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COT Division, 1st Session - Final Report  35
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comparison of phases between two radiated radio frequency field patterns. One of these patterns is essentially nondirectional and is modulated at a frequency of 10 kc/s. (constantamplitude)which is, in turn, frequency modulated at 30 cps with a deviation ratio of 16. This is the reference pattern. The other pattern contains two very sharp nulls in the direction of the course, and represents sideband energy of 30 cps, amplitude modulation. due to the reversal of modulation phase at the null pints, one side of the pattern will have modulation in phase with the reference pattern, the other side will have modulation out of phase with the reference pattern. Along the nulls, there is no signal for comparison with the reference, and the aircraft instrument indicates "on-course". To either side of the nulls, there is a rapid increase of signal and the instrument will indicate "off-course" to right or left.

2.2.2. The modulation of the carrier shall be:
a) Thirty per cent by the 10 kc/s. subcarrier;
b) Thirty per cent by the sideband pattern (maximum);
c) Thirty-five per cent by speech maximum.

2.2.3. A simultaneous communication channel on the same carrier frequency used for the localizer function shall be provided.

2.2.4. Paragraphs 2.1.1, 2.1.7, 2.1.8, 2.1.9 and 2.1.10 shall apply also to the phase-comparison type of localizer. 

3.--UHF Glide Path Transmitter

3.1. The UHF glide path transmitter (hereinafter referred to as GPT) shall operate in the band 328.6 Mc/s. to 335.4 Mc/s. and shall utilize horizontal polarization.

3.2. The GPT shall produce a course by the intersection of two radiated radio frequency field patterns. One of these patterns shall be modulated at a frequency of 150 cps, and the other at a frequency of 90 cps. The amplitude of the modulations shall be equal along the intersection of the patterns.

3.3. A glide path course shall be provided in the vertical plan containing the runway centre line and shall be adjustable in glide angle from 2 degrees to 4 degrees with respect to the horizontal, measured from the point of contact.

3.4. The audio modulation frequencies shall be so arranged that the 90 cps signal appears above the glide path course and 150 cps signal appears below the course.

3.5. The glide path needle of the crossed pointer instrument shall show full scale "fly-down" indication for a deviation of 0.3[degree symbol] above the glide path, and full scale "fly-up" indication for a deviation of 0.5[degree symbol] below the glide path when measured along the centre line of the runway with a standard receiver.

3.6. An automatically operated glide path monitor should be provided at a distance in front of the glide path antenna system. The monitor shall transmit a warning to the remote control point if the glide path equipment becomes inoperative or if the angle of the glide path should deviate more than 5 per cent from normal.

3.7. The GPT shall be located at such distance from the approach end of the runway that, at a point 3, 500 feet (1,070 m) from the approach end of the runway, the glide path course will be 200 feet (60 m) above the elevation of the runway. This shall hold for the course set at a glide angle of not less than 2 degrees nor more than 2 3/4 degrees, measured at the point of contact. The GPT should be not less than 400 feet (120 m) and preferably not more than 550 feet (170 m) from the centre line of the runway being served; nor closer than 750 feet (230 m) to the approach end of that runway.

4.--VHF Marker Beacon
4.1. VHF marker beacons shall operate at 75 Mc/s.

4.2. the marker beacons shall be located as follows:

a) Boundary marker: 250 ft. +/- 25 ft. (75 m +/- 7.5 m) from the approach end of the runway and 200 ft. (60 m) to the left of the centre line thereof;

b) Middle marker: 3,500 ft. +/- 500 ft. (1,070 m +/- 150 m) from the approach end of the runway and not more than 250 ft. (75 m) from the extended centre line thereof;

c) Outer marker 4-1/2 miles +/- 1,000 ft. (7,240 m +/- 305 m) from the approach end of the runway and not more than 250 ft. (75 m) from the extended centre line thereof.

4.3. The marker beacon transmitter shall deliver approximately 3 watts of carrier energy modulated 100 per cent to an antenna system consisting of two half-wave antennas in line, excited in phase and spaced one-quarter wave length above a counterpoise. The axis of the antenna shall be parallel to the approach line.

4.4. the modulation frequencies shall be as follows:
 
a) Boundary marker: 3,000 cps;