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W-J ← WJ-8711
HF surveillance and monitoring receiver
WJ-8711A is a DSP-based HF monitoring receiver for the
5 kHz to 30 MHz frequency range, introduced around 1996 by
Watkins-Johnson (W-J) in Gaithersburg (MD, USA)
as an updated version of the highly successful WJ-8711, which
had been in production from 1991-1996 [2].
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Like its predecessors and other contemporary receivers, the WJ-8711A is housed
in a 19" 3U enclosure, but weights far less, due to the use of miniature (SMD)
components and the simple non-modular mechanical construction. As such it is
probably the lightest receiver in its class.
The front panel is clear and well layed out, and operation is intuitive.
The use of a digital signal processor (DSP) not only simplifies the
design, but also boosts its IF and AF performance.
The audio quality is superb and the bandwidth can be set between
56 Hz and 16 kHz in 66 steps.
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The use of a DSP makes it possible to update the receiver with new
waveforms and improved performance, simply by issueing a firmware update.
It also significantly reduces the production cost. As a unit price of
US$ 20,486, it was less than half the price of competing receivers like the
AEG telefunken E-1800/A.
The WJ-8711A was in production from 1996 to 2010.
The 'black box' version of the receiver (without front panel, but with
V.24 interface) is known as the WJ-8712A.
The WJ-8711A was the last self-contained stand-alone receiver from W-J
before everthing went fully digital. It is similar in appearance and
operation to the contemporary but cheaper Ten-Tec RX-340, which was released
around the time of the introduction of the original WJ-8711 (1990),
but was aimed at the amateur market.
For comparison between the two receivers,
refer to [5].
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Below is the front panel of the WJ-8711A. The controls are grouped
as indicated by grey segments and white lines. At the right is the
frequency tuning section with a large clear green 8-digit readout.
At the bottom right is the tuning knob, of which the tuning step can
be altered from 1 MHz down to 1 Hz. Direct entry of the desired
frequency is possible via the 16-button keypad.
At the centre are the settings for Automatic Gain Control (AGC),
Beat Frequency Oscillator (BFO), noise blanker, IF bandwidth,
waveform (mode) and squelch, all of which can be adjusted with a single
knob. In addition, this section gives access to a menu with various
other parameters.
The section at the left gives access to the device's memory, in which
up to 100 channels can be programmed. Scanning is possible at a speed
of 150 channels per seconds. It is also possible to scan a band segment
by setting the upper and lower boundaries. Along the bottom edge are
controls for adjusting the RF gain and the audio volume (of the
internal or external speaker). A separate volume control is available for
the headphones, to the right of the 6 mm jack socket.
All connections (with exception of the headphones) are at the rear of the
device, shown in the image above. At the right is the connection to the
internal switched-mode power supply unit, which accepts 100-254V AC.
At the bottom left are four BNC sockets for connection of the antenna,
an optional signal monitor, an optional external 10 MHz reference input
and the 455 kHz IF output. At the centre is a black contact strip to
which the external speaker can be connected. There are also two
transformer-isolated line outputs, plus a couple of switching contacts.
For external control from a computer, a simple V.24 port is
available. It supports the CSMA protocol.
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- WJ-8711
This is the initial version of the receiver, released in 1991.
It was developed at the request of a US government agency, presumably
the NSA or the CIA, in an attempt to significantly reduce the price
of surveillance and monitoring receivers.
➤ More
- WJ-8711A
This is an improved version of the WJ-8711, in which the DSP has been
replaced with a different type, and the firmware has been adapted
accordingly. This version also contains a number of
improvements and enhancements (see below).
The device featured here is of this type.
The following differences with the original WJ-8711 have been recorded:
- Different DSP (and firmware)
- Improved performance
- Improved audio quality
- Better suppression of internally generated noise
- WJ-8711A-3
Government version of the WJ-8711A, with the following extras:
- FSK mode
- Preselector fitted
- Internal loudspeaker fitted
- High stability reference oscillator
- HF-1000
Consumer (amateur) version of the WJ-8711, aimed at shortwave listeners
and amateur radio operators.
- HF-1000A
Amateur version of the WJ-8711A.
- WJ-8712
Black box version of the WJ-8711, without control panel. Can only be
controlled via the V.24 interface.
- WJ-8712A
Black box version of the WJ-8711A, without control panel. Can only be
controlled via the V.24 interface.
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Below is the block diagram of the WJ-8711A. The antenna input at the
top left is fed — via an optional preselector — to the input of the
RF subsystem. The 25 kHz output from the RF subsystem is then fed
to a DSP and finally to the IF/AF subsystem, after which the audio
is delivered to the headphones and optionally to an internal or external speaker.
All subsystems are controlled by the central
processing unit (CPU), which is interfaced to the front panel (Controls).
The radio can also be controlled
via the V.24 (RS232/CSMA) interface at the rear of the device.
