|
|
|
|
|
|
General coverage communications receiver
AR-88 was a valve-based shortwave
general coverage communications receiver,
developed and built in the early 1940s by the
Radio Corporation of America (RCA).
Although the receiver was initially intended as the successor
to the AR-77 amateur receiver, the outbreak of WWII made it evolve into
a professional high-end military-grade receiver for which cost was no
object [1].
|
The AR-88 is a 14-valve (tube) receiver, which covers a frequency
range of 535 kHz to 32 MHz.
Unlike the National HRO receiver,
which had pluggable coil packs for
each frequency band, the AR-88 uses a six-position
band selector.
A special version of the receiver, the AR-88LF, was suitable for LF
and MF, covering 70 to 550 kHz (continuously) and 1.5 to 30 MHz (continuously).
The image on the right shows a typical AR-88.
It measures 49 x 28 x 49 cm and weights over 40 kg.
Judging from its low serial number (100227) it was produced in the early
years of the war [1].
|
|
|
As most of the first production runs of the AR-88 was supplied to
Great Britain, Russia, France and China – as part of the 1941
lend-lease act [3] – it is likely that this one was used in the UK,
possibly inside a Y-Station, for intercepting German radio communications.
It has a black wrinkle paint finish, which was typical for the early models.
It was often supplied as an 'open frame' for mounting in a 19" rack,
but was also available as a closed cabinet with a hinged lid at the top,
as shown here.
Later versions came in a variety of colours and finishings, such as Naval grey.
It is estimated that a total of approx. 25,000 AR-88s
(all variants) were
built during the war [1].
After the war, the AR-88 became a popular receiver for radio amateurs,
who used them well into the 1960s. Some receivers are still being used
by amateurs and radio enthusiasts today. A typical feature on some of the
surviving AR-88 radios, is that most of them have an alternative
S-meter
behind the rightmost window on the front panel.
The reason for this is that during WWII, most receivers were shipped
without the original S-meter, due to world-wide shortages of such meters.
The receivers that were used for diversity reception didn't need an S-meter,
and the AR-88s used for interception in the UK were often equipped with an alternative meter
by the British. 1
|
 |
-
The device shown here has an S-meter that was supplied by the UK
Air Ministry (AM), which is an indication that it was probably
used in the UK [4].
|
The digram provides an overview of the controls at the front panel
of the AR-88. The device shown here is housed in a black metal enclosure,
which was optionally available. When mounted in a 19" rack, this cabinet
was usually omitted. The device could be powered by a wide range of mains
voltages, including 110 and 220V AC, making it suitable for worldwide
deployment. It is switched ON by setting the MODE selector at the bottom left
to the MOD or CW position.
When use as part of a radio station, the MODE selector can also be used
to control the transmitter.
The band selector is used to select one of six available
frequency bands, whereas the selectivity selector is used
to select the desired bandwidth between 1 (wide) and 5 (narrow). 1
The function of the Noise Limiter (NL) and the Automatic Volume Control (AVC) 2
can be controlled with the 4-position rotary selector at the bottom right.
|
-
Here known as broad and sharp respectively.
-
Also known as Automatic Gain Control (AGC).
|
- AR-88
- AR-88D
- AR-88F
- AR-88LF
|
|
|
|
|
During WWII, the British intelligence service,
GC&CS (now: GCHQ),
ran a massive operation for intercepting and decoding German radio
messages in morse code, under the codename
ULTRA. The majority of the intercepted messages
— picked up by a network of so-called Y-Stations —
were encrypted with the
Enigma cipher machine, which was
regarded unbreakable at the time.
|
The Y-Stations were spread all over
the UK, but were also present in other parts of the world, including
North Africa and Australia. They were operated around the clock by the
so-called Y-Service, which consisted mainly of HAM radio operators and
specially trained house wifes, using
intercept receivers like
HRO-5 and AR-88.
Once the messages were intercepted, they were sent to the codebreaking
center at Bletchley Park by despatch rider or via
teleprinter lines (telex).
There, a team of over 12,000 people,
broke the German codes at a large scale on a daily basis.
|
|
|
As many receivers were required for the war effort, the UK ordered
large quantities of AR-88 receivers from 1941 onwards.
These were provided by the US under the so-called lend-lease act
of October 1941 [3].
The receivers were supplied as stand-alone as well as rackmount units.
|
The image on the right shows an intercept room at
Beaumanor Hall, one of the most prominent Y-Stations in the UK.
