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The APK-15M Radio Compass is found in many Russian or East block aircraft, ranging from the Antonov 2 biplane to the Mig 29 and Sukhoi SU27 air superiority fighters. In the Yak 52 sporting aircraft, Radio compass control panels are fitted in both cockpits. The rotary channel selector knob allows the selection of a total of 8 channels in two banks of four. The selector knob is marked 1, 2, 3, 4 & ï. ï meaning "Variable". (A feature not fitted to the Yak 52.) The oddly placed switch, on the left underside of the glare shield, which is marked A and b allows the selection of two banks of channels so a total of eight channels are selectable. Originally its use was outer and inner beacons for 4 airports. In line behind the brown Bakelite flight recorder (left side of the fuselage, if fitted) are to be found two small rectangular boxes mounted next to each other. They are about five inches tall and two inches wide. Each is black with silver writing on it. The left box (looking in the a/c) is refereed to as the A box, the right as the b box. Inside each box, you will find four rows of four rotary switches marked, from the top, I, II, III & IV. The following table is intended to show which row of switches, in which box, set the frequencies for each channel on the selector in the cockpit. It is easier to think outer and inner marker. So switch set "in cockpit" is inner marker (channel) and switch "out" of cockpit is outer marker (channel). The switch toggles left - right. A is "outer" marker switch to the left position. ADF Channel / Box / Row A 1 — Left — Row I b 1 — Left — Row II A 2 — Left — Row III b 2 — Left — Row IV A 3 — Right — Row I b 3 — Right — Row II A 4 — Right — Row III b 4 — Right — Row IV Table A Now the easy part. Having determined which row of switches to change, simply set the first three switches (from the left) to the frequency you require. As you will see from the markings, set hundreds of KHz on the leftmost switch, tens on the second switch and units on the third switch. If the frequency you require is greater than 999.5 KHz (ie, 4 digits) ignore the first digit. (set 234 for 1234 KHz) The fourth switch (the rightmost) has two functions. It is used to set 0.5 or 0 KHz and to select the frequency band in which your chosen frequency lies. The switch has TEN positions marked: I 0, I .5, II 0, II .5 etc. Set the switch to the Roman numeral as indicated below and to the 0 or .5 KHz position as required. Note the frequency band! For 234khz use selector position II and 1234khz use selector position V. Frequency range / Band Position 150 → 239.5 KHz — Band I 240 → 399.5 KHz — Band II 400 → 699.5 KHz — Band III 700 → 1199.5 KHz — Band IV 1199.5 → 1799.5 KHz — Band V Table B That completes the procedure. Good luck!