Below is a more detailed block diagram of the RF subsystem. The signal from
the antenna is first fed (via an optional preselector) to a low-pass filter
and then optionally through a preamplifier or attenuator, before it is passed
to the first mixer (IF1), where it is mixed with the 1st LO. The IF1 output
at 40.455 MHz is then mixed in the second mixer (IF2) with 40 MHz from the
2nd LO, resulting in a 455 kHz signal. In the 3rd mixer (IF3) this
455 kHz signal is mixed with 430 kHz from the 3rd LO to obtain a balanced
25 kHz signal that can be processed by the DSP subsystem.
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RF subsystem - block diagram
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The balanced 25 kHz signal from the IF3 stage is fed to a 16-bit ADC that
samples it at 100 kHz. The resulting digital data is fed to a pre-programmed
DSP that performs a variety of operations and functions, such as 1 Hz fine
tuning IF filtering, RSSI, AGC, BFO, squelch and demodulation.
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DSP/AF subsystem - block diagram
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After processing, the DSP output is converted back to the analogue
domain with a DAC. This is a multiplexed signal that carries both side
bands of an ISB signal. The multiplexed signal is demultiplexed,
resulting in separate LSB and USB components that are passed to the
headphones. The signals are also available as LINE A and LINE B signals.
The multiplexed signal from the output of the DAC is also upconverted
to 455 kHz, filtered, buffered and passed to the IF output
at the rear.
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The interior of the WJ-8711A can be accessed by removing 10 screws
(2 at the top, two at the rear, 3 at the left and 3 at the right),
after which the top panel can be lifted off.
This reveals the interior, as shown in the image above.
The device is surprisingly empty, which explains its low weight.
At the left is the wide range switched-mode power supply, which
accepts 100-254V/AC.
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Inside the enclosure are just three printed circuit boards:
(1) the digital board, (2) the tuner board and (3) the front panel board.
The latter is mounted behind the front panel. Each of the three boards
is discussed in more detail below.
At the center of the device, to the right of the PSU, is the
digital board with the CPU and DSP. It controls all parts of the
radio. It is connected to the tuner board and to the front panel
PCB by means of two 24-wire rainbow ribbon cables.
It has a DB25 socket with the V.24 control port
and a contact strip for audio and switching outputs.
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To the right of the digital board is the slightly larger
tuner board. It holds the analogue RF
circuits, plus the three IF stages, each with their own mixer
and synthesizer, all driven by a common highly stable 10 MHz
reference signal.
The RF and IF circuits are built with SMD parts,
and are spread over a series of shielded
compartments, each covered by a metal cap (that has been removed
in the image on the right).
At the bottom of the board are some larger
parts, such as a wideband amplifier and the 10 MHz
temperature-compensated crystal oscillator (TCXO).
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The tuner board is connected to the digital board via a short
24-pin rainbow ribbon cable. This includes the balanced 25 kHz IF3
signal, which is digitized by means of a 16-bit ADC on the digital
board and then passed to the DSP. All IF/AF processing is done
on the digital board.
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Also connected to the digital board is the front panel assembly, shown
in the image on the right. Is consists of a large PCB that runs over the
full width of the receiver. It holds the displays, rotary encoders
and push-buttons, some of which protrude the aluminium front panel.
The image on the right shows the solder side of the front panel PCB.
The front panel has its own microcontroller (not visible here) of which
the firmware is held in an EPROM at the solder side
(here visible on the far left). This allows it to be swapped without disassembling
the front panel.
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The signal strength indicator is an old type moving coil instrument
which is housed in a separate aluminium enclosure that is fitted to the
front panel PCB. It is backlit with a light bulb and is driven by the
front panel microcontroller, based on the RSSI value provided by the DSP.
Aside the PCB (here visible on the far right) is the
mains power switch wiring and the headphones socket.
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When we received our WJ-8711A in March 2025, it was in working condition,
but had only been cleaned superficially. On the inside, a very fine dust had
settled, and the edges of the PCBs were oxidised, probably as a result of
extended storage in a damp place. In order to clean the PCBs, the entire unit
was taken apart and the individual boards were thoroughly cleaned. At this stage,
we took safety copies of the three EPROMs and inspected the Dallas timekeeping
unit with built-in Lithium battery. As the latter was still OK, it was decided to
place it back for now.
Next, the PSU was inspected. Based on the quality of the electrolytic capacitors
inside the PSU, it was deciced to replace them all with modern alternatives. The
smaller ones were replaced with 125°C low-ESR types, whilst the bigger ones were
replaced by 105°C long-life low-ESR types. As mains filter units tend to break
down after several years, it was also decided to replace the mains filter of the
WJ-8711A — which is integrated with the mains power receptacle — preemptively.
The device was then reassembled and thoroughly tested, to ensure that it works as
expected.
