As a preface to this subject, we need to remind ourselves of the important role Morse played in the Navy prior to RATT [ASHORE] and between it and RATT [AFLOAT].  To start with, Morse was made by hand and received by a pen-inker.  The earphone [telephones as they were called] was invented and operators started to copy the Morse with a pencil and a piece of paper.  Automation followed several years later and 'hand speed Morse' was re-defined as Morse made by hand key or by autohead, and when made by the latter, a new skill of Morse-Typing was required not to mention the issue of hundreds of typewriters to the Fleet.  From the mid-1920's, W/T transmitters were made capable of transmitting high speed Morse {100 to 120 wpm} and the Undulator was employed on these circuits. Huge amounts of traffic could be cleared in a relatively short time period, but that was only a true asset for the transmitter end, for it left the receiving operator with the unenviable task of transcribing 'miles' of paper tape back into a form usable for a communications link. Its only practical use was that it shortened the time on air and therefore lessened the chance of being D/F'ed by the enemy, so, by definition, the practicality for shore-shore circuits was not obvious.  By the time WW2 started, the undulator was used on many circuits to and from sea and shore to shore fixed-services, employing [shore side] hundreds of Wrens who did little more than hand transcribe paper tapes.  Machines to do this had of course been invented, but by and large the system remained cumbersome and man/women-power intensive. Then, in 1940, the Navy launched what was to be its last 'Morse Transcribing Unit'.  It was one of the unsung hero's of the war, because in proving its worth it released precious man/woman-power for other important duties, but also allowed the conduct of the war greater latitude by increasing critical traffic space.  These high speed Morse fixed services, say between the Admiralty {Whitehall} and Malta {Lascaris} conveying a signal between two Admirals, fulfilled the requirement, but if Malta were to send a message {via Whitehall} destined for Singapore, the real problem began because each and every relay station would have to do the transcription bit before passing on the message. Automation at the relaying points was a high priority war target, but this would only work with a code where each letter/figure was of exactly the same length: Morse, as we know, had units which were anything but where a DASH was three times longer than a DOT. Landlines, signalling with DC voltages and not radio waves had long been using the 5-unit Murray Code where indeed each character is of the same length whether it be a full stop, an oblique stroke or the letter P.  The long war was prosecuted relying chiefly upon the Morse Code at 'hand speed' or at 'high speed', and it wasn't until 1946 time that RATT took over from Morse on the fixed services. At this point, page copies were no longer important but representative paper tapes were,  for it was these which were used to deliver the message to its final destination.  Thus the new system became known as "TAPE RELAY".  These files show the SHORE RATT situation in 1965 NAVAL WORLD WIDE STRATEGIC COMMUNICATIONS NETWORK.pdf and STATION GROUPS.pdf.

Here is a little file showing the working of the Morse Transcribing Unit MORSE TRANSCRIPTION UNIT.pdf, and this small file tells us about mass-training {at the beginning of the war when hundreds of men are joining the navy daily} of 50 men at a time being trained in the skills of sending and receiving the Morse Code MORSE TEACHER UNIT.pdf.

The use of Morse Code continued unabated at sea and although the undulator had been consigned to the scrap metal pile, its speeds varied as follows.  In periods of high operational traffic {Berlin Air Lift, Korean War, Suez War} the conventional autohead,  with its proverbial PARIS tape,  was nudged towards the 28-30wpm mark.  The affects of this on the W/T branch are difficult, nay impossible, to put into words, but a good analogy is that of the fighter pilot versus the pilot of a lumbering transport plane. When the speed of the Broadcast was 22wpm [the norm] the transport plane pilot coped well with the pressure, but when it was increased, the operator lived on his wits, rather like a fighter pilot does. The other occasion of increasing the speed of Morse Code was to lessen the time a submarine needed to be at periscope depth to get her traffic.  The boat would come shallow to periscope depth [a dangerous depth for any boat even in peace time] read the traffic list sent by hand, ascertain from this whether there was needed traffic [new and missed numbers], go deep if the answer was no but if the answer was yes, she would record the high speed Morse and then go deep, playing back the Morse by slowing down the recorder for approximately 20 wpm. These submarine high speed Morse Broadcast Routines continued right through the 1960's and into the very early 1970's as hand-transcriptions, which were followed by the AN/UGA [a USN piece of equipment] which converted the high speed Morse into a RATT signal to be read on a teleprinter and not on a piece of signal pad.


