Pip-squeak was a
radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination.
The basic principles a ...
system used by the British
Royal Air Force
The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...
during the early part of
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. Pip-squeak used an aircraft's voice radio set to periodically send out a 1 kHz tone which was picked up by ground-based
high-frequency direction finding
High-frequency direction finding, usually known by its abbreviation HF/DF or nickname huff-duff, is a type of radio direction finder (RDF) introduced in World War II. High frequency (HF) refers to a radio band that can effectively communicate over ...
(HFDF, "huff-duff") receivers. Using three HFDF measurements, observers could determine the location of friendly aircraft using
triangulation
In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points.
Applications
In surveying
Specifically in surveying, triangulation involves only angle me ...
.
Pip-squeak was used by
fighter aircraft
Fighter aircraft are fixed-wing military aircraft designed primarily for air-to-air combat. In military conflict, the role of fighter aircraft is to establish air superiority of the battlespace. Domination of the airspace above a battlefield ...
during the
Battle of Britain
The Battle of Britain, also known as the Air Battle for England (german: die Luftschlacht um England), was a military campaign of the Second World War, in which the Royal Air Force (RAF) and the Fleet Air Arm (FAA) of the Royal Navy defende ...
as part of the
Dowding system
The Dowding system was the world's first wide-area ground-controlled interception network, controlling the airspace across the United Kingdom from northern Scotland to the southern coast of England. It used a widespread dedicated land-line telep ...
, where it provided the primary means of locating friendly forces, and indirectly providing
identification friend or foe (IFF). At the time,
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
systems were sited on the shore and did not provide coverage over the inland areas, so IFF systems that produced unique radar images were not always useful for directing interceptions. Pip-squeak was added to provide coverage in these areas. As more radar stations were added and over-land areas became widely covered, pip-squeak was replaced by IFF systems of increasing sophistication.
Pip-squeak gets its name from a contemporary
comic strip
A comic strip is a sequence of drawings, often cartoons, arranged in interrelated panels to display brief humor or form a narrative, often serialized, with text in balloons and captions. Traditionally, throughout the 20th and into the 21st ...
,
Pip, Squeak and Wilfred
''Pip, Squeak and Wilfred'' was a British strip cartoon published in the ''Daily Mirror'' from 1919 to 1956 (with a break c. 1940–1950), as well as the ''Sunday Pictorial'' in the early years. It was conceived by Bertram Lamb, who took the role ...
. It was first implemented in the TR.9D radio. The system was also used by the
USAAF
The United States Army Air Forces (USAAF or AAF) was the major land-based aerial warfare service component of the United States Army and ''de facto'' aerial warfare service branch of the United States during and immediately after World War II ...
, where the equipment was known as RC-96A.
Background
Before radar
By the middle of 1930, the
Air Defence of Great Britain
The Air Defence of Great Britain (ADGB) was a RAF command comprising substantial army and RAF elements responsible for the air defence of the British Isles. It lasted from 1925, following recommendations that the RAF take control of homeland air ...
(ADGB) command of the
Royal Air Force
The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...
was planning its response to the threat of air attack. This involved the construction of a large number of
acoustic mirror
An acoustic mirror is a passive device used to reflect and focus (concentrate) sound waves. Parabolic acoustic mirrors are widely used in parabolic microphones to pick up sound from great distances, employed in surveillance and reporting of ...
s to provide early warning, along with a network of observer stations that would soon be arranged into the
Royal Observer Corps
The Royal Observer Corps (ROC) was a civil defence organisation intended for the visual detection, identification, tracking and reporting of aircraft over Great Britain. It operated in the United Kingdom between 29 October 1925 and 31 December ...
(ROC). The system would provide defence around the
London
London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a majo ...
area only, starting on the coast from
Suffolk
Suffolk () is a ceremonial county of England in East Anglia. It borders Norfolk to the north, Cambridgeshire to the west and Essex to the south; the North Sea lies to the east. The county town is Ipswich; other important towns include Lowes ...
to
Sussex
Sussex (), from the Old English (), is a historic county in South East England that was formerly an independent medieval Anglo-Saxon kingdom. It is bounded to the west by Hampshire, north by Surrey, northeast by Kent, south by the English ...
with a thin belt of
anti-aircraft artillery
Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based, ...
