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from the ground station to the aircraft, is also at present the subject of theoretical 
enquiry based on the work of Bremmer'* and Norton". 
5.17. Air Survey Equipment. The mobile ground stations already described are 
specifically designed and widely used for operations in isolated sites and undeveloped 
country. The equipment breaks down into sections for stowage in aircraft or small 
boats. The single radio mechanic required for each station does not have to perform 
any operation of a continuous character (e.g. pointer-following). While in practice 
each station generally has a crew of two, sometimes comprising a mechanic and a 
native cook, the operation and routine maintenance of each station is well within 
the capacity of one man. It is perhaps worth recalling that in the early days of 
Decca's use as a survey aid the system was criticised on the grounds that the station 
equipment was very heavy compared with secondary-radar systems then being 
operated for air survey purposes by the Services; while this was undoubtedly true 
of the actual *boxes', the Service-operated stations involved a far greater logistical 
load by virtue of the contingent of men deemed necessary for their operation and 
maintenance. 
5.18. In the survey aircraft, the installation is closely similar to the standard 
Decca navigational equipment'®, a typical receiver together with two pairs of 
Decometers weighing 65 Ib. The weight of the Mark 01 Flight Log and its computer 
and control boxes brings the total aircraft installation weight, less cabling, to 125 Ib. 
(57 kg.). The installation of a second pair of Decometers in an ‘automatic observer’ 
is straightforward and the direct numerical display of the information is useful in 
this connection. 
6. FUTURE DEVELOPMENTS 
6.1. The lines which future developments of the Decca Navigator system as an 
aid to air survey may be expected to follow fall under two headings: refinements 
and improvements in the instrumentation, and methods of correcting or eliminating 
errors associated with wave propagation. So far as the former is concerned, Decca 
receivers and ground stations have proved outstandingly reliable and it remains 
only to reduce some of the minor problems that recent trials have shown can arise 
when attempting to extract the maximum instrumental accuracy from a receiver 
carried in a survey aircraft. Among the refinements to be incorporated in future 
Decca air-survey receivers are an improved method of applying and recording the 
‘reference’ correction, and the use of electronically-controlled ovens for the crystal 
filters—a technique already employed at the transmitting stations. In regard to the 
Flight Log, a considerable reduction in weight has already been made (the complete 
helicopter-type Flight Log weighs 35 1b.) and it is intended to apply to air survey 
tracking the skewed-primaries technique referred to above. 
6.2. The ground stations are capable of ‘miniaturization’ to a considerable 
extent. One of the impending developments in this connection is based on a variant 
of the system that is already being produced for the Hydrographic Department of 
the British Admiralty to safeguard the operation of Two-Range chains in tropical 
areas where the ambient noise level is high. In this, a different harmonic relation- 
ship is employed between master and slave frequencies such that the master uses 
the highest of the three frequencies and is thus able to radiate several times more 
power than formerly from a given aerial system. Conversely, this arrangement is 
expected to make possible a considerable reduction in the size of the transmitting 
aerials required for mobile ground stations used in air surveys. 
6.3. Developments under the ‘propagational’ heading will be aimed primarily 
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