PHILIPS SOZ 182

I. Introduction Recently, Philips Telecommunication Industries delivered to the "Stichting Radio Anno Santo" a short-wave broadcast transmitter which will, in the near future, be installed at Vatican Radio. The carrier output of this transmitter is 100 kW and the frequency range 5.6-26.1 Mc/s (λ = 52 - 11.5 m). The transmitter has been built according to the latest developments and has been provided with an automatic tuning mechanism which allows adjustment within two minutes of the various tuning circuits to any one of six preset frequencies and selection of the corresponding correct voltages, by means of one single frequency-selector switch on the control desk. In addition, manual tuning or correction of tuning is possible without disarranging the preset positions of the instantuners. For automatic frequency selection the small type instantuner 1) is used for the first stages, while a large type 2) is applied in the penultimate and final stages. The large type of instantuner allows of manual correction of the tuning after the desired preset frequency has been selected. This may be necessary, for instance when the feeder impedance changes under the influence of varying weather conditions. However, after a subsequent selection of a preset frequency for which manual correction of one or more of the tuning elements was necessary, the original pre-set position of the tuning elements will be obtained. The units of the transmitter, viz. preceding stages, final stage, modulator, power supply, distribution panel, high-voltage rectifier etc., are mounted in separate frames which are placed behind a "dead front" provided with doors. On the upper part of this front is a metering panel. The transmitter is controlled and supervised from the control desk which is placed in front of the transmitter. As a result of the simplicity of the manipulations, only a few minutes are required for changing over from one preset-frequency to another. Since the transmitter consists of separate units, various arrangements are possible which allow a suitable lay-out for almost any kind of transmitter building. The standard arrangement is shown in fig. 1, while fig. 2 shows a model of the transmitter. In the completed transmitter, the various frames form one screened unit so that interference due to direct radiation has been reduced to a minimum. In order to obtain a pleasing appearance, the transmitter is placed behind a front panel provided with doors. Access to the tuning knobs and the supervisory instruments can be obtained via doors. The attending personnel is safeguarded by means of an interlocking system which meets the most stringent requirements. High voltages are automatically switched off when the door in front of the particular high-voltage unit is opened, and high-voltage charges on condensers are short-circuited by means of earthing switches. Al d-c voltages up to 1000 volts are supplied by means of selenium rectifiers; the 3000 volts suply is obtained by means of a valve rectifier, and the 10 kV voltage for the modulator, the penultimate and the final H.F. stage is supplied by means of a mercury-steel rectifier. When the water pipes for the cooling system, and the cables for the interconnection of the various units, are mounted in a cable duct, a cellar is not necessary. The transmitter has been designed so that reliable operation is obtained under widely varying climatic conditions. Where necessary, components are heavily silver-plated. A special oscillator is provided to obtain a very high degree of stability on each preset frequency. Fig. 3 shows the block diagram to which the reader is referred in connection with the detailed description of the transmitter that will now be given.

II. The exciter unit For each of the six preset frequencies a separate exciter channel has been provided; in addition, two spare channels are available. The temperature variation of the crystal of each exciter channel is kept within narrow limits by means of a thermostat. The operating frequency of the crystal has been kept low and varies between 0.25 and 0.9 Mc/s. After a frequency multiplication of eight times in the exciter channels, an operating frequency between 2 and 7.2 Mc/s is thus obtained. The eight exciter channels are mounted in one rack (HF1) which can be placed anywhere in the transmitter building. The common last stage of all exciters (the input amplifier of HF II) is not placed in this rack but in the cabinet for HF II-V. Each exciter channel consists of a crystal-sontrolled oscillator of special design, three frequency-doubler stages and the inut amplifier of HF II already mentioned. To allow continuous operation of one or more of the exciter channels (in order to increase the frequency stability), three (or if required, four) channels can be fed by a separate power supply, independent of the power supply for the transmitter proper. Each oscillator with its succeeding stages is mounted on a separate chassis that can easily be slid into the rack. The connections between the various stages are obtained by means of plugs. Fig. 4 shows the rack with 8 exciter channels, two of which serve as spare channels or may be used for an extra transmitting frequency. This rack has not especially been designed for the 100 kW transmitter but will be used for any shortwave broadcast transmitter for which more than one frequency range and a high degree of stability are required. In the lower part of fig. 4 the eight amplifiers are shown. As a rule, these amplifiers are mounted in HF II, for in case of emergency, or as a spare, each of the input amplifiers in the HF II-cabinet can be replaced by an oscillator (with its corresponding amplifier) of simple design, and with a frequency stability much less than that of the normal exciters. In fig. 5 the normal in put amplifiers have been replaced by these emergency (spare-) oscillators, the former being placed in the rack HF I (fig. 4). As a rule, however, the emergency (spare-) oscillators are mounted in HF I where in fig. 4 the input amplifiers, which are not in use there, are visible. After initial adjustment of the tuning elements, one of six of the eight available preset frequencies of this 100 kW transmitter can be selected automatically. The remaining two frequencies can be adjusted manually. The desired operating frequency can be selected by means of a switch controlling an instantuner. The selector switch is mounted in HF II (following the input amplifiers).

