RCA ET-4310

GENERAL DESCRIPTION

IMPROVED SERVICE FOR CBS FOREIGN LISTENERS

photo RCA ET-4310

New Facilities Provide Entertainment for Many Lands

A London bus-driver, a tea salesman in Sidney, a bridge engineer in Brazil, and a retired army captain in New Zealand - these are some of the thousands of short-wave listeners all over the world who have written in to the Columbia Broadcasting System requesting verification cards on W2XE, Columbia's new international shortwave transmitter at Wayne, N. J.

The station has been in operation since 1929. Early this year, however, the installation of a completely new transmitter has caused letters to pour in to the station from every corner of the globe. The high-fidelity transmitter is licensed to operate on the frequencies 6120, 11830, 15270, 17760, and 21520 kc /sec. The equipment used is the RCA ET4310, 10 KW short wave transmitter.

Short-wave tests for determining the effectiveness of directional antennas were recently undertaken by station W2XE in collaboration with the British Broadcasting Corporation. The tests are being conducted under the auspices of the Union Internationale de Radiodiffusion (International Broadcasting Union) at Brussels, Belgium. Data uncovered by the tests are to be used as the basis for recommendations to the forthcoming world radio conference in Cairo, Egypt. During the course of the test transmissions, W2XE will operate during the next few months on the following schedule:

Freq'cy	Time	Antenna Direction
21,520 kc	1130-1400 G.M.T. 1400-1430 G.M.T.	Europe South America
15,270 kc	1900-2130 G.M.T. 2130-2200 G.M.T.	Europe South America
11,830 kc	2230-2300 G.M.T. 2300-0400 G.M.T.	Europe South America

W2XE Program Facilities

The growing importance of short wave program transmission on a world-wide basis has led to Columbia's establishment of a special W2XE program department, located in CBS headquarters at 485 Madison Avenue in New York. In charge of the department is Miss Elizabeth -Ann Tucker, formerly of the CBS General Engineering staff. Programs of exceptional international interest over the nation-wide network of the Columbia Broadcasting System are broadcast over W2XE with announcements in four languages - French, English, German and Spanish. Other programs are arranged expressly for W2XE's international audiences and are not heard over the national network.

The increasing number of short-wave and all-wave receivers in all countries has opened up a vast new audience for W2XE's program offerings. "D.X.-ing" is no longer the exclusive pleasure of technically-minded listeners, but has spread to thousands wholly unschooled in radio engineering. Their demand is for the best in entertainment, and Columbia is making an effort to provide it for them at peak listening hours in both hemispheres.

Technical Facilities

The W2XE technical facilities provide equipment for short-wave international broadcast service and incorporate the latest developments of the radio art, developments which heretofore have been applied only to transmitters operating at conventional intermediate or low broadcast frequencies. These developments include such features as all a-c operation, high level modulation, elimination of fuses in all power and control circuits, substitution of ceramic coils in place of the rubber hose coils previously used for insulating the high power vacuum tubes from the water supply and the elimination of all wood insulation from the equipment. The new plant has exceptional fidelity characteristics. The audio frequency characteristic of the transmitter is substantially flat between the frequencies from 30 to 10,000 cps. The response is uniform within 1 db from 100 to 5000 cps and within ± 1.5 db from 30 to 10,000 cps. The r-m-s values of audio harmonic distortion, within the range of 50 to 7500 cps, do not exceed 4% for any single modulating frequency between 0 and 100% modulation.

The unweighted overall noise level at this transmitter is more than 50 db below 100% modulation. This low level is partially secured through a-c filament operation. Low level audio frequency amplifier tubes are provided with indirectly heated uni-potential cathodes. All radio and audio stages are connected in push-pull, and an additional reduction in hum is obtained by connecting the tube filaments in the last radio stage on a two-phase supply, thus partially cancelling the hum. Hum compensating apparatus is employed which introduces into the audio stages 60, 120 and 180 cps, 180 degrees out of phase, with similar frequencies generated by the transmitting equipment.

The carrier frequency range of this station is from 6.0 mc to 21.52 mc. Each operating frequency is maintained constant by quartz crystal control. The quartz plates used are cut on a special axis with respect to the X and Y axis of the crystal and as a result the frequency variation with change in crystal temperature is negligible. Furthermore, these crystals have a high output and stable, parasitic-free operation. The frequency deviation of this station does not exceed plus or minus 0.01 of 1%.

