Radar No4 Mk1

Radar, AA, No4 Mk1

Purpose

Mobile equipment for early warning of aircraft to indicate the approximate range and bearing to equipment radar AA No3 Mk1.

History

Description

Four-wheeled trailer with steel and wooden cabin for Tx and Rx. Rotatable aerial array mounted on steel frame-work, collapsible for travelling. Known as the ZPI (Zone Position Indicator) part of the Canadian GLIII(C) System.
The APF was the No3 Mk1.

Presentation Unit

Range & Bearing : PPI type (in APF cabin, see Radar, AA, No3 Mk1)
22 rpm radial sweep.

Physical data

Length	20' operational
	20'9" travelling
Width	7'8" operational
	7'8" travelling
Height	25'6" operational
	10'8" travelling
Weight	6.45tons
Wheelbase	10'4"
Turning circle	30'0"
Ground clearance	12"
Wading depth	2'3" still water
Bridge class	4/6
Towing vehicle	Lorry, 4ton, FWD

Electrical data

Operational wavelength	145-155 Mc/s
I.F. freq	31Mc/s
Receiver bandwidth	1Mc/s at -3dB
Tx power output	120 kW
Tx pulse width	2/4/6 us
Recurrence freq	800 to 1200 c/s
Detection accuracy	range +/- 1000yds
	azimuth +/- 2deg
Detection range	50,000yds
Data Transmission	by magslips

Antenna System

Common T and R.
Horizontal 7-element co-linear array and parasitic reflectors with vertical 6-element array intersparsed.
Open wire feeders.
Turning gear : Aerial array rotated at 22rpm by 3/4 h.p. single phase motor.

Power Supplies

115V/230V ac 50c/s or 60c/s, single phase.
Normally supplied by a Cumminss diesel 31 kVA generator.

Operators

Technical : 1
PPI operator : 1

I.F.F.

Not yet fitted (1944)

Remarks

Careful siting required for long range and freedom from ground echoes.
Receiver IF signals fed to PPI unit in APF cabin by concentric cable.

References and Sources

Nomenclature : AA No4 Mk1 (ZPI of GL MkIIIC), 1944.
R.E.M.E. Museum Archives, Arborfield.
No1 CRLU Radar History
Clive Prothero-Brooks, RCA Museum, Shilo, Manitoba, CA

More No4 Mk1 pictures

Production model ZPI trailer showing elliptically polarized antenna. Early model ZPI in the background.

No4 Mk1 radar getting ready for shipment

Ten No4 Mk1 radar trailers getting ready for shipment

No4 Mk1 radar residing at the Royal canadian Artillery Museum, Shilo, Canada.

No4 Mk1 residing at the Royal canadian Artillery Museum, Shilo, Canada.