To introduce this subject, I want you to think about the time before the JCB {and other mechanical tools} were introduced, when men {navvies} would dig holes using their muscle power with a pick and a shovel.  The work was hard and slow of course, and when lots of holes had to be dug, lots of navvies were employed in gangs.   The JCB did the job with just one man controlling it and in the beginning the navvies stood around and watched in wonderment at the modern ways of hydraulics, conscious that their muscle power might be called upon should the 'machine' fail and come to a grinding halt.  Not long after they were out of a job because the 'machine' proved its worth and its reliability was not an issue: the JCB increased the 'work-done' many fold but hugely lessened the human input.  There is a clear and direct analogy to these men and machines, because before RATT was introduced at sea {RATT being analogous to the JCB}, telegraphists [navvies] worked extremely hard throughout each and every watch to receive and send signals, their dexterity, high intelligence, focused mind and brain, being the equivalent of the navvies strength and endurance.  When the traffic levels were high {more holes required to be dug} the answer was to employ more telegraphists by changing from a four or three watch system to defence watches [watch and watch about] or to speed up the Morse code which added even more stress to the operators and the system.  When RATT was first introduced, the stresses and strains manifest in a telegraphists duty were not immediately lifted because the navy ran RATT and Morse together, side by side, as a 'belts-and-braces' approach just in case the 'machine - RATT equipment' failed to live up to expectations.  When things were working well,  the traffic flow increased because of the speed of operating with the teletypewriters {? but see below} - just like the JCB got through more work.  In actual fact, the speed more than doubled [Fleet speed on Morse Broadcast was often 25wpm = 18.75 Bauds] and the new Fleet RATT was set at 45 Bauds [later increasing to 50 and/or 75 bauds] = 66.6 and/or 100 wpm.  Add to this the convenience of having a teletypewriter copy of the signal rather than a hand scribed copy and the effect of speed was even greater in reality. However, the early teletypewriter was most unreliable and couldn't in any event be set to receive on a greater speed than 45 bauds. Remember also that on-line cryptography was still not at sea so many of the messages [in and out] were still in five-letter code format coded by the Type X/CCM machine or by the newly introduced KL7 Adonis machine. Out of sequence I know and we will see this picture again, but let's jump to this file/photograph of the early 'belts-and-braces' RATT set up. Click HERE. At this stage we will concentrate on HF only which involves Broadcast reception only,  and all we want you to observe are the five receivers <four top shelf and one middle shelf upper >, three of which {2 x B40 and 1 x B41} are devoted to RATT, and two {1 x B40, 1 x B41} for CW.  The middle teletypewriter [just the one] is used to print the Fleet RATT Broadcast and the ordinary typewriter over to the right is used by the telegraphist to type the Fleet CW Broadcast.

I can think of no better way of describing the pre RATT era, a prerequisite to understanding  RATT and its advantages, than by pointing you to this link which tells the story of a near disaster at a time when Britain and the Royal Navy were under the greatest of pressures fighting the Suez War of 1956:  we could have lost simply because our communications were stretched to the point of breaking. Have a look here   http://www.godfreydykes.info/SUEZ%201956%20THE%20MORSE%20CODE%20YEARS.htm.

By 1955 Radio Teletype was a well established way of communicating globally and land line teleprinter/teletypewriter working was 'old-hat', it having been in use for so many years. Naval Shore W/T Stations, serving foreign based RN Communication Centres [COMMCENS], were providing RATT Circuits [Fixed Services] and apart from engineering, all communication between these stations was done using teleprinter/teletypewriter page copies and perforated 5-Unit Murray Code torn-tape platforms, the only Morse code circuits being to and from ships in their area, or to/from ships using the international CW ship-shore organisation. Using various machines, 5UCO is one of them, traffic could be passed in plain language {P/L} between stations on-line leaving only special handling traffic to be encoded/decoded off-line. Ships, both incoming and outgoing used only Morse code for their main traffic flows, and R/T for other communicating needs, but of course DSB [A3] and not SSB [A3J]. 

Early in 1955, ASRE [Admiralty Signal and Radar Establishment- and afterwards ASWE {Admiralty Surface Weapons Establishment}] published the very first document on RATT in HM Ships which was called "ASRE NOTE 3/55".  This document introduced RATT into the Fleet and from that point onwards things changed for all in the RN Communications Branch [particularly for the telegraphists], those who would operate the new gear, and for all in the WE Branch [Weapons Electrical] who would maintain the equipment.  This latter task was not an easy one.  By and large the equipment was easy to use and maintain, but the early teleprinters were not, and many a young WE rating came close to a visit to Netley Hospital [on Southampton Waters] for therapy designed to stop people going insane. Additionally, the requirement to read both the RATT and the CW Broadcasts [each carrying the same traffic] put a demand on the stationery office, the confidential waste sack system [no shredders afloat in those days] and on the W/T office organisation.  Incidentally, the confidential waste sacks were stored and kept for return to harbour where they were burned in dedicated incinerators. 

The introduction of RATT into the Fleet, whilst purporting to cover what the Morse code systems were already covering, namely an incoming system from Shore [Area Broadcast], an outgoing system to Shore [Ship-Shore] and a system to talk to other ship [Inter-Ship Communications] really only fulfilled the Broadcast side.  The Broadcast side had the necessary space or frequency diversity arrangements [two or more aerials being used or two frequencies/frequency bands being used HF and LF, and two RATT channel processors], BUT, ships did not have the means to TRANSMIT RATT using FSK so could not communicate UNLESS they employed A2RATT and ONLY THEN on UHF. A2 is universally known as MCW [Modulated Carrier Wave] where a carrier is emitted with a single fixed tone of 1kHz in each of the sidebands Upper and Lower:  it therefore transmits three unique frequencies and the distant receiver does not require a BFO to demodulate the signal.  A2RATT is an emission using A3 [DSB] transmitter where the carrier is transmitted plus either a 'high' tone in each sideband or a 'low' tone in each sideband, again transmitting three unique frequencies at any one time period.  The 'high' and the 'low' tones represent the Mark and the Space of the RATT system. Thus, there was a provision for using UHF RATT for inter-ship working and also for ship-shore when the ship was close to or in a naval port but only on half-duplex; one station transmits and the other listens and then they swap over.  Morse code remained the order of the day for long/medium distance ship-shore working, and, when outside UHF range, CW and R/T were the normal method for inter-ship working. SSB and Satellites were still a 'million' miles away !

