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Aviation History
1962
1962 - 0443.PDF
FLIGHT International, 22 March 1962 can be expanded by carrying spare pairs of crystals and doing some fiddling in the air. Even lower on the scale are the radios with crystal-controlled transmitter channels on a dozen or a score of frequencies and a continuous tunable teceiver. The problem is obviously to tune the receiver exactly to the correct frequency. In some cases this can be done only while the ground station transmits in reply to a call, which it rarely does for more than a couple of seconds at a time. The pilot will probably have to ask for a lOsec transmission from the ground for tuning his receiver—and this wastes everyone's time. Most of the tunable-receiver sets have "whistle stop" tuning. When the function selector switch is set to "calibrate" or "tune," part of the transmitter output is fed into the receiver and the pilot can tune for the loudest point or "vanishing point" in a tone signal. Even so, hand tuning can be rather a chore. In more elaborate radios, the frequency coverage is extended from 190 channels to cover the top end of the civil communications band, or it is designed to cover the complete band from 108.0Mc/s to 135.95Mc/s in 50kc/s steps, making 560 receiver channels in all. A few radios provide coverage beyond the 136.0Mc/s, and some of the "random" 20- and 40-channel sets can accept higher crystals. Relatively few of the 50kc/s frequencies have yet been allocated for specific services; certainly none would yet be required by the average private pilot. Although radios catering for 200kc/s spacing are still being made and are still legal, the even tenths of Megacycles have been very widely allocated and lOOkc/s spacing is desirable. When the tighter spacing actually becomes mandatory, the 200kc/s sets may have to be slightly modified to prevent their causing inter ference with neighbouring frequencies. There are a number of reliable and cheap, but unnecessarily cumbersome, radios providing between four and 20 channels. The customer must make up his own mind, but should seriously consider that for what may after all be a feasible increase in cost he could increase his capacity ten-fold by fitting a full 90-channel set and that this would weigh much less than the older set, use a fraction of the power and prove very much more useful. A pair of crystals costs about three guineas. The 360-channel sets would therefore be much more expensive if they did not build up, by multiplication circuitry, the 360 frequencies from a set of about 30 or 40 crystals. One particularly small radio gets 90 channels from one crystal! How many frequencies does the private pilot need ? The answer probably is "more and more." Radio makes it possible to fly to certain airfields where radio is mandatory, to obtain weather information and DF bearings which may prove extremely helpful in marginal weather. The more one learns about the various services, the more one depends on the assistance they can give. It is probably true to say that, particularly in Britain, the more you want from your radio, the more frequencies you must have. On the Continent, and indeed right out to Hong Kong and points east, you can get bearings and airfield control on 118.1 and 119.7Mc/s. It is always advisable to cover the eventual emergency, to carry 121.5Mc/s; and 117.9Mc/s, the military common frequency, is always handy A Motorola "two and a half" system, with ADF, on the racks at Smiths Aviation Division factory at Cheltenham. Note three receivers, two transmitters, ADF tuner and bearing dial and two VOR/JLS cross (jointers. The "black boxes" are three power packs, glide-slope receiver and two VO R/Loc converters 443 London Airways (126.7) and Preston (125.5) offer half-hourly weather broadcasts, and there may be a favourite funk-hole—some where open after dark and equipped with GCA or VHF/DF— needing several frequencies. It all mounts up pretty soon to the point where a dozen channels are hardly sufficient and allow little room for the odd frequency needed for an occasional visit. There is no doubt that the sensible step is get the lot if you can possibly afford it. It is also well worthwhile studying radio facilities to find out what assistance and information you can get. Borrow Inter national Aeradio Flight Guide or a Jeppesen manual, or get helped through the legal jargon of the Air Pilot. All these are expensive, so buy them only if you are sure you need them. To avoid legal trouble, obtain from HMSO a copy of pamphlet CAP.46, learn radio procedures, take the very simple practical exam and obtain the necessary radio licence (exam and licence fees £2 10s). Then work hard to make your RT patter smooth, crisp and economical. Learn to put your meaning across unequivocally without wasting a single word. Skilled operation pays off in ready acceptance by ground station operators, and more willing assistance. Your RT is your visiting card. Navigating: by Radio IT would be difficult to chose between communications and navi gation radio in a light aircraft. Ultimately navigation is probably the most useful, but ideally you should have both; and the arrange ment of the 190-channel VHF radios makes this relatively simple. The receiver already covers the VHF navigation band and all that is needed to make use of VOR beacons and ILS localizers is the converter and indicator, generally supplied as a single unit and costing perhaps two-thirds as much as the original communica tions radio. VOR is now well distributed in Britain and over the Continent and is extremely easy to use in the air. The range over which it will operate depends on the height of the receiving aircraft (because VHF travels in line of sight only) and the quality of the receiver. Airline-quality VOR might have twice the range and performance of one of the little basic receivers, but the latter can still give good reception at 60 miles at 4,000ft and it makes an invaluable navaid. The Narco Omnigator would probably provide cross-bearings from one or other pair of VORs over most of southern England at 2,000ft. The VOR indicator in the cockpit is a bearing dial and a left-right needle. Remember that the VOR beacon is continuously projecting a complete ring of actual magnetic bearing lines at one-degree inter vals. With the airborne receiver you are finding out on which of those lines the aircraft lies. Select the frequency of the beacon, check its morse identification transmitted every 15 or 30sec, and then turn the bearing dial on the VOR indicator until the needle centres. That is the bearing line from the beacon which passes through the aircraft. A bearing line can, of course, be called 270° inbound, QDM or "To," or 090° outbound, QDR or "From." If, after you tune a beacon, you twiddle the bearing selector until the needle centres, and it says 270°, a little flag will also appear in the dial say ing "From" or "To." On most indicators you will be able to see the reciprocal bearing at the bottom of the bearing dial and you can twiddle it to the top if you want 270° To instead of 090° From. The flag will then change from "To" to "From." Explanations become tedious beyond this point, and lOmin in the air are worth hours on the ground. The technique is either to centre the needle and read off the bearing, or to select a bearing, fly a suitable magnetic compass heading until the needle centres and then fly to keep the needle centred. Landmarks or airfields all lie on VOR radial bearings. Assess the appropriate radial on a map, fly along it and you will pass over your landmark. If the VOR signal is not strong enough to use, or the set has failed, a little flag marked "Off" will appear. Everyone knows that ILS is the instrument landing system used for final approach at airfields. If you have a VOR receiver you will also be able to follow the ILS localizer, or course beam, using the left-right needle of your VOR indicator, with the runway bearing set in the course dial. The characteristics of the receiver are auto matically changed to accept ILS guidance. ILS localizer beams can be used to home to a runway in poor visibility, or as bearing lines for cross-country flying, although localizer accuracy is not usually guaranteed at more than about 15 miles from the runway. To make a full ILS approach for a landing in low ceiling, a glide-
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