Radar type 284

[kasperhogh]

Hi
I'm writing a big assignment about radars now and back in the battle between Bismarck and Hood.

So I have decided to look further on too the Type 284 radar, which Suffolk used to spot Bismarck in the Denmark strait.

My problem is now, since I write in physics I have to know how the old radar works compared to the ones today
So I really hope someone can link me to some sources where I can read about how the Type 284 radar works.

Thank you in advance, and sorry English is not my first language.

[Bgile]

If you look at some of Dave Saxton's posts there is a lot of info in there.

[kasperhogh]

Thank you, I have looked at some of his posts, but the problem is I need sources I can refer to in the assignment.

[Keith Enge]

The best book that I know on the subject is Norman Friedman's book called "Naval Radar". It is especially useful in that it is divided into two parts. The first part is theory. A list of the chapter headings gives some indication of its breadth of discussion. They are:

The basis of radar systems
Radar signals
Factors in radar performance
Displays and antennas
Radar functions
Integrated fleet systems
Radar development
Radio
Electronic warfare

The second section is a catalog of all of the radar sets of the various navies from the first until the book's publication in 1981. The discussion of Type 284 includes the following. The antenna had two 21 foot troughs, each with 24 dipoles (dipoles so one could transmit and the other receive). In its initial versions, it didn't have a particularly great amount of power but that was increased in later versions. It was claimed to be accurate to within 200 yards in range. However, the beam was eight degrees wide (later reduced to five). In either case, therefore, the beam was too wide for bearings accurate enough for gunfire. Therefore, bearings for gunfire would have to be obtained some other way, visually or with a different radar.

I Iooked for the book at amazon.com but, although available used, it is very expensive. However, there seems to be a downloadable electronic version at various ebook sites.

I hope this helps, Keith

[kasperhogh]

You are my hero Keith. It was exactly was I was looking for, and it's available at my library. So I'll go pick it up right now. Once again thank you for all your help.

[dunmunro]

I would suggest reading this file:

http://www.rnmuseumradarandcommunicatio ... RT%20B.pdf
Excellent data on the Type 284 and the sinking of Scharnhorst and some about Bismarck.

and looking here:
http://www.rnmuseumradarandcommunicatio ... E%2019.htm

You should try and read RADAR At SEA, by Derek Howse

and

The applications of radar and other electronic systems in the Royal Navy in World War 2

[kasperhogh]

Thank you, especially the fist link is very helpful, can you tell me what book it's scanned from?

[dunmunro]

Thank you, especially the fist link is very helpful, can you tell me what book it's scanned from?

Apparently it is chapter 12, Part B, from an unpublished internal RN history of the Admiralty Surface Weapons Establishment:

No organisation can tell 'our' story better than our own Scientists who worked for ASWE [Admiralty Surface Weapons Establishment] and of course many other places of excellence. Their story is not in the public domain, although one astute man by the name of O.L. RATSEY did bother to get his pen out to leave for posterity a 'wonderful' composition which he called "AS WE WERE", the AS WE representing ASWE. "AS WE WERE" had a title which read "Fifty Years of ASWE History 1896-1946", and it has a Section on Radar fully relevant to our needs. The composition was copied many times and issued in an A4, blue coloured, hard-back cover, with punched pages held in place by a four-ganged spring clip. Regrettably, the copying of this composition was so prolific that many copies, including ours, is often difficult to read, and sometimes needs to be re-processed before being re-produced. The modern computer technique of OCR [optical character recognition] is also out of the question because of the poor quality offered to the associated scanning device.

http://www.rnmuseumradarandcommunicatio ... E%2019.htm

[Dave Saxton]

The genesis of the 284 began in mid 1939 when the Admiralty fired almost everybody responsible for radar R&D at the ASE (Admiralty Signals Establishment). Progress from 1937 had been nill. A young self taught engineer F Coales attached to the ASE was placed in charge of the 60cm project. The Admiralty had planned on three radars being developed; of 4 meters wavelength, 150 cm wavelength, and 60cm wavelength. The 60cm project was to be specific for gunlaying. Coales turned to the private firm of GEC and basically subcontracted GEC's scientists and engineers- guided by Coales himself. Coales later said of himself he had a vision but does not "read math". He demanded that the GEC people put everything in laymens terms. The design GEC came up with was the basis of all the 50cm gunlaying radars, the wave length having been changed from 60cm.