III. The preceding stages The rack HF I with the exciter channels is followed by a cabinet (fig. 5 and 7) in which the amplifier and frequency doubler stages HF II, III and IV are mounted. The frequency of the input signal lies between 2 and 7.2 Mc/s. HF II operates either as an amplifier or as a frequency doubler, whereas HF III always operates as a frequency doubler. HF IV and HF V are high-frequency push-pull amplifier stages and are both tuned to the ultimate operating frequency. The six input amplifiers are placed in the lower part of the cabinet (fig. 5). The high-frequency stages HF II-V mounted together in one chassis which is supported by means of telescopic mountings. In fig. 5 this chassis is shown partially extended. The tuning elements of these stages and the frequency-selector switch which is mounted on this panel, are operated by instantuners. The 2 kW HF stage V is mounted behind a separate panel, in the upper part of the cabinet. This stage consists of a push-pull class-C amplifier with two Philips' pentodes, type PB 3/800, the anode voltage being 2500 V. The anode tuning circuit and the inductive coupling with the succeeding stage are similar to those of the 40 kW transmitter 3). Behind the panel of HF V are mounted three instantuners for the automatic frequency selection. The control knobs are visible in fig. 5, while fig. 6 shows the instantuners (frontpanel of HF V removed), the anode circuit of HF V being partially visible. In fig. 7 a rear view of the frame is given in which the anode circuit HF V is clearly shown. In the same figure the rectifier for the oscillators normally in use, and for the corresponding input amplifiers, is visible (fig. 7 below). On the front of the cabinet (see fig. 5) are mounted the meters for checking the grid currents, anode currents, etc., and various switches which can also be actuated when the door is closed.

