of bare wire (a clipped-off component lead is fine) into each of these holes and solder on both sides. Some of t
he circuit’s components (C1, C2 and others) have grounded leads accessible on both sides of the board. Sol-der these leads on both sides of the board. Another important thing to do if you use a homemade double-sided PC board is to countersink the ground plane to clear all ungrounded holes. (Countersinking clears copper away from the holes so compo-nents won’t short-circuit to the ground plane.) A 1/4-inch-diameter drill bit works well for this. Attach a control knob to the bit’s shank and you can safely use the bit as a manual countersinking tool. If you countersink your board in a drill press, set it to about 300 rpm or less, and use very light pressure on the feed handle. Mounting the receiver in a metal box or cabinet is a good idea. Plastic enclosures can’t shield the TUNING capacitor from the presence of your hand, which may slightly affect the receiver tuning. You don’t have to completely enclose the receiver—a flat aluminum panel screwed to a wooden base
is an acceptable alternative. The panel
supports the tuning capacitor, GAIN con-
trol and your choice of audio connector.
The base can support the circuit board and
antenna connector.
CHECKOUT
Before connecting the receiver to a
power source, thoroughly inspect your
work to spot obvious problems like solder
bridges, incorrectly inserted components
or incorrectly wired connections. Using
the schematic (and PC-board layout if you
built your receiver on a PC board), recheck
every component and connection one at a
time. If you have a digital voltmeter
(DVM), use it to measure the resistance
between ground and everything that
should be grounded. This includes things
like pin 4 of U2 and U3, pins 2, 5, 6 of U1,
and the rotor of C7.
If the grounded connections seem all
right, check some supply-side connections
with the meter. The connection between
pin 6 of U3 and the positive power-supply
lead should show less than 1 Ω of resis-
tance. The resistance between the supply
lead and pin 8 of U1 should be about 47 Ω
because of R1.
If everything seems okay, you can apply
power to the receiver. The receiver will
work with supply voltages as low as 6 V
and as high as 13.5 V, but it’s best to stay
within the 9 to 12-V range. When first test-
ing your receiver, use a current-limited
power supply (set its limiting between 150
and 200 mA) or put a 150-mA fuse in the
connection between the receiver and its
power source. Once you’re sure that every-
thing is working as it should, you can re-
move the fuse or turn off the current
limiting.
If you don’t hear any signals with the
antenna connected, you may have to do
some troubleshooting. Don’t worry; you
can do it with very little equipment.
TROUBLE?
The first clue to look for is noise. With
the GAIN control set to maximum, you
should hear a faint rushing sound in the
speaker or headphones. If not, you can use
a small metallic tool and your body as a
Fig 14.62—The Mouser Electronics part suggested for C7 has terminal
connections as shown here. (You can use any variable capacitor with a maximum capacitance of 350 to 600 pF for C7, but its terminal configuration may differ from that shown here.) Two Q1-case styles are shown because plastic or metal transistors will work equally well for Q1. If you build your Rock-Bending Receiver using a prefab PC board, you should mount the ICs in 8-pin mini-DIP sockets
rather than just soldering the ICs to the board.
Receivers and Transmitters14.63
sort of test-signal generator. (If you have any doubt about the safety of your power supply, power the Rock-Bending Receiver from a battery during this test.) Turn the GAIN  control to maximum. Grasp the me-tallic part of a screwdriver, needle or whatever in your fingers, and use the tool to touch pin 3 of U3. If you hear a loud scratchy popping sound, that stage is working. If not, then something directly related to U3 is the problem.
You can use this technique at U2 (pin 3,then pin 5) and all the way to the antenna.If you hear loud pops when touching ei-ther end of L3 but not the antenna connec-Fig 14.63—Ground-plane construction,PC-board construction—both of these
approaches can produce the same good Rock
Bending Receiver performance. (WI5W built the one that looks nice, and ex-W9VES—who wrote this caption—built the one that doesn’t.)
react to啥意思
tor, the oscillator is probably not working.You can check for oscillator activity by putting the receiver ne
ar a friend’s trans-ceiver (both must be in the same room) and listening for the VXO. Be sure to adjust the TUNING  control through its range when checking the oscillator.
The dc voltage at Q1’s base (measured without the RF probe) should be about half the supply voltage. If Q1’s collector volt-age is about equal to the supply voltage,and Q1’s base voltage is about half that value, Q1 is probably okay. Reducing the value of L2 may be necessary to make some crystals oscillate.
OPERATION
Although the Rock-Bending Receiver uses only a handful of parts and its fea-tures are limited, it performs surprisingly well. Based on tests done with a Hewlett-Packard HP 606A signal generator, the receiver’s minimum discernible signal (by ear) appears to be 0.3 µV. The author could easily copy 1-µV signals with his version of the Rock-Bending Receiver.
Although most HF-active hams use transceivers, there are advantages in using separate receivers and transmitters. This is especially true if you are trying to as-
semble a simple home-built station.

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