2024年5月11日发(作者：翟清心)
A Rock-Bending Receiver for 7 MHz
This simple receiver by Randy
Henderson, WI5W, originally published in
Aug 1995 QST,is a direct-conversion type
that converts RF directly to audio. Build-
ing a stable oscillator is often the most
challenging part of a simple receiver. This
one uses a tunable crystal-controlled os-
cillator that is both stable and easy to re-
produce. All of its parts are readily
available from multiple sources and the
fixed-value capacitors and resistors are
common components available from many
electronics parts suppliers.
THE CIRCUIT
This receiver works by mixing two
radio-frequency signals together. One of
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
of the mixer in the vicinity of 14 MHz.
ing range with crystal pulling made rock
Instead, we use the frequency difference
bendingseem just as appropriate!
between the incoming signal and the
L2’s value determines the degree of
receiver’s oscillator—a signal in the
pulling available. Using FT-243-style
audio range if the incoming signal and os-
crystals and larger L2 values, the oscilla-
cillator frequencies are close enough to
tor reliably tunes from the frequency
each other. This signal is filtered in U2,
marked on the holder to about 50 kHz be-
and amplified in U2 and U3. An audio
low that point with larger L2 values. (In
transducer (a speaker or headphones) con-
the author’s receiver a 25-kHz tuning
verts U3’s electrical output to audio.
range was achieved.) The oscillator’s fre-
How the Rock Bender Bends
quency stability is very good.
Rocks
Inductor L2 and the crystal, Y1, have
more effect on the oscillator than any other
The oscillator is a tunable crystal oscil-
components. Breaking up L2 into two or
lator—a variable crystal oscillator, or
three series-connected components often
VXO. Moving the oscillation frequency of
works better than using one RF choke.
a crystal like this is often called pulling.
(The author used three molded RF chokes
Because crystals consist of precisely sized
in series—two 10-µH chokes and one
pieces of quartz, crystals have long been
2.7-µH unit.) Making L2’s value too large
calledrocksin ham slang—and receivers,
makes the oscillator stop.
transmitters and transceivers that can’t be
The author tested several crystals at Y1.
tuned around due to crystal frequency
Those in FT-243 and HC-6-style holders
control have been said to be rockbound.
seemed more than happy to react to adjust-
Widening this rockbound receiver’s tun-
ment of C7 (TUNING). Crystals in the
Receivers and Transmitters14.61
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-
µ
F capacitors are monolithic or disc ceramics rated
at 16 V or higher.
C1, C2—Ceramic or mica, 10%
L1—4 turns of AWG #18 wire on
3
/
4
-inch
L3—1-mH RF choke. As a substitute,
tolerance.
PVC pipe form. Actual pipe OD is 0.85
wind 34 turns of #30 enameled wire
C4, C5, and C6—Polystyrene, dipped
inch. The coil’s length is about
around an FT-37-72 ferrite core.
silver mica, or C0G (formerly NP0)
0.65 inch; adjust turns spacing for
Q1—2N2222, PN2222 or similar small-
ceramic, 10% tolerance.
maximum signal strength. Tack the
signal, silicon NPN transistor.
C7—Dual-gang polyethylene-film
turns in place with cyanoacrylic
R10—5 or 10-k
Ω
audio-taper control
variable (266 pF per section) available
adhesive, coil dope or Duco cement.
(RadioShack No. 271-215 or 271-1721
as #24TR218 from Mouser Electronics
(As a substitute, wind 8 turns of #18
suitable).
(800-346-6873, 817-483-4422). Screws
wire around 75% of the circumference
U1—Mini-Circuits SBL-1 mixer.
for mounting C7 are Mouser
of a T-50-2 powdered-iron core. Once
Y1—7-MHz fundamental-mode quartz
#48SS003. A rubber equipment foot
you’ve soldered the coil in place and
crystal. Ocean State Electronics
serves as a knob. (Any variable
have the receiver working, expand
carries 7030, 7035, 7040, 7045, 7110
capacitor with a maximum
and compress the coil’s turns to peak
and 7125-kHz units.
capacitance of 350 to 600 pF can be
incoming signals, and then cement
PC boards for this project are available
substituted; the wider the capacitance
the winding in place.)
from FAR Circuits.
range, the better.)