Actually the wave length was 51.5 cm. The basic 50cm design was used for the 283, and 285 radars as well. These other designs were for the flak batteries and differed in their antenna designs. The 284 radar consisted of one of two possible antenna designs mounted to the fire control directors. This consisted of the one already alluded to, known as the "Pig Trough", which consisted of individual 1/2 wave dipoles arrayed end to end within a three sided box reflector to eliminate any back leakage. The other possible antenna was the Fishbones usually associated with the Type 285 flak and secondary battery radar. The Fishbones was two Yagi antennas, which resemble VHF TV antennas which used to be ontop of houses all over- if your old enough.

(the following is for the early model 284)The transmitter was a push pull amplifier consisting of two GEC Micro-Pup transmitter triodes. Power output was about 25kw at the transmitter but about 12kw from the antenna (British power output was measured at the transmitter instead of at the antenna per German and US practice). The receiver was a unique super het design in that it used anode modulated mixer Pentodes (a type of vacuum tube). Usually, with vacuum tubes the signal is applied to the grids, but in this case GEC tied the grids to ground. This minimized inherent noises of pentodes and made for an acceptable signal to noise ratio at 600mhz (50cm) while simultaeously having a large bandwidth mismatch. Because of the unique anode modulation of the receiver and the transmitter tubes the 50cm radars required extended warmup times of up to 45 minutes before they could be used. They also required being shut down and rested after a few hours of constant operation.

Instrumentation was by a single A-scope only and therefore completely abstract. The A-scope measured only range with the pulse ocurring at the zero point along a linear time base. The echo pulse return was a deflection or kink in the trace which occured at the appropraiate place along the time base. By converting the comparitive distance between the zero point and the "pip" on the time base to range; range to target was measured. Range accuracy was nominally 240 yards.

The resolution for range was 300 meters because of the 2 micro sencond pulse width.

The bearing which the antenna was aimed to could be determined to a finer degree of accuracy by determining at what bearing the signal provided the greatest pip amplitude. This method was known as max signal, and was accurate to 3/4 of a degree.

In tests of the first production 284 installed on the battleship King George V in Dec 1940 set the reliable ranges as follows:
14,00 yards to a destroyer
20,000 yards to a cruiser

It was not tested to another battleship, but the Suffolk's 284 was able to detect and track the Bismarck to a max range 26,000 yards. KGV's 284 first detected Bismarck at about 25,000 yards.

[Dave Saxton]

Type 284M:

By 1942 an improved 284 was made available and installed on new contruction warships. Those warships which already had a 284, or in some cases any radar at all, had to wait until production caught up and so the unimproved early 284 continued in service through into 1943 in some cases. The improved 284 prototype was initially designated Type 284I, but was known as Type 284M when installed on warships. Among the improvements were:

*Increasing transmitter power to 120kw.
* Utilizing a common mode antenna
*Introduction of Beam or Lobe Switching.
*Decreasing the pulse width to 1 micro second.

This produced the following performance improvements:

Range was increased to 29,000 yards to a battleship. It may seem that such a huge increase in power, along with a 4 fold increase in antenna gain, would result in larger range increase, but it requires a 16 fold increase in power to double the range all things being equal. The bandwidth of the receiver was also increased to 4mhz to develop a sharper leading edge of the pulses (they used a flip flop circuit from the receiver to trigger the pulsers which delivered a high voltage pulse to the anodes of the transmitter triodes) to improve range accuracy along with a decrease in pusle width to improve range resolution. Both these revisions reduced range by themselves. Bandwidth should be the inverse of pulse width to gain the lowest signal to noise ratio required for detection, and the illumination energy is radiated power X pulse width. It was also observed that lobe switching reduced the range by about 15%.

The common mode antenna delivered a horizontal beam width of 4.5 * according to the ASE Operators Manual. Other sources indicate 3*.

Lobe Switching utilizes two beams switched alternately: one aimed slightly left and the other slightly right of the target, to determine direction more accurately. If the amplitudes from the two beams match then the antenna is aimed directly at the selected target. The 284M utilized a geneva mechanism to provide intrumentation of the lobe switching on the single A-scope. If the two signals amplitudes matched; the trace on the A-scope held steady, but if it was off line slightly, the trace would begin to flicker. Bearing accuracy with this method could be as good as 0.08*.

The range accuracy using a paper correctional template to compensate for distortion on the CRT is listed as 120 yards for the 284M in primary documents.

Decreasing the pulse width effectively improved the range resolution from 300 meters to 150 meters.