IV. Driver, output stage, filter for the suppression of HF-harmonies, and artificial aerial 1. Driver stage To the 2 kW high-frequeney stage V deseribed above is coupled the driver stage HF VI which provides the excitation energy for HF VII. This driver stage, together with the final stage, the filter for suppressing harmonics, and the artificial aerial, forms one unit. In order to facilitate production and transport, this unit has been divided into various sections, viz. one section containing the complete driver stage: a unit which adjoins the driver-stage section and contains the grid circuit with the valve arrangement of the final stage; a unit with the anode circuit of the final stage; a frame containing the above-mentioned filter and the feeder-selector switch: and finally a frame for the artificial aerial. These units are all placed behind a single front panel which is provided with two doors giving access to the various sections, in order to allow tuning and supervision. Fig. 8 gives a simplified circuit diagram in which those tuning elements that can be selected by their instantuners, after having been preset, are marked I. The output of the driver stage, which operates with two water-cooled triodes, type TAW 12/10, in push-pull, is approx. 10 kW. The grid circuit of this stage has been designed for three frequency ranges and consists of a circular Lecher system L, which, for the upper frequency range, can be tuned by means of a movable short-circuiting bar. For the middle frequency range a fixed condenser can be switched between the grids of the valves, which results in an electrical extension of the Lecher system. For the lowest frequeny range a larger fixed condenser is switched to the Lecher system. The inductive coupling between the Lecher system L1 and the preceding stage is variable. Fig. 9 gives a rear view of HF VI (covers removed); at the right, the folded Lecher system is visible. As in the 40 kW transmitter, triple contacts have been applied for tuning the Lecher system and for switching the various condensers 3). These triple contacts are fitted to two ceramic rods which rotate on a shaft mounted in the centre of the circular Lecher system. By rotating the shaft, a movable short-circuit is obtained. On this shaft can also be rotated the loop for the variable coupling with the preceding stage HF V. These tuning elements are driven by means of the respective instantuners which are mounted at the front of the particular cabinet section. The control units of these instantuners can be seen in fig. 10. At the upper left (fig. 10) are mounted the switches for selecting the high voltage corresponding with the various operating frequencies, selection of the correct high voltage being necessary in order to ensure correct operation of the valves in the output stage. At the right, the instantuner for tuning the anode circuit can be seen. The anode circuit of the driver stage has been designed for two frequency ranges and consists of a combination of one fixed condenser and two variable inductors (L2 and L3). For the upper frequency range the tuning capacity is formed by the inter-electrode capacities of the transmitting valves and by the stray capacity of the coils etc., whereas for the lower frequency range a fixed vacuum condenser is switched into the circuit. The type of coil used in this stage is of similar design as that of the coils used in the anode circuit of the output stage of the 40 kW transmitter 3). However, the excitation of the output stage of the 100 kW transmitter is obtained by means of a capacitive tap on the coil L2. The neutralizing condenser is formed by the jacket of the valve holder which has the same potential as the anode of the valve, and by a cylindrical jacket which has been placed concentrically with respect to the jacket of the valve holder. Part of this outer jacket is hinged; by varying the position of this part the neutralizing capacity can be varied. The outer electrodes of the neutralizing condensers are connected to the grids of the valves in a special way by means of straps. As a result of a balanced construction, both electrically and mechanically, of the jacket of the neutralizing condenser, it is possible to maintain one position of the hinged section throughout the frequency range of 5.6 Mc/s to 26.1 Mc/s. Fig. 11 shows the neutralizing condenser and, in addition, the gland nut with which the valve is fastened to the cooler. The method used for fastening the valves to the coolers allows for rapid replacement. To improve the accessibility, the horizontal mounting plate with various decoupling condensers can be turned upwards. In fig. 11 (at the left) a raised mounting plate can be seen behind the valve. The same figure also shows the switch contacts for connecting the fixed condensers across the Lecher system (the condensers are not visible in the figure). As mentioned before, all essential components, such as the Lecher system with its contacts, the anode circuits with contacts etc., are heavily silver-plated. Fig. 9 shows the HF stage VI, mounted in its frame, as a separate unit. At the upper left, the lever of the earthing switch, which can also be operated at the frontpanel, can be seen. This switch must be placed in the "earth" position before the screen plates can be removed to obtain access to the inner part of this stage. By means of this switch dangerous voltages are switched off, and the condensers are discharged and connected to earth. The transmitting valves are cooled via the anode tuning coil. The inlet and outlet nipples for the cooling water are mounted at the centre trap of the coil. The high-frequency voltage drop across the resistance formed by the cooling water can then be practically neglected, so that the influence of this resistance as a variable tuning element is nihil. The supply pipe and the outlet pipe for the cooling water are made of polyvinylchloride, and insulating material, the softening temperature of which is above 110 degrees centigrade.

