Navigational Aids
Consol
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Major system characteristics |
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System type |
Rotating beam beacon navigation system |
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Frequency band |
Medium Frequency (MF) |
The text that follows in this section is taken from "The Services Textbook of Radio, Volume 7, Radiolocation Techniques" by Brig. J. D. Haigh, O.B.E., M.A., M.I.E.E., Edited by the staff of "Wireless World", H.M.S.O., London, 1960 pages 254 - 256. This volume was known to the British armed forces as Admiralty B.R.600(7), War Office 10224(7) and Air Ministry A.P.3214(7).
Consol
The last system to be described is really a development of the rotating beacon systems described in Chapter 3. It is a medium frequency system and therefore liable to ionospheric disturbance at night, but it is claimed that the resulting inaccuracies are not nearly as serious as in medium frequency direction finding. An an example, the practical daytime accuracies are quoted as ± 1 /2o on the normal to the base line and ± 1o at 70o to the normal, whereas at night the figures quoted are ± lo on the normal to the base line and ± 2o at 70o to the normal. The latter figures are for a range of 300 nautical miles. Beyond this range the accuracy is said to improve.
Consol was developed in Germany and was known by them as 'Sonne'. It was the main navigational aid used by them during the war.
A Consol station consists of three aerials sited in a straight line with an aerial spacing of a small number of wavelengths. The two outer aerials are fed with one quarter the current of the centre aerial and the power in one leads, and in the other lags in phase that in the centre aerial by 90o. In these conditions a complicated polar diagram is produced which is shown in Fig. 17.12 (This is the diagram for 3l aerial spacing).
By interchanging the phases of the two outer aerials the polar diagram becomes the mirror image of that previously shown. The two polar diagrams are shown in Fig. l7.l3.
A switching arrangement maintains the full line diagram for the time of a dot (1/8 sec) and the dotted diagram for the time of a dash (3 /8 sec). In this way a number of equi-signal directions are established which have to be distinguished one from another by direction finding or by any other navigational process. The important feature of Consol is the means provided for determining positions intermediate between the equi-signal directions. This is achieved by slowly changing the phases of the two outer aerials in such a way that after the period of the 'sweep, as it is called, the two aerials have interchanged their phases. This slow phase change is additional and quite separate from the regular dot-dash alternation of phase. The effect of the sweep is to rotate the dot and dash sectors in the direction of the arrows shown in Fig. 17.13. The complete cycle of transmissions, in the British system, is as follows:
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Omni-directioual signal from centre aerial keyed with station call sign |
6 seconds |
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Break |
2 seconds |
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Dot-dash alternation and phase sweep |
30 seconds |
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Break |
2 seconds |
An observer at P in Fig. 17.13 will know, by other navigational means the bearings, with respect to the beacon, of the two equi signal directions between which he is situated. After hearing the beacons call sign he will hear a number of dashes which, as the polar diagram rotates will, after a time, merge into a continuous tone after which dots will be heard. By counting the number of dashes before the equi signal the precise bearing of the observer with respect to the beacon can be computed. In practice, charts are issued with an overprint of great circles diverging from the beacon numbered with the number of characters (either dots or dashes) which will be heard before the equi signal.
The accuracy of Consol could be increased by making the angular separation of the equi-signal directions smaller (this can be done by increasing the aerial spacing) but the limit is set by the necessity of being able, by direction finding or by any other navigational process, to determine between which two equi-signal directions the present position falls. This has led to the decision that 100 shall be the minimum separation of equi-signal directions.