Until operators became familiar with RATT all signals were sent on the RATT Broadcast as well as on the CW Broadcast, and the receivers when used to receive RATT,  were not stable and therefore the RATT Broadcast operator had to keep adjusting the tuning when garbling corrupted the teletypewriter page copy: the phrase  "unattended reception" had not yet been coined.

Click HERE to read the short introduction to RATT.  You will note that we used TELETYPEWRITERS and not TELEPRINTERS

 The Broadcast system  was as shown in this overall block diagram

From this basic block you can see that the receivers [which you can see details of under RECEIVERS] are fed, in various combinations to the two RATT Converters A and B, which in turn pass out their signals to the middle unit, the Comparator: this is referred to as 'frequency diversity'.   The Comparator will pass the best of the two signals [A versus B] to a selection switch, but the operator also has the choice of selecting either Converter A or B based on experience, or in the case of only one receiver input, a specific Converter output only.  The teletypewriter is plugged into a plug and socket interface which is connected to the selection switch, thus bringing a good strong signal to the teletypewriter. The RATT Converter/Comparator is an American piece of kit called a AN {American Navy}/URA-8B and below you will see a picture of it. It became known as a CV89A, a reference to its oscilloscope {which engaged many an operators glancing look} when all valves generally began with the letters CV.

The RATT parameters used from the very beginning of RATT AT SEA, remained constant throughout the period covered by this website [to 1980] and were still the norm in RWA and RWC, RATT outfits we will meet later on this page.

Like the CW Broadcast, the new RATT Broadcast was parallel-keyed and transmitted as a multi-frequency circuit.  It had an LF element and several HF frequencies designed to ensure that the geographical area it was designed to cover had few {if any} nulls or silent zones, and that given the certainties/uncertainties of the ionosphere and enough LF transmitter power to ensure a good ground wave path, all ships should be able to read the Broadcast twenty four hours a day without the need to shift to an adjacent area Broadcast.

Irrespective of what the technique is called or how the system used produced its signal, the end product at the aerials/in the ether was the same, and in this and all cases yet to come, for the HF signal a 850 Hz shift was used and at LF, a 85  Hz shift. Each can be described by a simple drawing, the principle of which holds good in every subsequent case of RATT in the Royal Navy. Note, later on, a 50 Hz shift was developed for VLF.

First take the ASSIGNED FREQUENCY, assigned that is to the circuit in question on the frequency band in use of a multi-band transmission. In this example, the Broadcast will be transmitted simultaneously on LF, 4MHz band, 6MHz band, 8MHz band and on the 12MHz band, chopping and changing to suit day/night time propagation.  For our drawing we have chosen the 8MHz band and specifically the 8358kHz frequency which is the assigned frequency. To obey the International Rules laid down by the ITU and the CCIR, we must centre [as far as we are able] our signal around this frequency so that we cause the least amount of interference to adjacent assigned frequencies which may be in use by other users: the latitude given is generous, so that in truth, no interference of any kind should be caused. To this frequency we are going to ADD a RATT signal which consists of one AF tone when the teletypewriter keyboard is not in use, supplanted by a different AF tone when the teletypewriter keyboard is used.  It is that simple, and after all, when using the Morse code we have an identical situation {two conditions} viewed from the receiving end, that when the key is not being used the tone = zero and when used,  the tone = 1kHz or something in the AF range best suited to the telegraphist's ears. Staying with the Morse code, when the telegraphist is not sending a message, his key is 'idle' or better still 'inactive' and when he is, it is 'active.' This applies to the keyboard of a teletypewriter. These two words are quite adequate for all our needs because they are explicit and need no further explanation.  However, for international engineering purposes, these names [still extant to this very day] are called a MARK = INACTIVE or IDLE and a SPACE = ACTIVE.

Let's have a quick look back at the Morse code circuit using these new names. When the receiver is receiving a MARK [the telegraphists is NOT sending Morse] the receivers AGC decays and noise is heard in the earphones, but as soon as the telegraphist touches his key [a SPACE], the noise is replaced by [hopefully] a good strong Morse code note.  This is fine because the human being can adapt and make all the necessary adjustments to his receiver [gain control, AF tone note, minute offsets to clear atmospherics or local interference] and this, coupled to his wonderful and magic logarithmic human ear, makes him the master of his environment, give or take a few heavenly interruptions !

This is clearly not the same for a machine which either sees 'black' or 'white', and nothing in between. To make sure that this RATT machine does not lose interest and wanders off [so to speak] we must keep it focused and locked-on ready to receive our next touch of the keyboard. We do that by making sure that it ALWAYS has a good strong signal so that noise, albeit at a much reduced level,  doesn't allow the AGC to decay.  Thus, the signal in the ether is the either the MARK condition of the RATT signal, meaning that the distant operator is NOT typing on his teletypewriter keyboard [the keyboard is INACTIVE] or the SPACE [but never together] when the keyboard {or autohead transmitter} is in use. This means that a RATT Broadcast transmitter is permanently transmitting, and a RATT Broadcast receiver is permanently receiving.

So how are the MARKS and SPACES generated?  Well every key function of the teletypewriter keyboard has a unique series of pulsed  currents and each pulse within the series is converted to an AF tone, which as stated is either a MARK or a SPACE [2 conditions] so the combination range is 2 to the power 5 = 32 possible combinations.  Here is a list of the combinations as on the American teletypewriter in RATT 1.

