Postby Dave Saxton » Tue Apr 22, 2008 5:27 am
CXAM, SC and SKThese are all based on the same basic 1.5 meter wave length radar system design. These radars were built by RCA based on a prototype developed by the Naval Research Lab called the XAF. The XAF was first tested in early 1939, and the Navy was jazzed that it could track shells in flight and spot the fall of shot. Max range at that time was 16,000 yards. CXAM was the first production version, with the first sets going on Pacific Fleet carriers during 1941. It proved valuable during the early carrier battles, and was a major player. The SC utilized a small antenna so it could be mounted on small warships. Of course the use of a small antenna caused it to have poor bearing resolution. The SC was nonetheless used though out the war. The SK used a large antenna array of either a mattress dipole array (the flying bed spring) or a large round dish. The larger antennas and their greater gain produced a significant boost in range compared to the SC. The SC could detect a battleship to 37,800 yards, and the SK extended this to about 50,000 yards. The SK used a PPI display instead of an A-scope. The SK became the main air warning radar for the USN during WWII. Performance figures from USN sources are: bearing resolution 10*, range resolution 500 yards. I’m hesitant to list the range accuracy, because it’s seems way out of line at +/- 1,000 yards.
SG The SG, built by Raytheon, is often described as the most important naval radar of WWII. This is probably a correct assessment at least for the crucial Guadalcanal battles . The SG was a better utilization of the 10 cm wave length technology given by the British, than the Royal Navy’s own Type 271, in large part because it used a PPI display from the start. This is the kind of display we see in the movies. The PPI was much easier to read than the abstract display of an A-scope. If one could read a map, one could make sense of the PPI display. A mistake of the first versions of the SG, was that the one PPI was in the radar office and could not be viewed by the ship’s command on the bridge, or in a CIC (A mistake the Germans did not make with their Berlin radar systems). A PPI is not as accurate as an A-scope, but the SG was adequately accurate even with the PPI. Range accuracy was +/- 150 yards. The resolution for range was 500 yards (300 yards on the A-scope). The antenna, although small, could deliver a beam width of 5 degrees with a 10cm wave length. Average range was about 40,000 yards. The SG could detect a surfaced sub at 12,000 yards, and a periscope to 4,000 yards. The antenna was a reflective type shaped like a small curved blade, and was small enough that it could be mounted just about anywhere convenient, including the mast head of small warship.
In mid 1943 the SG-I came into service. This version had multiple slave PPI displays, and the power output was boosted to 50kw. I try to avoid placing much emphasis on power output, because by itself it’s meaningless. For power output to be meaningful it must be correlated with other factors, such as wave length, band width, min signal to noise ratio, antenna gain, noise temperature, and so forth.
I’ll try and provide some information on the SJ and SD, and perhaps the French radar research when I find some time.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.