Radio broadcast .. (1922-30)

UX-171A 22ov -- GEN + REDO 40 MILS O STORAGE BATTERY GEN- - « POWER SUPPLY SET --' • REMOTE CONTROL • Rl-13 OHMS R2-3000 OHMS R3- 0.5 MEGOHM R4 - BALLAST RES R5-150 OHMS C1-OQ005MFD C2- TRIMMER C3 - 0.1 MFD. C4- 2 MFD. C5- 1MFD. Cll- 0.01 MFD. C6- 0.06 MFD C7 - 0.0025 MFD C8- 2 MFD. C9 - tt03 MFD. CIO- 250 MMFD. The schematic diagram of a typical air-beacon receiver Three types of radio receivers are in general use by aircraft. These are: (1) Military type that is required to cover a broad band of frequencies. (2) The average commercial beacon and radiophone receiver required to cover the comparatively narrow band from 285 to 350 kc. (3) The high-frequency receiver that operates on frequencies above 1500 kc. The first type has rather rigid specifications and usually requires the use of a specialist in operat- ing. The second type is a standard tuned-radio-frequency receiver, and usually consists of three tuned stages of screen-grid radio- frequency amplification, a detec- tor, and two stages of audio- frequency amplification with sufficient output to operate a beacon-indicating device. The third type usually consists of a regenerative receiver employ- ing plug-in coils for the different frequency bands and sufficient a.f. amplification for easy reception above the mechanical noises. The general requirements of a radio receiver for aircraft use are as follows: 1. Single dial control. Fixed tuning. 2. Rugged volume control. Capable of remote installation. 3. Sufficient shielding to limit signal pick-up to that of the an- tenna. 4. Rugged construction in or- der to be immune from vibration en- countered. 5. Npn-microphonic construction. 6. Rigid condenser plates. Wide spacing with plates of at least 0.025-inch stock is usual practise. 7. Non-microphonic tubes. Tubes of the heater type such as UY-227 and uv-224 are particularly adapted for aircraft use. (The great demand, particularly by the aircraft industry, for a non-microphonic low-current-consumption tube has resulted in the development of the ux-864 type. This tube has approximately the same characteristics as the ux-199, except that it uses an oxide-coated filament requiring 0.250 amperes at 1.1 volts. This tube is extremely rugged, non-microphonic, and View of a wind-driven motor generator. economical in operation.) It is understood that a complete line of low-current, low- voltage, non-microphonic tubes are being developed. 8. Accessibility or ease of servicing. The receiver mounted on a track with a locking control is quite satisfactory. 9. Dash control. This consists of vol- ume control, on-off switch, tuning device,. beacon indicator, jack for phones, and necessary cable connections. 10. Of such size and dimensions which permit installation in whatever space is available. 11. Sufficient sensitivity to get down to atmospheric noise level with a 2-meter vertical-rod antenna. 12. Sufficient fidelity. Reacon signals are modulated from 40 to 120 cycles and the voice ranges from 300 to 3000 cycles. 13. Must have sufficient out- put to operate a beacon course- indicating instrument. Ten volts of audio frequency with a load impedance of 4000 to 7000 ohms is sufficient. 14. A fair amount of selectivity is necessary, although the prob- lem is not yet as bad as that on the broadcast frequencies. 15. A well-designed helmet to exclude mechanical noises. Use of sponge rubber caps is satisfactory. 16. Should be satisfactory for both visual and aural beacon re- ception up to 150 miles with a 2-kw transmitter on the ground on the 333-kc. band, using an antenna 2 meters high on the plane, and the bonded metal members of the plane for a counterpoise. 17. The total weight, including a 5-pound duralumin antenna • and a 10-pound battery, should not exceed approximately 35 pounds. The battery used for the navigating and landing lights may be used for the filament supply of the receiver. Plate rectification with automatic grid bias is desirable when used with a visual indicator. Reversal or lack of course in- dications may result if the input is in- creased through values corresponding to the maxima of the curve into the regions of the negative slope. An automatic bias prevents this. The sensitivity and selec- RADIO BROADCAST FOR APRIL • 331