Number of Signal Code Element Symbol US Teletypewriter Type 12
1 2 3 4 5
1       A - -
2     B ? ?
3     C : :
4       D $ Who are you
5         E 3 3
6     F ! %
7     G & @
8       H
9       I 8 8
10     J ' Bell
11   K ( (
12       L ) )
13     M . .
14       N , ,
15       O 9 9
16     P 0 0
17   Q 1 1
18       R 4 4
19       S BELL Not used
20         T 5 5
21     U 7 7
22   V ; =
23     W 2 2
24   X / /
25     Y 6 6
26       Z " +
27         Carriage Return
28         Line Feed
29 Letters
30   Figures
31         Space
32           Blank Not used on Type 12

Click HERE to see the ITA Code No2

The system uses a five unit code for the five pulses of the intelligence and if we were to take a real live situation, say the letters 'R' and 'Y'  we would see that the pulse train produces a combination of alternate Marks and Spaces. To test a circuit all we need to do is prepare a paper tape to be transmitted via an autohead.  The black dots on the table represent holes in the tape where the peckers of the autohead are allowed to rise and fall and they in turn are the MARKS.  Where the tape is not perforated the pecker is held down and a SPACE is transmitted. 'R' and 'Y' run together, viz, RYRYRYRYRYRYRYRYRY produce a series of SMSMS for the 'R' and MSMSM for the 'Y' and since we have shown nine of each letter we would expect to see nine of the blocks just shown. The same condition is achieved by allowing the autohead to run 'open' i.e., with no tape in the gate, but nothing is achieved because there is no intelligence in the resultant signals, just the well recognised noise of 'running open'.

Coming back to the 'machine' bit again, a teletypewriter, when receiving, has to be told when a symbol stops and where the new and next symbol starts, otherwise the synchrony would be lost and the teletypewriter would resort to constant garble. To do that, we need to add a START and a STOP signal to our transmission, and to differentiate between the two conditions, the START is equal to one unit and the STOP to one and a half units. When added to the units of intelligence, the 5 Unit Code we have just explained, the code becomes a 7 Start Stop Code, and although we don't see the START and STOP in a tangible forms, the equipment automatically adds them before transmitting the signal.

Now let us apply the MARK and the SPACE to that assigned frequency above of 8358 kHz with a 850Hz shift. We can show this in two ways. First as a transmitter whose output is controlled by two crystals each controlled by the state of the teletypewriter keyboard i.e., MARK or SPACE, 'not in use' or 'in use' respectively. We can dictate which of the tones represent the Highest or Lowest transmitted frequency and there are conventions that we in the navy obey and which we will cover later on. Suffice for the moment to establish the idea of tones and where they come from and then shifts in any order. Have a look at this drawing.


It is an over simplification but nevertheless, shows the theory of RATT. The teletypewriter has two conditions 'in use', and 'not in use'. Both cannot be extant at any one time, so,  if we assume that the keyboard is not in use, we can see that the MARK goes forward , activates the crystal 8358.425kHz which tunes the transmitter to that frequency and radiates 8358.425kHz on the aerial into the ether.  That condition exists until the keyboard is operated when a change to the 'in use' side occurs. The Space is radiated, and the transmitter is pulled down by the SHIFT, 850 Hz to radiate on a frequency of 8357.575kHz.  Over to the right of the drawing, you can see the assigned frequency relative to the two transmitted frequencies [Mark and Space].  Note that the intelligence [the signal] is equidistant either side of the assigned frequency and that it itself is not transmitted.  Note also that only one frequency is transmitted at a time, although at a speed of even 45 bauds [60wpm] the change over between the two is so rapid that it can be difficult to ascertain frequency shift especially when the shift is very small.  It would be rather cumbersome if we were to associate the Mark and the Space with the output frequencies of the transmitter which they of course dictate: in this case we might say that the Space, for example, equals 8357.575kHz [or whatever the crystal No for that frequency] but that would only hold good until the next frequency change.  Better that we establish values  for the tones which are extant under all conditions.  In the next example we can do that easily as follows.

We have achieved exactly the same as in drawing one above with respect to the transmitted frequencies, but this time we have given a value to the tones and added them, one at a time, to the suppressed carrier of an SSB transmitter.  Later on, we will see this become the norm for RATT in the Royal Navy, but sometimes with different tone AF values.  Note in this case that I have made the Space the highest transmitted frequency whereas in the first drawing it was the lowest frequency.  This is called ARRANGEMENT and we will meet it later on.

In this early fit of RATT which was called RATT ONE officially, the B40D Receiver was used for 850Hz shift at HF and the B41 for 85Hz shift at LF.  HF used the WIDE part of the Converter and LF the NARROW part. The B40D [there was an A, B and C model also] was specially adapted for WIDE RATT reception and had a built in FSK Wide on its System Switch. Having tuned to the zero beat of the transmission being received, the operator would switch to the FSK WIDE position [high or low by trial and error] and this would offer the two tones of Mark and Space centred on 2.55kHz {of 2975 and 2125 Hz} to the connected Converter on the AN/URA-8B. Each Converter had its own 'scope and the operator would finesse the B40D tuning until he saw the correct picture on the 'scope.

