TELEVISION at WBZ

TV Facilities at New Center Include Four Major Points
of Operation: TV Equipment Room with Sight and Sound
Setup (Audio Facilities Include Consolette Which Permits
Four Studio Microphone Positions, Two Turntable and
Six Remote Input Positions for Projectors, Network Line,
Remote Lines and Speaker Monitors) ; Projection
Equipment (16-mm and Two 35-mm Film Units) ; TV/FM
Transmitters, and Mobile Televan. Three-Bay TV
Batwing and Two-Bay FM Pylon Mounted on Tower 656’
Above Sea Level.

TELEVISION IN BOSTON . . January, February, March, April, May and finally T-Day, June 9, 1948.

At first, it was hoped that WBZ-TV would be on the air by early spring. Winter came upon us early last December and from then until late spring the erection of our tower was at a standstill.

Many days were too cold and windy, making it impossible for the riggers to work. For a full two months it was a continual battle in an attempt to keep the snow cleared from the tower steel. New England’s worst winter in decades continued to be equally discouraging throughout the months of April and May. When it came time to hoist the TV pylon and super turnstile antennas atop the tower, it took a period of two weeks to do a routine three-day operation.

While this activity was going on outside, we lost little time within the confines of our building. Plumbers, bricklayers, carpenters, plasterers, etc., were busily laboring at their specific duties and in the middle of all this activity, our own crew was diligently working on the installation of our 5-kw television transmitter under the supervision of William C. Ellsworth, Westinghouse headquarter's engineer from Philadelphia.

Last January we were fortunate to be able to obtain two sets of RCA TK-30A field camera equipment. This gear was set up in an antiquated studio of WBZ, then located at the Hotel Bradford in downtown Boston. This enabled us to form our technical staff to obtain firsthand working knowledge of the equipment prior to the time we would have to use it on the air.

Television interest in Boston actually got underway last December when NBC fed the Louis-Walcott fight for studio viewing. The program was piped in over the A. T. & T. microwave relay link into Bowdoin Square, from which point the New England
Telephone and Telegraph Company land wire facilities carried it to the WBZ studios. Over two hundred people viewed this telecast, received on nine "jeeped" receivers.

This instigated a series of feeds from NBC to WBZ which were sponsored by various receiver manufacturers. The demonstrations also afforded manufacturers an opportunity to set up receiver distributors throughout this area in anticipation of a signal emanating from WBZ-TV.

In April, television gained still more headway. In cooperation with the Boston Post, WBZ-TV and the Electric Institute of Boston, it was decided that television should be a keynote of Boston’s First Annual Electric Show. Arrangements were made with various receiver manufacturers and distributors to set up over 100 receivers to be located at various booths at the show.

This presented two serious problems: the distribution of both video and audio and (2), program makeup. The first problem was negotiated successfully by building a group of wide-band video distribution amplifiers and by stringing miles of coaxial cable all over Mechanics Building. Receiver manufacturers were then required to supply "jeeped" receivers. Jeep applies to the conversion of a standard TV receiver chassis so that it will take a standard 2-volt video signal, rather than picking up the television signal direct front the antenna, In reality, it is much like a phono audio input on a receiver where, the audio is injected after the second detector, rather than deriving the signal through the rf and if stages. stages.

In video work, proper line termination is as important as proper termination of antenna feeds for TV receivers in order to eliminate ghosting. Mis-match due to improper bridging and termination of lines necessitated serious consideration, for each of the five coaxial distribution lines had an average of twenty different types of receivers on them. Finally, this problem was ironed out and good pictures were received throughout the hall.

Program fare was supplied from three sources, each fed to the input end of the video distribution setup where the switching was made from one source to the next. All TV net-works in New York sanctioned feeds to this show via existing microwave facilities.