, a fighter operating area inland, and a second group of guns in or near the city. The system was basically unchanged in operation from its World War I counterpart, but greatly expanded the area allotted to the fighters.
In tests carried out primarily from
Biggin Hill during the mid-1930s, the expanded fighter operating area demonstrated a serious problem keeping track of friendly forces. Especially as altitudes increased or the weather grew more cloudy, observers could no longer keep track or identify fighters. This made it impossible for the centralized control and tracking centres to properly direct the fighters to their targets. Radio location was noted as a solution to this problem early on.
Huff-duff
Shortly after taking over command of the ADGB system and combining it into the main
Fighter Command
RAF Fighter Command was one of the commands of the Royal Air Force. It was formed in 1936 to allow more specialised control of fighter aircraft. It served throughout the Second World War
World War II or the Second World War, oft ...
network,
Hugh Dowding
Air Chief Marshal Hugh Caswall Tremenheere Dowding, 1st Baron Dowding, (24 April 1882 – 15 February 1970) was an officer in the Royal Air Force. He was Air Officer Commanding RAF Fighter Command during the Battle of Britain and is generally c ...
made the installation of
high-frequency direction finding
High-frequency direction finding, usually known by its abbreviation HF/DF or nickname huff-duff, is a type of radio direction finder (RDF) introduced in World War II. High frequency (HF) refers to a radio band that can effectively communicate over ...
, or "huff-duff", sets a priority. In the summer of 1937 he requested that every sector be equipped with three huff-duff sets in order to allow rapid triangulation of the location of fighters. Coincident with this was the deployment of the latest version of the widely used TR.9 radio set, the TR.9B.
The Air Staff was slow to respond to Dowding's request due to a shortage of
cathode ray tube
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms ( oscilloscope), pictu ...
s (CRTs) used in the huff-duff sets, and by the end of 1937 only five sectors were equipped. During tests in March 1938, the value of DF as part of the reporting system became very clear to all involved, and on 14 April 1938 the Air Ministry ordered a further 29 sets to equip all sectors. These were initially delivered without a CRT and required longer to reliably determine direction using a manual
radiogoniometer, but were designed to be upgraded as CRTs arrived.
Pip-squeak
Throughout 1938, the
Royal Aircraft Establishment
The Royal Aircraft Establishment (RAE) was a British research establishment, known by several different names during its history, that eventually came under the aegis of the Ministry of Defence (United Kingdom), UK Ministry of Defence (MoD), bef ...
worked on a new version of the TR.9 set, the "D" model, which was designed specifically to aid DF operators. This model included a single transmission amplifier, but two radio frequency oscillators, allowing the set to be quickly switched between two broadcast frequencies. Using one for voice and the other for DF, aircraft could broadcast a DF signal on the separate channel without disrupting other aircraft's communications on the voice channel.
Key to the system was the addition of a tone-generating oscillator that produced a 1 kHz tone, the "squeak". When keyed into the TR.9D's transmitter, it produced a distinctive tone that was easy to locate on the huff-duff sets. To further improve operation, an automatic switch was installed that switched the radio to the DF broadcast frequency and turned on the oscillator, then turned it back off again after a set period. To indicate that the system was active, the same 1 kHz tone was also played into the pilot's headphones, at a muted level.
Introduction of IFF
Some experimental use of IFF systems had taken place as early as 1936, but these passive "reflector" systems proved almost useless. An active
transponder
In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend word, blend of ''transmitter'' and ''responder''.
In air navigation or radio frequency identification, a T ...
system based around a
regenerative receiver
A regenerative circuit is an amplifier circuit that employs positive feedback (also known as regeneration or reaction). Some of the output of the amplifying device is applied back to its input so as to add to the input signal, increasing the am ...
had been introduced in 1939,
but demonstrated problems with
gain
Gain or GAIN may refer to:
Science and technology
* Gain (electronics), an electronics and signal processing term
* Antenna gain
* Gain (laser), the amplification involved in laser emission
* Gain (projection screens)
* Information gain in de ...
settings and had the disadvantage that it could only work with the Chain Home radars.
These problems were addressed in the
IFF Mark II, which had an
automatic gain control
Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the inpu ...
and several internal receivers that could respond to any of the popular radars of the era. Mark II was a great advance, but it became available in 1940 just as the Battle of Britain was opening. Deliveries were forced to wait until the Battle ended, at which point they were rapidly installed across much of the RAF fleet.