Quartz Crystals

Four quartz crystals are provided, each with its own oven. The complete oven is equipped with plugs and may be quickly and easily removed to be replaced by another unit. Any two crystals may be switched into the operating circuit and then become part of the frequency change mechanism. The proper crystal is selected by the frequency change switch. The crystal oscillator circuit is one which has resulted from considerable research and development. It combines high output with stable, constant frequency operation. Provision is made for slight frequency changes by manual control, without resorting to changing the dimensions or adjustments of the crystal itself.

The crystal oscillator is followed by a buffer stage, a frequency doubler stage, a second doubler, and two amplifier stages, which operate at the fundamental frequency. The final amplifier utilizes two water cooled tubes. Each stage is shielded and the output stage is connected in push-pull and neutralized. Adequate insulation is provided to prevent break-downs which might be caused by over-modulation surges.

The problem of high speed frequency change was solved by providing two independent tank circuits for each stage, one for each of the two frequencies it is desired to use. All adjustments for each frequency may thus be permanently set up independently, with the assurance that no change made for one frequency will affect tuning on the other frequency. The power amplifier tank circuit adjustment is accomplished by a solenoid operated frequency change switch which permits instantaneous frequency change by means of a single switch.

Audio System

The audio system consists of two push-pull amplifier stages, and a high level Class B modulator. The modulator, which also employs two large water cooled tubes, is coupled to the radio frequency output stage through a transformer. A filter prevents the d-c components of plate current from flowing through the transformer.

Three rectifiers provide all of the d-c voltages required in the transmitter. The first consists of two hot cathode, mercury vapor tubes, in a single phase full wave circuit. The rectifier develops approximately 2500 volts d.c. It supplies plate voltage for the crystal oscillator and the buffer amplifier. It also supplies bias voltage for the second audio amplifier and modulator. The second rectifier employs three mercury vapor rectifiers in a three phase, half wave, rectifier and supplies 1800 volts d.c. for the intermediate power amplifier and the two frequency doubling stages. This potential is reduced to 1300 volts for the first frequency doubler, and 1600 volts for the second doubler. The main rectifier consists of twelve hot cathode, mercury vapor rectifier tubes in a double three phase, full wave circuit. The two-three phase sections are connected in series. The d-c output voltage is 10,500 volts. Taps are provided at 50 and 75% maximum voltage

An automatic induction voltage regulator is supplied which regulates the line voltage to a constant value for the entire transmitter eliminating all difficulty with fluctuating voltages and output. The regulator will compensate for a 10% change in primary power supply.

Protective Devices

Protective devices guard against excess plate current and inadequate flow or excessive temperature of cooling water. Reliability is insured by simplicity of design and conservative rating, while meters in radio and power circuits make it possible to observe operating conditions at all times.

A closed circuit cooling system is supplied, consisting of a circulating pump, radiator and blower assembly and a supply tank. Distilled water is used since water of high mineral content causes scale formation on the anodes of the radiotrons. Since the entire water system consists of porcelain and copper, there is no chance of contamination of the water, which may therefore be used for long periods without replacement. The water cooling system, which requires approximately 60 gallons of water, has a cooling capacity conservatively rated at 25 kw continuously for an ambient temperature not exceeding 115 degrees F.

Directional Antenna Systems

W2XE is primarily interested in serving Europe and Central and South America. To increase the field strength of this station in these directions, antennas have been erected, and are now in daily use, capable of giving an average gain of ten times in desired areas. European coverage, from directional antenna design standpoint, is not as difficult as South American coverage since the great circle paths from New York to most of the important cities in Europe lie within a relatively narrow angle; wheras coverage over the greater part of South America requires antennas which have an appreciable gain over an angle of from 35 to 40 degrees. Non-directive and semi-directive antennas are also available for use when directivity is not required. Each of the antennas is fed by transmission lines which are matched and balanced. These lines are connected to a unique rotary switch which permits a rapid selection of any one of six antennas now available.

TUBE COMPLEMENT
RF stages		AF stages and modulator		Rectifiers
Number	Type	Number	Type	Number	Type

THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES
	ITU	Country	ITU	Country
	USA	USA