WBZ-TV set up a temporary iconoscope camera chain with a 16-mm film projector at the studios and microwaved film shorts to the show. The feature program of the show was a Miss in TV contest put on right at the hall. The WBZ-TV televan, mobile control truck, was set up inside the building to act as a control point for two camera chains on the stage. Each day a group of contestants performed before the cameras, with semi-finals and finals staged at the close of the week.

Station Facilities

WBZ-TV facilities may be sub-divided into four separate groups: the main equipment room, television pro-jection, television equipment and the mobile televan.

Main Equipment Room: In addition to the audio racks and recording machines in the main equipment room. two TV monitor racks, transmitter. side-band filter and diplexer are on the left-hand side, and the FM transmitter with its monitor racks on the right-hand side of the room. The master console for the TV transmitter is mid-way between the two transmitters.

In one of the TV monitor racks are the aural transmitter which contains a sound frequency and modulation monitor program amplifier, and audio monitor amplifier, audio jacks and convenience outlet panel.

The second rack for the video transmitter contains a stabilizing (video line) amplifier, a video carrier frequency meter, an rf patch panel and necessary power supplies to operate the master monitor in the TV console, and the demodulator.

The television transmitter is assembled in eight steel cabinets that contain ihe necessary components of both a video transmitter and a sound transmitter with their associated power supplies and control circuits.

The aural section utilizes an FM exciter, followed by triplers and doublers that drive a power amplifier employing an 8D21 dual tetrode.

The video section employs a standard crystal oscillator followed by a tripler and doublers that drive another 8D21 final amplifier. This stage operates as a grid-modulator power amplifier.

Six 4D27s in parallel modulate the grid of the final amplifier. The video system is a high-gain, three-stage amplifier with excellent frequency and phase response. utilizing a constant resistance network in the anode of the modulator stage. This network makes the internal impedance of the power supply a part of the plate load, thus permitting frequency response down to and including DC. A clamp circuit type of DC restorer is used in the grid circuit of the modulator which clamps on the back porch of the horizontal pulse.

Dual unit reflectometers are included in both the sound and picture output circuits. These units are an invaluable aid in checking and main-taining proper output characteristics.

They perform three main functions:

(1) Measurement of the swr on the main transmission line.
(2) Measurement of the peak of sync power output (when calibrated against the dummy load.)
(3) Operates as an rf overvoltage output, thus protecting the transmission line against rupture due to lightning, bad mistermination or any trouble which causes excessive standing waves to occur.

The output of the picture transmitter is fed into the vestigial side band filter. Physically, this unit consists of a maze of coaxial transmission lines.

Electrically, it comprises a combination of two m-derived filters constructed of low loss coaxial transmission lines. Filter components of the common l-c construction would be difficult to manufacture and uneconomical to use because of the currents, voltages, and reactances involved. Hence, the coaxial Iine construction.

The undesired side band is passed through one of the filter units into a properly terminated transmission line that eliminates reflections of the lower side bands. This termination is in the form of a water-cooled load resistor; its resistance is equal to the characteristic resistance of the line.

The desired signal goes through the second filter and a notch filter. This notch filter is so designed to protect the sound frequency of the lower adjacent TV channel.

Both the aural transmitter and the video output of the side band filter are fed into a diplexer. In a simplified form, the diplexer may be considered to be a balanced bridge circuit in which there are four legs. The visual and the aural signals are fed to alternate diagonals of the bridge. Since the aural signal is fed into the circuit across the mid-points of the antenna and the reactors, no visual signal can go into the aural transmitter. In like manner, the visual signal is fed to the circuit between two points of equal potential with respect to the aural transmitter, so that no aural signal can get back to the visual transmitter.

The two output feeds of the diplexer feed the east-west and the north-south set of the turnstile radiators respectively. In order that a circuit horizontal radiation pattern be achieved, one set of radiators are fed 90 degrees out of phase with the other.

Our transmission line installation departed from that usually installed for television. We used 3 1/8" 51.5-ohm coax but instead of each 20-foot section hung in a suspension type hanger to allow for expansion, our line was secured at two points, one at the top of the tower, the other about half-way down. Immediately below these two points, a coaxial type of expansion joint designed especially for television, was inserted.