IFF theoretically made pip-squeak redundant, but a lack of radar coverage over inland areas kept it in use. New radars, notably the
AMES Type 7
The AMES Type 7, also known as the Final GCI, was a ground-based radar system introduced during World War II by the Royal Air Force (RAF). The Type 7 was the first truly modern radar used by the Allies, providing a 360 degree view of the airspace a ...
, began to fill in these areas through 1941. Pip-squeak remained in use after this period as an emergency navigation system in the case when an aircraft was lost, allowing the ground operators to locate an aircraft using their voice radios.
Description
Broadcaster
Pip-squeak's airborne unit consisted of two primary parts, an oscillator to produce a whistle at 1 kHz, and a mechanical clock with electrical contacts to periodically switch the oscillator and DF broadcast channel on and off. Using the TR.9D, the most common radio during the early stages of the war, there were two available channels, and the frequencies were selected before the mission using swappable
crystal oscillator
A crystal oscillator is an electronic oscillator circuit that uses a piezoelectric crystal as a frequency-selective element. The oscillator frequency is often used to keep track of time, as in quartz wristwatches, to provide a stable cloc ...
s. Both the section leader and one other aircraft in the section normally had pip-squeak aboard.
Shortly after forming up after a scramble, the squadron leaders would be asked to ready their pip-squeak clocks. In the original system this required them to turn the "wind" knob that moved the single second-hand counter-clockwise around the face of the clock. There were up to four sections of aircraft in each squadron, although most squadrons had two or three sections at any given time. Each section had its own position for the hand; red section had the 12 o'clock location, yellow was at 9 o'clock, blue at 6 o'clock and green at 3 o'clock.
Once the clocks were properly positioned, the sector controller would initiate a countdown, ''Synchronize time, 5, 4, 3, 2, 1, mark''. At mark, the pilots would turn on the clock, which would start the second hand moving clockwise. When the hand reached the 12 o'clock position the oscillator was automatically turned on, and it turned off again just before the 3 o'clock position, broadcasting for 14 seconds per minute. The system also automatically switched the radio from voice to pip-squeak channel at the 12 o'clock location; if the pilot was talking he would be cut off.
Red section, having started in the 12 o'clock position, started broadcasting immediately when the system was activated. When it stopped 14 seconds later, yellow section's clock was now reaching the 12 o'clock position and began to broadcast, and so forth. Over a one-minute period, all four sections (if present) squeaked and could be located.
A separate radio control switch stopped the radio signal from broadcasting while the clock continued to move. This allowed the pilot to set up the system early in the flight, and then turn it off when better communications were needed, like in combat. The system could then be turned on again at any time, with the clock still in the proper position. Sector Commanders could ask pilots to turn it on by asking "Is your Cockerel crowing?".
There were two common versions of pip-squeak, one with the clock located in the cockpit, and a second that used a remote clock system.
[For an image of the "single unit" version, see Colin MacKinnon]
"Radio Identification Systems – Identification, Friend or Foe"
VK2DYM'S Military Radios The later placed the "Master Contactor" in a box in the equipment bay near the radio, and it was pre-set to the correct second-hand location for each section, prior to the mission. The "Remote Contactor" display was located in the cockpit, driven by electrical signals from the Master Contactor, whose once-per-second signals powered a
stepper motor
A stepper motor, also known as step motor or stepping motor, is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any pos ...
driving the second hand. This version had only a single control to turn the clock on and off to start it up at "mark", a separate switch on the radio console allowed the signal to be stopped and started while leaving the clock running.
Plotting
Each sector was equipped with three huff-duff sets for determining the location of the pip-squeak radios. Although in theory only two were needed, adding a third offered redundancy as well as helping reduce the chance of errors in the plotting. The stations were positioned approximately apart in as close to an equilateral triangular layout as possible. One of the three stations was co-located at the Sector Control center, with the two remote stations communicating with the center over telephone lines.
At the Sector Control, a simple system was used to rapidly take a
"fix". This consisted of a circular plotting board with a map on the top surface marked with the
Ordnance Survey National Grid
The Ordnance Survey National Grid reference system (OSGB) (also known as British National Grid (BNG)) is a system of geographic grid references used in Great Britain, distinct from latitude and longitude.
The Ordnance Survey (OS) devised the ...