Picture A was the correct answer in association with pictures E and F. When the transmitter went to Mark picture F was correct and if he saw picture E instead, he used the system switch on the B40D switching from FSK WIDE High to FSK WIDE Low for a reversal: a reversal could also be made on the AN/URA-8B. Once up and running with a perfect page copy on the teletypewriter [known as ZBZ5] the operator kept the show on the road by using the "Osc Trim" on the B40D to fine tune the local oscillator.  Produced for your convenience are pictures of the two receivers details of which can be found on the Receiver Page.
 B41C.pdf and B40D.pdf. The B40D used the 1kHz bandwidth position [same as for normal CW reception] and the B41 used the 200Hz  position for the narrow shift of 85Hz.

The B41 had no modification nor needs them for it received LF at 85Hz shift {42.5Hz either side of the carrier}. For this it used its ordinary BFO control which catered for a 1kHz audio Morse code note with a high and low position to help with interference. The heterodyned output required was shut down by the bandwidth switch to 200 Hz allowing accurate tuning for zero beat and little room for accompanying interference.

The demodulated AF tones were converted in voltages/currents for the working of the teletypewriter printing head.

Now staying with RATT ONE we move onto the next part namely that of transmitting and receiving on UHF for Inter Ship Communications and for Ship-Shore working when in UHF range of a naval port. For this purpose the 691 transmitter and its associated receiver, the CUH were used. With the UHF TX/RX came the RATT equipment and we re-visit the photograph showing the whole RATT ONE bays by clicking HERE.  Here you can see a piece of equipment on the left hand side top shelf, the left hand teletypewriter and to its left, the autohead which would transmit the 5-Unit code paper tapes.

This picture shows two ships communicating on UHF RATT, with seemingly, one transmitting continuously leaving the other to receive. However, the normal modus operandi was a send/receive circuit based on half duplex when a transmission would finish with the prosign 'AR' if no further communication was required, of with the prosign 'K' inviting the receiving ship to transmit back.  Normally this special RATT fit was sited in the BWO [Bridge Wireless Office] and used to transmit and receive on any 691/CUH equipment in the ship via the conventional plugging at the Main KH CCX [Central Control Exchange]. It could, as the Jack Box AP142 shows, also be used from the MSO [Main Signals Office] or the LRR [Lower Receiving Room].

All that we have mentioned to date about the teletypewriter keyboard, its pulses and conversion into Marks and Spaces holds true for the Tactical side of RATT, except that the AF tone values will now be established and the emission will change dramatically. The Mark tone was fixed at 700Hz and the Space tone at 500Hz. But first let us meet the equipment which processed the RATT signal and was the Tactical equivalent of the AN/URA-8B.  This was also American Naval equipment called AN/SGC-1A.

It could be set to function as a transmit only [TX], a receiver only [STANDBY] or a transmit and receive circuit [AUTO]. It converted the Marks and Spaces from the teletypewriter into AF Tones before passing them on to and controlling the 691 transmitter, and AF Tones from the UHF receiver to voltage/current to drive the teletypewriter. You will have seen from the title of the picture above this one {UHF RATT SYSTEM} that the emission was called a "TWO TONE MODULATED UHF SIGNAL".  This required a DSB {A3} Amplitude Modulated system resulting in a relatively wide transmit bandwidth but mitigated by the UHF frequency of 277 to 283 MHz.  In any A2 RATT system there can be no 'Arrangement' because the Mark, for example, might be the highest tone/frequency in the upper sideband which will mean that it is the lowest frequency in the lower sideband.

In the very early 1960's their Lordships introduced a face-lift for RATT 1 which was the start of the RATT Transmission revolution. Its purpose was to add an extension to the original RATT fit at sea. It retained the normal RATT facilities and provided further facilities including HF FSK transmissions and HF simplex or duplex channel working.  Simultaneous reception and HF or UHF TWO TONE re-transmission of the HF Broadcast was included. Further minor facilities were available to most ships fitted with RATT.

Introduced with RATT 2 was the TELEPRINTER in lieu of the Teletypewriter and a distribution panel so that a teleprinter could be plugged into any one of six loop facilities providing a much needed versatility. Then came a new transmit/receive switch, and finally, RATT signals in the teleprinter/teletypewriter loop system, which we have just discussed in full, could be passed to the new Frequency Shift Keyer rather than to just the UHF equipment. The keyer was to simply act as an HF transmitter exciter which would shift the output frequency a small amount between two fixed frequencies in sympathy with the keyboard and autohead signals. In a way we have already dealt with this in our picture of a transmitter being controlled by two crystals each in their turn being switched on and off by either a Mark or a Space. If you have forgotten look at this BOOKMARK and to get back here to continue, click on the BOOKMARK at the bottom of the picture you are returning to see.

The new bays available with RATT 2 were:-

  • Standard RATT Bay [Basic arrangement -HF/LF Bay with Two Tone Bay adjacent]

  • Combined Broadcast and Two Tone Bay [one teleprinter only]

  • Broadcast Bay [HF/LF]

  • Two Tone Bay

  • HF/LF Broadcast Bay and Two Tone Bay in the same office but separated because of lack of space for one full unit.

This is what the 'new' RATT Bay looked like after the make over.

