四式空六号無線電信機三型 Shi-shiki kū-roku gō musen denshinki San-gata, Type 4 Ku 6 wireless telegraph Model 3). The FM-1 was an Air to Surface radar developed for small aircraft by Tokyo Shibaura Denki in 1944. Only one prototype was constructed and tested September 1944. The radar was with 70 kg lighter then the 110 kg weighting H-6, but it’s performance was the same. The type was deemed unpractical for use and was cancelled in favour of the FM-3.

Reports of the U.S. Naval Technical Mission to Japan

Technical specifications

四式空六号無線電信機三型 / Type 4 Ku 6 wireless telegraph Model 3
Designation FM-1
Object Patrol and Search
Research started February 1944
Finished September 1944
Operational status Development cancelled
Installation Small Aircraft
Observer’s Seat
Frequency 2 meter / 150 kHz
Power Output (Peak) 4.2 kw
Pulse Length 15 µs
Repetition Frequency 250c/s
Weight 70 kg
Units build 1 experimental prototype
Transmitter Oscillation Circuit   Modulated Oscillator  
  Oscillator Valve U-319 x2
Receiver Intermed. Freq. 10 mc
Detector 1st UN-95A 2nd SORA
Local oscillator UN-955
Scope
Representation
Diameter 120 mm
Scanning Axis Linear
Scale Sinusoidal
Antenna Type Head: Yagi Sides: Folded Doublet
Gain 16db 6.5db
Beam Angle Horiz. θƒ = 30° θƒ = 28°
Vertical θƒ = 35° θƒ = 30°
Max. Range (Max.Effective Scale) 250 km theoretical
90-110 km against large ships such as aircraft carriers
70 km agains aircraft
Minimum Distance 5 km at 1000 m
Accuracy of Range ≃± 5%
Distance Discrimination 4 km
Accuracy of Bearing ± 3°
Angle Discrimination ≃ 60°
No. Of Operators Observer

Sources

Reports of the U.S. Naval Technical Mission to Japan, 1945-1946. Series E-02 Japanese Airborne Radar

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