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FAQ (Frequently Asked Questions)


Rotor radar system

Radar Type 15 GCI


The following information is reproduced from SD 727, Part 2 , Section 3, Chapter 2: (A.L. 2, Oct 58)

Range Performance

17. Three alternative transmitting radiation patterns can be had by selection from the Console 61, as described in para. 12: these patterns are shown in Fig. 7 for a mean aerial height of 11 feet 3 inches and a frequency of 200 Mc/s. With no diode-switching (i.e. when the Console 61 height key is in the NORMAL position),the V.P.Ds. correspond to these patterns, as shown in Fig. 8 (which illustrates reliable pick-up ranges on a Meteor NFl 1 at 209 Mc/s with a mean aerial height of 12 feet 3 inches). The normal position is PHASE, and ANTIPHASE serves for gap-filling. Diode-switching (height key in position HEIGHT or PHASE) gives an effectively solid receiving radiation pattern, but does not alter the transmitting pattern and thus does not greatly help in gap-filling; it effectively halves the receiving aerial gain,, and so decreases detection ranges by about 20 per cent. The TOP position of the phasing key is not, normally required; it was expected to give improved low cover for use in surface-watching, but apparently it fails to do this.


18. The ideal site for a Type l5 is a flat and uniform surface. Any significant departure from flatness or change in the nature of the surface causes variation of the V.P.D. with azimuth, and height-finding then becomes un-reliable. The limits of deviation from flatness may be taken as increasing from + 6 feet at 100 yards to ▒ 30 to 40 feet at half a mile from the radar. The site should be flat in this sense for half a mile from the radar in all directions, save for small isolated irregularities (such as single houses, trees, or ditches). If a flat site cannot be found, it is permissible to put the radar at a spot from which the ground slopes uniformly away in all directions, up or down. The slope should not be greater than 1/2o, i.e. ▒ 6 feet at 100 yards, ▒ 50 feet at half a mile. High ground may act as a reflector or as a screen: a hill closer than three to four miles generally upsets the interference pattern and destroys the height calibration on its azimuth; while high ground beyond about four miles (provided it is not a sharp ridge) does not have this effect but may act as an efficient screen for reflections from more distant hills, thus helping to reduce P.E. clutter. An ideal screen for this purpose is ground rising rapidly to 300 to 400 feet at about four miles from the radar, with a gradual rise for several miles beyond it.

19. It is obvious that a site flat enough for a Type 15 cannot reliably be chosen simply from inspection. The correct way to select a site is to examine a survey map of the area (with a scale of not less than one inch to a mile, and contours at 50-feet intervals), looking first for regions without local high ground and with widely spaced contours (variations of not more than 50 feet in a mile); this study will probably bring to light several possible locations, each of which should then be checked against the principles of para. 18 by taking four or more cross-sections on different bearings showing height against distance. The most likely site will now be indicated, but a final choice can be made only by actual inspection of the ground within a mile of the chosen site, since Within that area irregularities too small to be recorded on the map could make the site unsuitable. It is well to be prepared with several alternatives, because the best radar site may be unacceptable from the point of view of accessibility, defence,camouflage, or communications.

The information above is reproduced from SD 727, Part 2 , Section 3, Chapter 2: (A.L. 2, Oct 58)

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 Updated 22/09/2003

Constructed by Dick Barrett


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ęCopyright 2000-2003 Dick Barrett

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