The Short Waves: W3XAU – Philadelphia 

26 March 2024


Cover of World-Radio

From World-Radio, dated 15 March 1935

The short-wave station W3XAU, used in conjunction with the 50-kilowatt transmitter WCAU, has been in daily operation since 1929. It was originally licensed for 500 watts, and the transmitter was situated at Byberry, Pennsylvania. In 1932 the power was increased to 1,000 watts and the transmitter was moved to the new station building, of which a photograph is shown, at Newtown Square, Pennsylvania. This is 12.8 miles air distance from the studio building, which is in the heart of metropolitan Philadelphia.

Both the short-wave and medium-wave transmitters are installed on the upper floor of the building shown, and the rotating machinery — water pumps, cooling system, etc. — on the ground floor. The transmitter itself consists of three units—the oscillator, power amplifier, and rectifier. A single crystal oscillator unit is used for both operating frequencies — 9,590 and 6,060 kc/s. The crystals, of course, are contained in a thermostatically controlled heat chamber with adequate insulation from the outside air.

The oscillator output is fed to a frequency doubler, thence to two screened-grid intermediate amplifiers and to the modulated R.F. amplifier and finally the water-cooled power amplifier, which has an output rating of 5 kilowatts. The final power amplifier is operated as a linear amplifier and delivers a carrier output of 1 kilowatt at 100 per cent. modulation.

All the valves and their associated circuits — with the exception of the water-cooled amplifier — are contained in the exciter unit. The final power amplifier, the water-cooling system, and the output circuits are contained in the second unit.


A man tends electronic equipment

The 1kW short-wave transmitter described in the article


The third panel — shown oh the right of the accompanying illustration — contains a three-phase full-wave mercury-vapour rectifier, which delivers 5,000 volts to the anode of the water-cooled power valve, as well as furnishing the necessary anode voltages for all the smaller valves.

The output of the transmitter is fed into two 500-ohm transmission lines which lead to two half-wave vertical aerial systems, erected one on each side of an 85-foot wooden mast. A separate transmission line and aerial is used for each frequency, with suitable switches mounted overhead for rapid change from one to the other. Switches are also provided for changing the constants of the transmitter circuits to allow operation on either of the assigned frequencies.


Transmitter building

Station WCAU and W3XAU. The transmitter house at Newtown Square, Pennsylvania


A tall building

WCAU studio building in Philadelphia

The programme carried by W3XAU is usually that of the mediumwave station, WCAU. These programmes emanate from the studio building at 1,622, Chestnut Street — where eight studios (including an auditorium), their associated control rooms, a master control room, and other quarters incidental to a broadcast station, are situated — and are carried to the transmitter over high-quality telephone circuits.

The radio equipment contained in the studio building is RCA Victor manufacture and was put into operation on December 25, 1932. It is operated entirely from 110-volt A C. mains, and is capable of faithful reproduction from 30 to practically 10,000 cycles. The RCA Victor velocity microphones are used throughout, giving an excellent over-all frequency characteristic from microphone to transmitter output. WCAU, and its short-wave transmitter, W3XAU, are members of the Columbia Broadcasting System, and approximately 50 per cent of the programmes radiated by both stations are received from that network.

Letters reporting reception of W3XAU have been received from practically every State in the United States and from almost every foreign country in the world. The majority of the letters are received from the British Isles, which may be due to either unintentional directional transmission, or to the popularity of short-wave receivers there.

All reports of transmissions from W3XAU are acknowledged, and verified if the information contained corresponds with the records. Comments are always welcomed, especially those received from foreign countries.


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