, and a series of compass angles on a
protractor
A protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles.
Some protractors are simple half-discs or full circles. More advanced protractors, such as the bevel protractor, have one or two sw ...
around the outer edge. The location of the three stations was represented by small holes drilled into the map. Weighed strings passed through the holes, and could be pulled up and across the map by the plotters. When a report was received from a huff-duff operator, the plotter would pull their string so it lay on the indicated angle; the weight (or elastic cord) on the other end kept the string taut.
With the three reports plotted, the strings would normally intersect at a small triangle or star somewhere on the map. This location was read against the Grid. The operators could identify which section they were tracking simply by looking at a
sector clock
A Sector clock or colour change clock was a round colour-coded clock used at military airfields and observation posts in the United Kingdom to help track the movements of enemy aircraft and control friendly aircraft.
History
Originally known a ...
painted with section colours, as the sections had manually synchronized their clocks with this one. A fourth operator observing the plots would then call in the position to the main operations room. The system required fast operations by all involved, as they had only 14 seconds to make a plot before the next section reported in.
When the grid location was passed to the operations room, a marker for that section could be updated on the sector's plotting table. Pip-squeak did not directly produce
identification friend or foe (IFF) information, but served that purpose in practice by allowing the operators to determine which plots were friendly. This might be used, for instance, when reports from radar or ROC observers were tracking friendly forces without knowing it.
Problems
Although pip-squeak worked well in practice and could be used with any aircraft with a radio, it presented several practical problems that led to its eventual replacement.
The first was that the system used up a radio channel. As the TR.9D set had only two channels, using one for pip-squeak left only a single voice channel. All of the aircraft in the squadron shared the same frequencies for voice and pip-squeak, selected before the mission. This meant that squadrons could talk amongst themselves and to their Sector Operator, but could not coordinate with other squadrons or Sectors. Pilots were also constantly being interrupted. Things improved with the introduction of the TR.1388 sets, which had several voice channels and much longer range, but pip-squeak still interrupted the pilot when it broadcast.
Further, the pip-squeak system required an entirely separate reporting chain, along with the associated equipment, buildings, manpower and telephone systems. This information was primarily consumed by the Sector Controls, who had the responsibility for vectoring fighters onto targets, and thus required up-to-date information on the locations of their fighters. This meant that information about the location of friendly forces had to be sent back up the chain to Group and Fighter Command Headquarters, increasing the amount of traffic flowing through the system.
Pip-squeak was supplanted, and then replaced, by the
IFF
In logic and related fields such as mathematics and philosophy, "if and only if" (shortened as "iff") is a biconditional logical connective between statements, where either both statements are true or both are false.
The connective is bicon ...
system. This was a self-contained
transponder
In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend word, blend of ''transmitter'' and ''responder''.
In air navigation or radio frequency identification, a T ...
that was triggered by the signal of a radar being received by the aircraft. The transponder sent out a short radio pulse of its own when the radar signal was received. This signal was filtered out and sent to a separate amplifier at the radar station. The output was then mixed with the main signal and caused an upside-down blip to be displayed slightly after the main signal. This "secondary" return now gives its name to
secondary radar
Secondary surveillance radar (SSR)''Secondary Surveillance Radar'', Stevens M.C. Artech House, is a radar system used in air traffic control (ATC), that unlike primary radar systems that measure the bearing and distance of targets using the d ...
, which forms the basis of most civilian radar systems.
IFF had been produced as early as 1939, but not widely used because the early
Chain Home
Chain Home, or CH for short, was the codename for the ring of coastal Early Warning radar stations built by the Royal Air Force (RAF) before and during the Second World War to detect and track aircraft. Initially known as RDF, and given the off ...
radar stations were placed along the shoreline, providing no coverage inland where much of the action took place. By 1942 the radar network had been extensively updated, especially with the introduction of the
ground-controlled interception Ground-controlled interception (GCI) is an air defence tactic whereby one or more radar stations or other observational stations are linked to a command communications centre which guides interceptor aircraft to an airborne target. This tactic was p ...
units, and the plotting of interceptions moved from the Sector Controls to the radar sets themselves. IFF was universal by this point.
References
Citations
Bibliography
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External links
Video of an opened Master Contactor
Battle of Britain
Science and technology during World War II
World War II British electronics
Radar networks