The typewriter and Morse key have been retained as a general purpose bay from where a Morse circuit could be operated always assuming that the FSK/MORSE switch on the Distribution Panel Teletypewriter is switched to Morse. The two receivers given over to that function have now gone leaving just the three [2x B40D and 1 x B41] for Broadcast, and a second autohead has been added, now one for each teletypewriter - note the promised Type 12 teleprinter is nowhere to be seen.  In the background at position 'C' is the new teleprinter/teletypewriter distribution box, and at position F1 and F2 the new send/receive switch for connecting either of the Broadcast Converters to other parts of the system for a re-radiation, if necessary, or for switching on the carrier of a transmitter ready to add modulation to it from these bays. When using the FSK Keyer from the RATT Bays, a Mark is radiated from the associated transmitter when the switch is to 'TX' and when switched to 'RX' the Space is radiated.  This is called "FREQUENCY SHIFT KEYED MORSE", the Mark frequency being used to send Morse proper and the Space frequency radiates when the key is not pressed. Any ship wishing to receive the Morse need only tune to the Mark frequency and then shut the receiver bandwidth down to the minimum commensurate with still hearing the signal. If you have read [and first I would suggest you do so] the many tens of files in the series 1900 to 1913, you will have read about the ARC transmitter [which came after the SPARK transmitter] which first did exactly the same, only in those days the Mark was called the BACK WAVE and the Space the FRONT WAVE.   The send/receiver switches are out of play if the FSK/Morse switch is set to Morse on the Distribution Panel Teletypewriter.  The Two Tone side remains as in RATT 1, and the FSK KEYER for transmitting HF FSK is sited alongside the HF transmitter to be used down in a TR [Transmitting Room] and this picture shows the plugging arrangement between the RATT Bays and the TR.

So, all in all, some quite major new control systems, but the jewel in the crown was the ability to transmit FSK on HF circuits.



showing a teletypewriter and auto head plugged up ready to use FSK Keyer No 1 [attached to HF transmitter No 1].  You should now be able to put things together. The current pulses coming from the teletypewriter and the autohead are routed to the FSK Keyer  by the FSK/Morse switch.  As we shall see, the FSK Keyer converts them into control signals in order that the transmitter sitting on a Mark can be pulled off frequency a little bit [850Hz] representing the SHIFT to emit a Space.  There are several combinations of double-ended jack plugs plugged into the sockets on this panel and for RATT and CW,  little is not available or possible on this PJF [Plug Jack Field].

We have seen how easy it was to receive HF/LF RATT on the AN/URA-8B and how easy it was to transmit RATT on UHF using the AN/SGC-1A, so let us now look at the HF FSK KEYER. This is the first one fitted, but very soon after fitting it was realised that spares and support for the American kit were running dangerously low so a re-think was in order. 

This was the KY-75/SRT, another American Navy piece of kit. Apart from the Type TCS receiver [see its scuttle on the receiver page] everything we had from the USN proved to be good kit with a high MTBF [Mean time between failures] and a better than average MTTR [Mean time to repair].  Just about every RN telegraphist who had joined the navy in the late 1930's and was still at it in the early 1950's had 'cut his teeth' on American W/T equipment.  We won't dwell on this piece of equipment, suffice to say that it was 'conventional conversion kit' and served as a transmitter exciter to generate Frequency Shift Keying [FSK].

In its place with lots of know spares and support came the FSK Keyer the GK185. This, like so many of our newly introduced kits, was British, and bit by bit in the 1950's, old British and old USA equipments were replaced with genuine pussers WD↑ equipments, chief of which were the 601 series of transmitters and the B40, B41 receivers.

This is the GK185A.

and it performed well almost leading the RN into the world of automation and away from the labour intensified Morse code world.

These are the block diagrams of both of the FSK KEYERS.

Looking only at the bottom block for the GK185A.  GK185A became synonymous [almost] with that lovely American transmitter the 89 which was finally buried after much use, in the shroud of the 89Q: however, the GK185A was also used to excite transmitters in the Type 601 series also.  The 89 above all other transmitter was the catalyst leading us from the blinkered and almost parochial world of Morse Code for the sparkers [telegraphists], and Radio Telephony [R/T] for all other users in the ship requiring the services of the W/T department, into the 'modern' world!  It served proudly in the RN in everything from submarines to carriers and saw much action throughout the whole five years of WW2. It is therefore worthy of a closer look: the parameters of the transmitter are mentioned over on the transmitter page.

 This is one the original handbooks  for what the Royal Navy called the Type 8M which the Americans called something entirely different but usually the MI-8167 Series : there were many models of this stop-gap transmitter brought over in the hundreds to help us fight the second world war. The typing of "Type 8M" above is not a mistake and many in the WE [Weapons Electrical] Branch always referred to the transmitter by this name. It became known {to all in the Service} as the Type 89 but the basic {as shipped} model was soon modified for R.N., use.  This little group of pictures starts with the basic model, and then shows the Type 8M in "RN Colours"; the 89M [first modification], the 89P [second modification] and the 89Q [third modification] and all these modifications are major,  necessitating the issuing of new drawings/handbooks and stores/establishment lists known as 'E Lists'.