In the room, an long array of intercept desks was present,
each with its own operator. The image on the right shows a single
desk with the necessary paperwork and a pair of headphones.
At the right is a 19" rack with two RCA
AR-88 receivers.
The device at the front left is a so-called undulator,
a recording device that could write morse code as a series
of square waves onto a strip of pre-gummed paper.
The intercept rooms were located in the main building
(Beaumanor Hall) as well as in a series of wooden huts, disguised
as stables and cricket pavilions. Other receivers were used here
as well. The signal from the various antennas were distributed
to all receivers on the estate [6].
Per lend-lease agreement, the receivers had to be returned to the US
or destroyed, when they were no longer needed.
For that reason, many AR-88s were destroyed at the end of the war.
|
|
|
This is probably the
reason why so few AR-88s are found today. The ones that did survive
were often bought back by the UK (for a fraction of the actual price)
after they had been returned 'pro-forma'.
The manufacturer – RCA –
didn't want to see any of them back again on the US market.
|
The AR-88 also played an important part in intercepting German
Wireless Traffic (WT) that originated from the
Lorenz SZ-40/42 cipher machine.
The SZ-40/42 was codenamed TUNNY by the allies, and was in fact a heavy
mechanical coding machine with 12 cipher wheels, that was used for
the encryption of teletype traffic (telex).
The telex signals were first encrypted using the SZ-40,
and then sent via short wave radio, using Frequency Shift Keying (FSK).
At the other end the traffic was decrypted using another SZ-40.
|
|
|
In the UK, the German signals were intercepted by the various Y-Stations,
and sent to Bletchley Park (BP) for decoding.
At BP, a team of mathematicians led by Bill Tutte, managed to create
a working electronic equivalent of the TUNNY machine, without ever having
seen a real Lorenz SZ-40. Unlike the mechanical SZ-40, the TUNNY machine
used electronic valves (tubes).
The image above shows Sarah Marlin and Debby Minney in ATS uniform,
re-enacting the intercept of TUNNY traffic at the Tunny Gallery opening
day at The National Museum of Computing in May 2011 [8].
|
In Great Britain, the AR-88 was not only used for interception of
enemy radio signals, but also for communication with ships and
airplanes. The photograph on the right was taken in the secret
Underground Headquarters (UGHQ) under Fort Southwick,
hidden deep down in the Portsdown Tunnels [5].
On D-Day, this was the Allied communications center for
Operation Overlord.
An AR-88 is visible on the left,
being operated by a WRENS (Womens Royal Navy Service).
The clothing of the other operators suggest that this was
the Naval wireless transmission room (W/T).
|
|
|
Portsdown is located to the north of Portsmouth (UK). It consists of
approx. 5 miles of tunnel constructions, hidden in a 120 metres high
chalk hill that is locally known as The Hill.
Most of it was created during WWII.
More information about the underground headquarters (UGHQ),
the Portsdown Tunnels and Fort Southwick,
is available from Bob Hunt's excellent website [5].
|
Below is the simplified block diagram of the AR-88. At the left is a 2-stage
RF pre-amplifier built around two 6SG7 valves, the output of which is mixed in a
6SA7 with the signal from a VFO built around a 6J5.
The VFO is adjusted in tandem with the tuned circuits of the RF
pre-amplifiers.
The output of the mixer is followed by a selectable bandwith filter
and several IF amplifier stages (3 x 6SG7),
each of which has selectable band-pass filters to increase the
overall selectivity of the receiver.
The signal is then fed to an AM detector (½ 6H6) followed by a limiter
(6H6), an audio pre-amplifier (6SJ7),
and finally a power amplifier stage (6K6GT).
For the reception of CW signals (morse code),
the signal from a BFO (6J5) can be injected at the input of the
third IF amplifier.
An Automatic Gain Control (AGC) – built around ½ 6H6 – takes its input from
the detector and various IF stages, to ensure that the two RF amplifier
stages (RF1, RF2) are not overloaded when receiving strong signals.
Two further valves – a 5Y3GT double rectifier and a VR-150 stabiliser –
are used in the mains power supply unit (PSU)
and are not shown in the above block diagram.
|
The original circuit diagram [B]
– extracted from the original instruction manual [A] –
is available for download below. However, due to the complexity of the
selectable band-pass filters
– which affect nearly every stage of the receiver –
it is cluttered with lines and rotary switches, and might therefore
be difficult to understand.
