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General coverage communications receiver

The AR-88 was a valve-based shortwave general coverage communications receiver, developed and built by the Radio Corporation of America (RCA) in the early 1940s. 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].
RCA AR-88, kindly donated by Museum Jan Corver [4].

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, for example for intercept work. It is finished in black wrinkle paint, which was typical for the early models. It was often supplied as an 'open frame' for 19" rack-mount purposes, but could also come as a cased version, in which case the 19" radio was built inside a black wrinkle paint cabinet with a lid in the top panel. Later versions came in a variety of colours and finishings (e.g. 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 using for interception in the UK were often equipped with an alternative meter by the British.
RCA AR-88 receiver Front view of the AR-88 AR-88 with opened top lid Filters inside the AR-88 Frequency scale and S-meter Frequency band scales Frequency fine tuning S-meter

Frequency ranges
  1. 0.54 - 1.6 MHz
  2. 1.6 - 4.5 MHz
  3. 4.5 - 12 MHz
  4. 12 - 16.5 MHz
  5. 16.5 - 22.5 MHz
  6. 22.6 - 32 MHz
Wartime use
During WWII, the British intelligence service, GC&CS (now: GCHQ), ran a massive operation of intercepting and decoding German radio messages in morse code, mainly encrypted using the well-known Enigma cipher machine. The messages were intercepted by the so-called Y-Stations.
These Y-Stations were spread all over the country, but were also present in other parts of the world, such as North Africa and Australia. Those Y-Stations were operated by Ham Radio operators and specially trained house-wifes, the so-called Y-Service, using a variety of intercept receivers, such as the AR-88 and the HRO.

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.
Bletchley Park, Britain's wartime codebreaking center.

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].

The lend-lease agreement commanded that the receivers had to be returned or destroyed when they were no longer needed. Many AR-88s were therefore destroyed after WWII had ended.
Radio intercept room at Beaumanor Hall, showing several AR-88 receivers. The National Archives HW41-119 [7].

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 formally been returned. The manufacturer, RCA, didn't want to see any of them back on the US market again.
The AR-88 also played an important part for intercepting German Wireless Traffic (WT) that was created with the Lorenz SZ-40/42 cipher machine. The SX-40/42 was known as 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.
Re-enactment at TNMOC during the Tunny Gallery opening day [8]

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 methematicians 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).
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].

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].
  • AR-88
  • AR-88D
  • AR-88F
  • AR-88LF
  • CR-88
  • CR-88A
  • CR-88B
  • CR-91
  • CR-91A
  • SC-88
  1. Henry Rogers, RCA's Amazing AR-88 Receivers
    Website: Radio Boulevard. Western Historic Radio Museum.
    1997-2012. Retrieved December 2012.

  2. Wikipedia, RCA (Radio Corporation of America)
    Retrieved December 2012.

  3. Wikipedia, WWII Lend-Lease Act
    Retrieved December 2012.

  4. Museum Jan Corver, AR-88 Receiver - THANKS !
    RCA AR-88 receiver featured on this page kindly donated by Museum Jan Cover.
    Budel, The Netherlands.

  5. Bob Hunt, Portsdown Tunnels
    Website, Retrieved December 2012.

  6. Personal correspondence with Kevin Coleman
    Volunteer at Bletchley Park (Station X) and Beaumanor (Y-Station).
    December 2008 - January 2009.

  7. The National Archives, Image of radio intercept room at Beaumanor Hall
    National Archives (UK) reference: HW41-119.

  8. John Robertson, Photograph of Y-Station re-enactment
    The National Museum of Computing (TNMOC), TUNNY Gallery opening day, 26 May 2011.

Further information

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Crypto Museum. Created: Saturday 05 December 2015. Last changed: Saturday, 24 December 2016 - 20:25 CET.
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