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89 89 [as shipped]
modified for RN use.
89M 89P 89Q

You will see that the evolution of the set adds more and more dials and tuning knobs as it progresses, but it is the evolution of frequency determination which is of the greatest importance. The basic 89 had a stable and accurate output, but it was totally controlled by crystals, so if you didn't have the correct crystal you couldn't set watch on a circuit and that was hardly conducive to a flexible COMPLAN [Communications Plan].  That limitation was not corrected in the first RN issued sets.  The 89M added a VFO [Variable Frequency Oscillator] in addition to the XO [Crystal Oscillator],  but to cover the full frequency range of the VFO, three plug-in coils were required plugged in one at a time to cover the ranges 1500-4400 kHz, 4400-9500 kHz and 9500-20000 kHz. The 89P was a "stepping-stone" arrangement whereby frequency determination was offered as a crystal only version [like the 89 itself] or, by undoing a few screws and replacing a face-plate with a push-in device, it could be turned into a VFO only,  but delivering a more sophisticated system than was apparent in the 89M.  The Type 89P was ideal for facilities requiring only a few staid frequencies, like shore stations for example, but for ships and submarines {look at this picture},

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the face-plate was removed, the 'modern' VFO unit was installed on a permanent basis, and from that IDEA  the 89Q was born. However, this picture below shows what the designers of the set, the Americans, had in mind for the Type 89P which was accepted and fitted, but the British wanted to do away with the face-plate completely and to fill the hole, with an 'ultra modern' VFO and XO combined in order to get 'on tap' the necessary flexibility required in a warship. So the British came up with Oscillator Unit shown in the picture of the 89Q above - please return there now and note that from top left clockwise, it has a hole [double pin] to receive an 'L' type crystal; a meter; a rotary VFO dial and a range switch for the output frequency unlike what you see below which is two dials, two switches and a meter.

Whilst it is not recorded as such, we can safely say that with the British Oscillator Unit installed we had the Mk1 89Q, although why it wasn't considered a modification which would elevate the equipment to a 89R [or the next letter for a modification] is unsure: perhaps it wasn't considered a major modification!

For our purposes, MkII 89Q was a further modification to the Oscillator Unit.  This would allow entry to the GK185A FSK KEYER so that the 89Q could enter the 'modern' world of RATT. This was a simple modification and involved the fitting of a socket on the front of the unit. This is a picture of it with the socket immediately above the meter and just lower over to the left, a switch marked 'NORMAL' and 'FSK'.


 The drawing below shows the basic schematic of the circuit after the MKII modification had been carried out.

You have just seen the pictures of the British Oscillator Unit and that same Unit modified for FSK working.  Here, in this drawing,  you can see them in schematic form. The crystal holder is at the bottom left of the picture [a device sandwiched between two north/south facing brackets]; the meter is marked 'A' in a circle to the bottom right; the switch is S501 {off plus positions 1,2 and 3} and the tuning dial is C503, a variable capacitor. Now for the FSK modification. Returning to the area of the crystal holder [bottom left], look for the NEW switch S502 with two positions, namely 'N' for Normal, and FSK. Below it is a fixed capacitor C510 and then SK1 [socket one]. That is it. When switch S502 is set to FSK and the GK185A is physically plugged into Socket 1, the transmitter is ready to OBEY the signals of the FSK KEYER. It is academic but I will mention it anyway, the FSK KEYER is connected to the grid of the main oscillator valve V501, which in the Normal operating position, the crystal is connected to the anode of the valve. As we will see the crystal now used for FSK is housed in the GK185A.

This little drawing shows how the GK185A produced its FSK signal. This time we are going to radiate on an assigned frequency of 8358 kHz on HF RATT Ship-Shore using the standard 850 Hz shift. Now, just a couple of things we have to take into account using the 89Q. When using frequencies of 1.5 to 6.7 MHz the output is the same of the crystal used; 6.7 to 13.4 MHz the transmitter doubles so we have to halve the value of the crystal, and from 13.4 to 20 MHz it triples so the crystal value = one third that of the final output frequency. Also, if we choose a frequency which is going to be doubled, it will also double our SHIFT from 850Hz to 1700Hz, so we have to set on the GK185A [for 8358 kHz] a shift of 425Hz only. Complicated? Well a trifle but follow me and I will make it easy !

The GK185A has 8 operational crystals 6 of which can be removed and changed for different transmitter output frequencies, meaning that at any one time, without having to reload the GK185A, we can transmit on up to six unique frequencies only using virtually any shift right up to 1000Hz.  Here is the drawing we will use for FSK RATT 850 Hz shift on 8358 kHz.    The text in Lines 'B' and 'D' below assumes a normal 850Hz shift at a frequency below 6.7 MHz when the Transmitter Type 89Q does not double the frequency or the shift.    The text to the right of the drawing is fully relevant to this case for a frequency of above 6.7 MHz.                                                 
Out of 'B' comes 4500 kHz Mark and 4499.575 kHz = Space, 850 Hz 2 = 425 Hz below it. Out of 'C' 5000 kHz. 'D' throws out many frequencies and 'E' filters for the range 500 to 501 kHz. When 4500 kHz mixes with 5000 kHz it produces 500 kHz and when 4499.575 kHz  mixes it produces 500.425 kHz [inside the range of up to 501 kHz]. 'F' has this input plus the input from the selected circuit frequency crystal. Since we are already playing with a 500 kHz MARK, we have to reduce the value of the crystal chosen by 500 kHz AND to take account of the Type 89Q transmitter doubling whatever frequency we give it from the GK185A, AND that our transmitted signal must be equidistant either side of the assigned frequency.   Therefore, the chosen crystal frequency is 8357.575 2 = 4178.7875 - 500 = 3678.7875 kHz {highly unlikely but never mind}.  So into 'F' we have a range of frequencies from 500 to 501 kHz and 3678.7875 kHz from a crystal. Out of 'F' comes many permutations but the Upper Side Band [USB] frequencies are selected by default and then amplified in 'G' before being passed as a 2 Watt signal to 'H' the 89Q transmitter. When the Mark is present @ 500 kHz 'F' gives out 4178.7875 kHz and when the Space is present @ 500.425 kHz the output frequency is 4179.2125 kHz.  The Type 89Q transmitter DOUBLES these frequencies and amplifies from 2 Watts up to 300-400 Watts [thereabouts] emitting an 850Hz shift with a centre frequency of 8358 kHz.  Was Morse Code working easier ?

