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Yamato's radars

Posted: Sat Sep 20, 2008 4:00 pm
by Dave Saxton
The Yamato was equiped with three different types of radar. None of these radars were firecontrol specific designs. A 10cm fire control design known as the Mk3Model2, developed from the Mk2Model2, never made it into operation before the end. These were the active radars installed:

Mk1Model3 This was a long range Air Early Warning design. It operated on 2 meters wave length with pulse widths of up to 10 micro seconds, and a power of 10kw. The Antenna was a dipole array hung off the tripod main mast aft of the funnel.

Mk2Model1 This was a general tactical radar used for both surface surveilance and air warning and operated on a wave length of 1.5 meters.These sets used the antennas mounted to the arms of the main 15 meter rangefinder apparatus. Musashi had one set of the Mk2Mod1 as early as mid 1942. During test shoots off Katsura Island in Sept 1942 the radar was always knocked out by the concussion of the 18" salvoes, that sent complaints to the Naval Technical Research Lab for a remedy. The radar was upgraded at least three times with power reaching 13kw in the later models. The range resolution was 450 meters. The range often listed is only 20km, but that may not be correct at least for a large target radar cross section such as a BB or a CV. In 1944, there were actually two sets of the Mk2Model1 installed with the antennas for each radar installed on the left hand and right hand arms of the main range finder. This is most interesting because it could have allowed a precise fix of an isolated target's bearing by maximizing the signals from the left and right hand radar sets. The horizontal beam width was wide however.

Mk2Model2 This was a centimetric radar operating on a wave length of 10cm. It was a general tactical, sea surveilance, and air warning set. This radar was first made operational in the summer of 1942. The transmitter was a cavity magnetron producing 2-5kw of power. The antenna wave guide windows were small round horns (looking much like fog horns), one for transmission and one for receive. The Yamato had two sets installed with the antennas installed on platforms extending from the left and right sides of the tower bridge structure. These horns are so small that they can't be easily seen in photos, or if noticed at all are often mistaken for fog horns or loud speakers. Brown says that it probably compared well to the early model British 10cm Type 271 radars without PPI. The range attainment listed in the literature vary widely from only 20km for a detecting a BB, to 34, 34.5, and 35 km for large surface ships. The 35km figure is plausable even with the low power and small antennas, if it used long pulse widths, as reported in some circles. Long pulse widths increase the illumination energy because the energy is the power multiplied by the pulse width, and because long pulse widths require much less band width at the reciever, essentially making the reciever much more sensitive. Since this was a general tactical radar fine precision wasn't required of it.

Re: Yamato's radars

Posted: Mon Sep 29, 2008 8:26 am
by RF
Is there any account of whether this radar was of much use on the Yamato's last mission?

Re: Yamato's radars

Posted: Mon Sep 29, 2008 1:54 pm
by Dave Saxton
Some US interviews of survivers revealed that they began plotting formations of air intruders from 70km. These radars could not provide effective radar control for the flak batteries.

Re: Yamato's radars

Posted: Fri Oct 03, 2008 9:50 am
by RF
Looking at that situation, given the weight of the air attack it presumably would be likely that if these radars could be used for fire direction they would not have made much difference anyway.

Re: Yamato's radars

Posted: Tue Dec 17, 2013 4:11 pm
by Dave Saxton
Follow up with new data:There was a write up by Rad Lab engineer Roger Wilkinson in 1946 on Japanese radars in the AIEE Journal.

Wilkinson reports that the Japanese designation system was so complex that Japanese themselves could not even keep it straight. The Mk2MOd2 radar was simply refered to as the 22 or Type 22. There were two improved Type 22 radars being developed at the end of the war. There was the Type 220 which was an improved 22 for surface search and an improved Type 32 for firecontrol. The range had been increased from 25km to 35 km. The Type 32 was like the Type 22 but it had two receiving horns instead of one, while retaining the single transmitting horn. The two horns were for conventional Lobe Switching. The lobe switching in this case provided a bearing accuracy of 0.5*, well inferior to Anglo American and German standards.

Wilkinson's data for Type 22 are:

Wavelength 9.2-9.8cm.

Transmitter was a water cooled M-312 Cavity Magnetron producing an max output of 6kw (the Japanese did not discover strapping). A 11,000 volt pulse was delivered to the cathode of the magnetron by a pulser.

The receiver was superhet with a crystal mixing diode and an M60-S split anode magnetron for local oscillator. The IF was 14.5mhz.

There were three A-scope indicators. One was the bearing indicator for maximizing signal or in the case of type 32 for matching the pips of the split beams on receive. There was a coarse range display with the time base in 5km increments extending out to 60km. There was a fine range display with range gates of 1,000 meters. It was very similar to the Precision Ranging Panals used on British radar sets of the period. The pip was moved so that the leading edge of the pip lined up with a line across the middle of the scope by a hand crank. The range accuracy on all models was 100 meters at all ranges to target.

The transmitted beam width was 15*. On the Type 32 each received beam width was 6*.

The pulse width was 10 micro seconds. :shock: This helped it to obtain BB to BB ranges of up to 35km with 6kw of power or 25km with 2.5kw of power of the earlier models. The submarine mounted version could obtain a range of 10km to a battleship from a surfaced submarine. The long pulse width resulted in an illumination energy of 60kw or 25kw. Another aspect of the long pulse width was no need for high band width, which increases receiver sensitivity. The long pulse width would have resulted in a range resolution of 1500 meters if conventional methods were being used.

Wilkinson reports that a Type 22 was set up overlooking Tokyo Bay for the US Army. They were amazed at how fine the diffinition was. How did the Japanese pull this off with a ten micro second pulse width?