The line between these points is held to the tower by loose fitting clamps that allows the line to creep when it expands or contracts with temperature changes.

One thing of particular interest is the matter of suspending the inner conductor in the transmission line. Each 20-foot section has a rolled groove 12” from one end of the line This groove was indented sufficently so that when the line was placed in a vertical plane, the inner conductor insulator would catch on the groove and thereby suspend its own center conductor.

On the horizontal runs, the rolled grooves were alternated to allow for differential expansion. Each length of line was flanged and each piece of inner conductor milled so that the wire conductors could be fitted together with a bullet. The outer conductor flanges were bolted to each other to eliminate the need for any soldered joints in the line.

Should it become essential to cut a piece of coaxial line, it is necessary to solder on another flange but to insure that the line retains a flat characteristic impedance, it is necessary to cut the inner conductor midway between insulators, with the remaining length made up with a special type of inner conductor of slightly larger diameter.

The TV Transmitter Console

The television transmitter console contains three sections: transmitter control, incoming and outgoing program monitors, and three-point video monitoring facilities.

The transmitter control section contains control circuit switches and indicating lights for remote operation of the transmitter. The center section of the console features two master monitors which enable simultaneous checking of the incoming as well as the outgoing program.

The right side of the console possesses a row of push buttons for monitor switching purposes. This system provides for viewing at any one of three points in the system: transmitter input, modulator output and transmitter output.

On this same panel is located another row of buttons for monitoring the signal from reproducers at any one of the foregoing locations. There also are additional controls for monitoring the audio at any of the points in the aural transmitter, as well as a vu meter for indicating audio level.

The wave-form demodulator depicts the amplitude of sync versus video plus overall percentage of video modulation and is observed on a 5-inch CRT mounted in the master monitor. This scope has a variable sweep circuit and by means of a switch, it is possible to observe the vertical field or horizontal line presentation with their associated sync pulse blanking pedestal and video content.

The picture demodulator output is observed on a 10BP4 that is built into the master monitor.

The FM Transmitter

Our FM transmitter consists of three cubicles, the first of which contains a unit for FM modulation and frequency stability circuits. This in turn drives a series of doublers and ends up in a pair of WL 5736s. This particular unit has a self-contained power supply and can be used as a 3-kw FM transmitter as well as the rf driver for the final stage, as we use it.

The center cubicle contains a three-phase rectifier for the final. The third cubicle houses a pair of WL-2500A3s that are air cooled and capable of delivering 10-kw output. It is a grounded grid final employing a form of tuned coaxial cathode and plate tank circuits.
This transmitter is piped into another coaxial line similar to the TV coax installation, which terminates into the two sections of a heavy-duty pylon antenna.

The tower itself rises 572’ above sea level, and the addition of the 2-section FM and 3 bay TV antenna raises the tower to an overall height of 656’.

Television Projection Room

The projection room is located on the first floor, immediately below the TV control room in the southeast corner of the building. It employs two film camera chains employing 1850-A iconoscope tubes, 16-mm film projectors, two 35-mm film projectors with its rack of associated sync light power supplies and picture monitor. There are also three 2 x 2 slide projectors for use with 2 x 2 slides and 35-mm strip film, and one Bal-optican modified to project opaque slides and news tapes.

The 16-mm projectors are used in conjunction with one camera chain, the two 35-mm projectors with the second chain. This is possible by the use of a multiplexer. This multiplexer has two front surface mirrors, enabling each movie projector to be mounted at right angles to the film cameras and the reflected pictures to be focused on the mosaic of the iconoscopes through the front surface mirrors placed on a 45 degree angle.

This system allows greater flexibility of each film camera and simplifies the problem of switching video and sound from one projector to another. This switching is a duty of the projectionist.