The procedure for operating FSK with the Type 601 Series was exactly the same, but see RATT 2A below for further details . 

With RATT 2 came the ability to transmit TWO TONE RATT on both UHF and HF simultaneously through a KH device called a Design 11, which for all practical purposes was a parallel-keyer. Why anyone would want to generate A2RATT on HF I don't know especially when HF FSK was also fitted.  It is now and was then, a terribly inefficient system wasting power transmitting a full carrier and an unnecessary sideband!

The weak-link for RATT 2, and for many years to come was the Creed Type 12 teleprinter which was, plain and simple, a disaster. It didn't function properly when the Fleet was operating on 45 Bauds, and when 50 or 75 Bauds were ordered, the damn things shook to pieces, literally.  This is a picture of one of these horrors.

Using the new Distribution Panel Teleprinter fitted with RATT 2 many radio relays could be achieved and in this file I have just shown a few. RATT2 PLUGGING.pdf

Towards the end of the RATT 2 period, the expression FSK became unfashionable and in its place came FST [Frequency Shift Telegraphy]. This led on to FST being officially called "F1" and all circuits thereafter were described thus.

On this same theme, was the 5ABA for the Type 601 series, and a little later on, into what became known as the RATT 2A days came the GK198 and GK199, respectively for the 601 series and the 640, to made them compatible with a brand new system called RWA. More of all that in a moment. Before then let us look at

RATT 2A was really a small add-on to RATT 2 and was ship-significant rather than pan-navy-significant. Transmitters like the 89Q were rapidly coming to the end of their lives,  and the 'writing was on the wall' for the services offered by the 601 series: Click HERE to see a file about the 601 series and its use for RATT.  For my money, some member of the MOD procurement division, even though he might not have known how clever his initiative was, brokered an agreement with Marconi and bought lots and lots of their transmitter NT204 which we called the Type 640.  It was a very fine piece of equipment.  The 640 started its fitting programme before RATT 2 was 'put to bed' and by now the requirement to transmit FSK at HF [FST/F1] had become the accepted [and expected] norm.  The Keyers they already had where carrier shift keyers, but for an SSB transmitter, what was required was a tone or sub carrier shift keyer.  That package was delivered as the Outfit GAA and again, ready made off-the-shelf from Marconi.  They didn't buy too many of these units because as soon as the RWA RATT equipment was made available {see Part Two} the GAA was made redundant. This is it and note the similarity between it and the frequency standard FSB - it is even in the same metal box.

It did exactly what the GK185A had done, namely to put an 850 Hz shift RATT frequency into the ether;  however it did it slightly differently.

This unit, in conjunction with the RATT 2 transmit/receive switch fitted in the RATT Bays [and a couple of other switches] controlled the 640 transmitter through the KH CCX system, by opening up the microphone lines [pressel switch] and allowing the Tones the GAA produced from the teleprinter keying source input to enter and add to the sub-carrier with the transmitter in the SSB USB Suppressed Carrier Mode {A3J}.  The tones used were the proverbial 2975Hz and 2125Hz necessitating a transmitter dial setting of 2.55 kHz below the assigned frequency. Remember this drawing ?

Good, then I will say no more ! Note that in this drawing the SPACE frequency is the higher of the two radiated frequencies. In the RN we call this ARRANGEMENT 1 and of course it is most important that the receiving station keeps this arrangement, although the value of the tones he uses at his end after demodulation is his own business.  We signal our emission by stating "F1/850/1/8996" where F1 =Frequency Shift Telegraphy; 850 the shift - the distance between the Mark and Space tones; 1 = arrangement and the assigned frequency.  Providing he understands that it is a 850Hz shift and Arrangement 1, his terminal equipment will dictate the offset he uses on his receiver to achieve the tones required. Offset is a phrase meaning the distance between the dialled on frequency on the transmitter or receivers synthesiser and the assigned frequency given in the COMPLAN. The GAA had a limitation in that it could only be used in Arrangement 2 where the Mark signal is the higher of the two frequencies.  Thus to meet the requirement of the COMPLAN to use Arrangement 1, such a ship would need to offset 2.55 kHz UP  [dial set above the assigned frequency] and then use the LSB all of which would reverse the arrangement.

With but a few and minor enhancements the navy waited with bated breath for the next revolution which was to be across the board encompassing control systems, frequency standards, RATT reception, RATT transmission, receivers, transmitters, aerials, on-line crytography, etc etc, leading on into satellites.  They were exciting times for us men reared on hard work as Morse Code telegraphists.

We take a break now and prepare ourselves for RWA which is mentioned in great detail in Part Two.