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Extremely dirty PSU capacitors in bad state
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- Exterior and interior thoroughly cleaned
- EPROM contents read and stored
- Mains filter replaced
- Electrolytic capacitors in PSU swapped
- Dallas timekeeper IC inspected
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This is the antenna input, terminated at 50Ω.
Note that the antenna input is not protected against static discharge
and thunder storms by means of a surge arrestor. This can be fixed by
installing the optional preselector, which does have a surge arrestor
at its input.
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ANT Out Antenna input (50Ω) GND - Ground
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Signal monitor output (SMO)
A3J2
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On this connector a 455 kHz IF signal is available with a bandwidth
of 20 kHz (-3dB). The signal is taken directly from the output of the IF2 stage.
It is buffered and can be used for connecting an external spectrum monitor
(panorama viewer). Note that it will only show 20 kHz of the spectrum.
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SMO Out Signal Monitor Output GND - Ground
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By default, all internal frequencies are derived from a highly stable
internal temperature-compensated 10 MHz reference oscillator. If necessary,
the device can be locked to an external 1, 2, 5 or 10 MHz source, that can be
connected to the EXT REF socket (A3J3) at the rear. When a valid signal is
detected on this port, the WJ-8711A will automatically the external signal.
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EXT/REF In External 1, 2, 5 or 10 MHz reference GND - Ground
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On this socket, the 455 kHz Intermediate Frequency (IF) signal is available.
This signal is reconstructed from the audio ouput of the DSP, which is
then upconverted to 455 kHz, passed through a bandpass filter and buffered.
Note that it is different from the 455 kHz SMO output.
It can be used for further processing of exotic signals, e.g. by feeding it to
an external demodulator.
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IF Out 25 kHz IF output GND - Ground
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V.24 (RS232) / CSMA control port
A2J3
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For external control, the WJ-8711A has a standard RS232 (v.24) serial port.
The device supports both W-J's proprietary protocol, as well as ICOM's
CSMA, both of which are described in the manual.
Only three wires are needed: TX, RX and GND. There is no hardware handshake.
Instead it supports XON/XOFF and ACK/NACK software handshakes.
Below is the pinout of the 25-pin female DB25 socket at the rear of the
device, when looking into the receptacle.
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TX Out Data out (from WJ8711A) RX In Data in (to WJ8711A) - -
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GND - Ground
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Device Monitoring receiver Purpose Surveillance and spectrum monitoring Principle Triple conversion Model WJ-8711A Manufacturer Watkins-Johnson NSN 5826-01-473-2022 Country USA Years 1996-2010 Predecessor WJ-8711 Successor ? Frequency 5 kHz - 30 MHz Resolution 1Hz Waveforms see below Bandwidth 56 Hz - 16 kHz (66 steps) IF 40 MHz, 455 kHz, 25 kHz 1 DSP Motorola 56002 IP3 +30 dBm Memory 100 channels AGC Slow, Medium, Fast BFO 0-8000 Hz (in 10 Hz steps) Dimensions 508 × 482 × 133 mm Weight < 5 kg 2 Price US$ 20,486 (2023)
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Only the second IF is available as an output.
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Weight without preselector (5.4 kg with preselector).
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- AM
- Synchronous AM
- FM
- CW
- ISB
- USB
- LSB
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- Channel scan
- F1-F2 scan
- F1-F2 scan with lockouts
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WJ-871Y/REF High-stability reference oscillator WJ-8711/PRE Suboctave Preselector WJ-8711A/COR Varrier-Operated Relay WJ-8711/DSO1 Digital Signal Outout WJ-8711/488 IEEE-488 Interface (IEC-625, GPIB, HPIB) WJ-871Y/8KRF 8 kHz Roofing Filter WJ-871Y/485 RS-485 Interface WJ-871Y/SEU Speech Enhancement Unit WJ-871Y/IFC125 12.5 kHz IF Output WJ-871Y/FSK Frequecy Shift Keying WJ-8711/SPK Internal speaker WJ-8711/BFP Blank Front Panel
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- Digital HF Receiver WJ-8711A - brochure
Watkins-Johnson, May 1996.
- WJ-8711A - technical data sheet
Signia-IDT, 2003.
- WJ-8711A Digital HF Receiver - brochure
DRS Technologies, Inc. 2005.
- WJ-8711A - technical manual
Installation, Operation and Intermediate Level Maintenance Manual
for the WJ-8711A Digital HF Receiver.
DRS Signal Solutions, Inc., 1995. Revision March 2007. 1
- Type WJ-8711/PRE - Suboctave Preselector Option - technical manual
Signia-IDT, Inc., 2000. Rev. B, January 2003.
- Condor PSU SP1348A circuit diagram
DC Power Supplies Inc., 26 February 1993.
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Document kindly provided by Terry O'Laughlin [1].
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© Crypto Museum. Created: Sunday 30 March 2025. Last changed: Thursday, 03 April 2025 - 15:53 CET.
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