There is a film camera control unit for each film camera. These contain a master monitor and a camera control unit that permits individual monitoring of each chain. Controls are readily accessible for shading corrections, a necessary operation with practically every change of scene illumination whether it is film or slide.

In addition, each camera chain requires two heavy duty, regulated power supplies. Four of these power supplies, along with a preamp for the 35-mm machines, fill a second rack in the projection room.

Adjacent to the projection room is a rewind and storage vault for 16 and 35-mm film. Here the film is spliced and edited before gain (sic) on the system.

Television Equipment Room

In reality, the TV equipment room is the overall control point for all types of shows; film, network, studio, and remote. It is a beehive of activity and has gone through several major changes since T-Day. At that time, all of the control room equipment had not yet arrived, so we operated with a temporary setup employing field switching equipment, sync generator, etc. Since that time, a large percentage of our equipment has arrived and has been installed.

Of the six racks, two are devoted to audio. They have jack strips, line amplifiers, monitor amplifiers, and audio line termination facilities for network and remote feeds.

Additional audio facilities include a consolette which permits four studio microphone positions, two turntable positions, and six remote input positions that are wired up for use with the 16-mm projectors, 35-mm projectors, network line, remote lines and speaker monitor for projection room.

Two turntables are used for dubbing in musical background on news shows, sound effects, etc. These tables are equipped with cueing circuits. In addition to this, there are microphones in the studio and announcer’s booth. A large perambulator type mike boom is available for studio shows.

The other racks house video equipment and its associated power supplies. One rack has a master monitor and a rack-mounted switching panel that permits previewing any one of six video feeds on the master monitor, and still another row of buttons with tally lights that are used to feed the transmitter the desired signal. This rack also contains a video patch panel, thereby lending complete flexibility in the event of trouble in any one of the line amplifiers, isolation circuits, etc.

Another rack contains the microwave receiver control unit, isolation amplifiers, a stabilizing amplifier and their power supplies. The microwave receiver operates in the 6,900-mc region. It employs a four-foot parabolic dish and garbage can that is mounted up on the tower. This unit is orientated on remotes being picked up by the televan.

The next rack contains still more isolation amplifiers. They consist of five individual amplifiers, each of which can deliver the same signal level and polarity it receives from a coaxial line (nominally 75 ohms). The inputs are of relatively high impedance so that several can be bridged without disturbing the driving circuit. They are designed to have a band pass from 30 cycles to 8 mc.

Besides acting as isolation amplifiers, they can be used to mix signals whereby the sync pulses are fed into one amplifier, the video with blanking, into another, and the outputs paralleled, with the end result, a complex video signal, complete with sync signals.

A monoscope camera is used to generate the test pattern. At first, we used the standard RMA test pattern embossed on the type 2F21 tubes, but since then have replaced the 2F21 with a tube which has a gridded pattern of horizontal and vertical lines as well as the horizontal and vertical resolution wedges and the call letters WBZ-TV, Boston, Channel 4.

The word garbage can is is well meaning, because it resembles just that form of a disposal can. It is mounted on the rear of the parabolic dish and houses the head end of the microwave receiver. The rf input comes in via a section of wave guide and fed into a crystal mixer. A type 2K26 reflex klystron is used as a local oscillator and beats with the incoming signal to produce an IF frequency of 118 mc. This is amplified in a four-stage IF preamplifier and then fed down to the receiver control unit via RG-8U where it is again amplified and the video component demodulated.

Communications/December, 1948 Sidney V Stadig/Technical Supervisor, WBZ-TV

NOTE: Hotel Bradford located at 275 Trement Street is now the Tremont House Hotel.

Mechanics Building located at 111 Huntington Ave. and the corner of West Newton St. (site of the Prudential Plaza),
built in 1881 at the cost of $500,000. The Grand Hall had a seating capacity for 8,000 people and was home for the
Grand Opera in Boston. There were a number of other exhibition halls. The Massachusetts Charitable Mechanical
Association Building was demolished in 1959. (ggn)