For this reason, the Dutch Radio Monitoring Service (RCD)
made its own circuit diagram in 1958,
in which the bandwidth selectors are omitted [C].
The simplified circuit diagram also shows an additional EF80 valve,
which is used as a cathode follower. It buffers the output of the mixer
and provides an output for a panoramic display (panadapter) that can
be connected externally. This was probably a modification by the RCD.
➤ Original circuit diagram
➤ Simplified circuit diagram
|
Frequency 535 kHz - 23 MHz Bands 6 (see below) IF 455 kHz Impedance 200Ω 1 Antenna 7.5-15 m (25-50 ft.) Sensitivity < 1µV at 0.5W output Selectivity 5 positions (see below) Output 2.5W into 2.25Ω or 600Ω 2 LT 6V, 4A HT 250-300V, 90mA Mains 100-165V or 190-260V AC 50/60Hz Valves 14 (see below) Dimensions 489 x 489 x 279 mm Weight 40 kg NSN 5820-17-601-6969
|
-
Except on lowed frequency band (535 kHz - 1.6 MHz).
-
Receivers with S/N below 00300 have 20Ω output instead of 600Ω.
|
6SG7 (5x) RF amplifier, IF amplifier 6SA7 Mixer 6J5 (2x) LO, BFO 6H6 (2x) 2nd detector, Noise limiter 6SJ7 AF Amplifier 6K6GT AF Power Amplifier 5Y3GT Rectifier VR-150 Voltage Regulator
|
- 535 kHz - 1.6 MHz
- 1.6 - 4.5 MHz
- 4.5 - 12 MHz
- 12 - 16.5 MHz
- 16.5 - 22.5 MHz
- 22.6 - 32 MHz
|
|
|
Selectivity settings
at -6dB
|
|
|
- ~ 13 KHz/s
- ~ 7 kHz
- 3 kHz
- 1500 Hz
- 400 Hz
|
- General Purpose Communications Receiver Model AR-88D, Instructions
RCA, Camden (NJ, USA). IB-25927-3. Amended 26 November 1943.
- AR-88 Circuit Diagram
RCA, Camden (NJ, USA). IB-25927-3. Amended 26 November 1943.
This circuit diagram should be inserted as Page 21 of the manual [A].
- RCD Communication Receiver AR 88, simplified circuit diagram
RCD (NL), 2 July 1958.
- Reception Set AR-88, Description (provisional)
Electrical and Mechanical Engineering Regulations. E-752. Issue 1, May 1945.
- AR-88, Promotional poster
RCA, RL 13701-S. Date unknown.
|
- Henry Rogers, RCA's Amazing AR-88 Receivers
Website: Radio Boulevard. Western Historic Radio Museum.
1997-2012. Retrieved December 2012.
- Wikipedia, RCA (Radio Corporation of America)
Retrieved December 2012.
- Wikipedia, WWII Lend-Lease Act
Retrieved December 2012.
- Cor Moerman, AR-88 Receiver - THANKS !
RCA AR-88 receiver featured on this page kindly donated by Museum Jan Corver.
Budel (Netherlands), December 2012.
- Bob Hunt, Portsdown Tunnels
Website, Retrieved December 2012.
- Kevin Coleman, Personal correspondence
Volunteer at Bletchley Park (Station X) and Beaumanor (Y-Station).
December 2008 - January 2009.
- The National Archives, Image of radio intercept room at Beaumanor Hall
National Archives (UK) reference: HW41-119.
- John Robertson, Photograph of Y-Station re-enactment
The National Museum of Computing (TNMOC), TUNNY Gallery opening day,
26 May 2011.
|
|
|
|
Any links shown in red are currently unavailable.
If you like the information on this website, why not make a donation?
© Crypto Museum. Created: Wednesday 05 December 2012. Last changed: Friday, 26 May 2023 - 21:03 CET.
|
|
|
|
|
![RCA AR-88, kindly donated by Museum Jan Corver [4].](img/301655/004/full.jpg)
![Radio intercept room at Beaumanor Hall, showing several AR-88 receivers. The National Archives HW41-119 [7].](img/beaumanor_01.jpg)
![Re-enactment at TNMOC during the Tunny Gallery opening day [8]](img/tnmoc_tunny_rx.jpg)
![AR-88 in use in the Naval Wireless Transmission room of the Underground Headquarters during WWII. Reproduced here by kind permission from Bob Hunt [5].](img/portsdown.jpg)