L2—Approximately 22.7
µ
H; consists of
C12, C13, C14—10% tolerance. For SSB,
one or more encapsulated RF chokes
change C12, C13 and C14 to 0.001
µ
F.
in series (two 10-
µ
H chokes [Mouser
U2—TL072CN or TL082CN dual JFET op
#43HH105 suitable] and one 2.7-
µ
H
amp.
choke [Mouser #43HH276 suitable]
used by author). See text
14.62Chapter 14
2024年5月11日发(作者：翟清心)
A Rock-Bending Receiver for 7 MHz
This simple receiver by Randy
Henderson, WI5W, originally published in
Aug 1995 QST,is a direct-conversion type
that converts RF directly to audio. Build-
ing a stable oscillator is often the most
challenging part of a simple receiver. This
one uses a tunable crystal-controlled os-
cillator that is both stable and easy to re-
produce. All of its parts are readily
available from multiple sources and the
fixed-value capacitors and resistors are
common components available from many
electronics parts suppliers.
THE CIRCUIT
This receiver works by mixing two
radio-frequency signals together. One of
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
of the mixer in the vicinity of 14 MHz.
ing range with crystal pulling made rock
Instead, we use the frequency difference
bendingseem just as appropriate!
between the incoming signal and the
L2’s value determines the degree of
receiver’s oscillator—a signal in the
pulling available. Using FT-243-style
audio range if the incoming signal and os-
crystals and larger L2 values, the oscilla-
cillator frequencies are close enough to
tor reliably tunes from the frequency
each other. This signal is filtered in U2,
marked on the holder to about 50 kHz be-
and amplified in U2 and U3. An audio
low that point with larger L2 values. (In
transducer (a speaker or headphones) con-
the author’s receiver a 25-kHz tuning
verts U3’s electrical output to audio.
range was achieved.) The oscillator’s fre-
How the Rock Bender Bends
quency stability is very good.
Rocks
Inductor L2 and the crystal, Y1, have
more effect on the oscillator than any other
The oscillator is a tunable crystal oscil-
components. Breaking up L2 into two or
lator—a variable crystal oscillator, or
three series-connected components often
VXO. Moving the oscillation frequency of
works better than using one RF choke.
a crystal like this is often called pulling.
(The author used three molded RF chokes
Because crystals consist of precisely sized
in series—two 10-µH chokes and one
pieces of quartz, crystals have long been
2.7-µH unit.) Making L2’s value too large
calledrocksin ham slang—and receivers,
makes the oscillator stop.
transmitters and transceivers that can’t be
The author tested several crystals at Y1.
tuned around due to crystal frequency
Those in FT-243 and HC-6-style holders
control have been said to be rockbound.
seemed more than happy to react to adjust-
Widening this rockbound receiver’s tun-
ment of C7 (TUNING). Crystals in the
Receivers and Transmitters14.61
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-
µ
F capacitors are monolithic or disc ceramics rated
at 16 V or higher.
C1, C2—Ceramic or mica, 10%
L1—4 turns of AWG #18 wire on
3
/
4
-inch
L3—1-mH RF choke. As a substitute,
tolerance.
PVC pipe form. Actual pipe OD is 0.85
wind 34 turns of #30 enameled wire
C4, C5, and C6—Polystyrene, dipped
inch. The coil’s length is about
around an FT-37-72 ferrite core.
silver mica, or C0G (formerly NP0)
0.65 inch; adjust turns spacing for
Q1—2N2222, PN2222 or similar small-
ceramic, 10% tolerance.
maximum signal strength. Tack the
signal, silicon NPN transistor.
C7—Dual-gang polyethylene-film
turns in place with cyanoacrylic
R10—5 or 10-k
Ω
audio-taper control
variable (266 pF per section) available
adhesive, coil dope or Duco cement.
(RadioShack No. 271-215 or 271-1721
as #24TR218 from Mouser Electronics
(As a substitute, wind 8 turns of #18
suitable).
(800-346-6873, 817-483-4422). Screws
wire around 75% of the circumference
U1—Mini-Circuits SBL-1 mixer.
for mounting C7 are Mouser
of a T-50-2 powdered-iron core. Once
Y1—7-MHz fundamental-mode quartz
#48SS003. A rubber equipment foot
you’ve soldered the coil in place and
crystal. Ocean State Electronics
serves as a knob. (Any variable
have the receiver working, expand
carries 7030, 7035, 7040, 7045, 7110
capacitor with a maximum
and compress the coil’s turns to peak
and 7125-kHz units.
capacitance of 350 to 600 pF can be
incoming signals, and then cement
PC boards for this project are available
substituted; the wider the capacitance
the winding in place.)
from FAR Circuits.
range, the better.)
L2—Approximately 22.7
µ
H; consists of
C12, C13, C14—10% tolerance. For SSB,
one or more encapsulated RF chokes
change C12, C13 and C14 to 0.001
µ
F.
in series (two 10-
µ
H chokes [Mouser
U2—TL072CN or TL082CN dual JFET op
#43HH105 suitable] and one 2.7-
µ
H
amp.
choke [Mouser #43HH276 suitable]
used by author). See text
14.62Chapter 14