2. Grid circuit of the output stage As already stated, the cabinet of the high-power modulated output stage (HF VII) is placed next to the 10 kW stage. The output stage is built in two separate cabinets. The frame adjoining the 10 kW stage contains a similar Lecher system (L4, fig. 12) to that in the preceding stáge (fig. 8). As a result of the large input capacity of the 100 kW transmitting valves which are mounted in this frame, this grid circuit has also been designed for three frequency ranges. This is obtained by electrically shorting or extending the Lecher bars. For the middle frequency range the ends of the Lecher bars are short-circuited by means of a movable short-circuiting bridge. For the upper frequency range the short-circuiting bridge is replaced by fixed condensers which, for the two lower frequency ranges, are shorted by means of contacts driven by a servo-motor. The lowest frequency range is obtained by connecting fixed condensers between the grids of the transmitting valves. Except for the servo-mechanism the construction of this grid circuit is the same as that of the 10 kW stage. In the output stage two water-cooled triodes, type TBW 12/100, are connected in push-pull, anode modulation being applied. Neutralizing takes place in the same way as described for the 10 kW stage. Here too, the position of the adjustable section of the neutralizing condenser remains unaltered throughout the entire frequency range. Application of the Grip-O-Matic cooler 4) allows the large transmitting valves to be replaced within a few minutes so that the time of interruption of a program as a result of a faulty valve can be very short. The unit is illustrated in fig. 12. On the foreground to the left the variable sections of the neutralizing condensers can be somewhat higher the fixed condensers for the lower frequency range are visible. The single-phase filaments are heated by a—c current, the transformers being mounted immediately above the transmitting valves. In order to prevent access to parts carrying dangerous voltages, an interlocking system has been used which is analogous to that used in the 10 kW stage.

3. Anode circuit of the final stage The anode circuit of the final stage is mounted in a separate frame placed adjacent to the preceding frame (fig. 13). For the anode-circuit tuning, use has also been made of a Lecher system (L5 of fig. 7), the length of which can be varied by means of a short-circuiting bridge. Here too, the electrical length of the Lecher system can be extended by switching fixed condensers into the circuit. The anode-Lecher system consists of two circular flat copper strips between which the short-circuiting bridge can be moved. At one extremity, the strips of the Lecher system are permanently connected together. Via this connection the modulated anode voltage is fed to the anode circuit. The anode voltages for the various frequeney ranges are 10 kV for the range 5.6 to 20 Mc/s; 9 kV for the range 20 to 25 Mc/s; and 8.5 kV for the frequeney range 25-26.1 Mc/s. For this reason the primary winding of the high-voltage rectifier supply transformer is provided with taps. During selection of the required tap by means of a switch driven by a servo-mechanism, the power is switched off. Since the required high-voltage depends on the operating frequency, it can be preset on the afore-mentioned panel of the 10 kW stage (see Ch. IV, 1) during the initial adjustment of the various preset frequencies. One of the strips of the Lecher system is used as a contact surface for the short-circuiting bridge; rectangular cross-sections have been chosen in order to keep the characteristic impedance of the Lecher system as low as possible. Nothwithstanding the relatively large interelectrode capacities and the stray capacities of the neutralizing condensers etc., still a wide tuning range has thus been obtained. Tuning at the lower frequency ranges is achieved by connecting fixed condensers in the anode circuit, in two steps. In order to safeguard the short-circuiting bridge of the Lecher system against excessive temperatures, which would occur as a result of the large high-frequency currents flowing under normal conditions, the contacts of this bridge are cooled. As in the 10 kW stage, sections of the inlet and outlet pipes of the cooling water are made of polyvinylchloride insulating tube, because of its high melting temperature. The coupling with the feeder, or in this ease with the harmonie-suppression filter, is formed by a hairpin-shaped coupling link the position of which can be varied by means of an instantuner. The Lecher system of the anode circuit and the corresponding movable coupling link are shown in fig. 13. 4. Filet for the suppresion of HF harmonics In the Vatican transmitter the output stage is followed by a filter which suppresses the harmonics of the operating frequency. As is illustrated in fig. 8, this filter consists of a π-section which is symmetrical with respect to earth. Both the input and the output condensers are variable, while fixed condensers can be connected in parallel for the lower frequency ranges. The coil of the π-filter is provided with taps which are selected in accordance with the various frequency ranges. This unit too, together with a feeder change-over switch, has been placed in a cabinet. The switch allows easy matching of the artificial-aerial impedance to that of the feeder. 5. Artificial aerial The artificial aerial which is also mounted in a separate cabinet, consists of twelve water-cooled resistors. With the aid of a direct-reading thermometer (or mercury thermometer) and a water-flow meter, the energy dissipated by the artificial aerial can easily be calculated. The artificial aerial is illustrated in fig. 14.

V. The modulator The energy for modulating the high-frequency output stage is supplied by an AF amplifier, the final stage of which operates with the same type of valves (viz. TBW 12/100) as are used in the high-frequency output stage. In fig. 3, a block diagram of the AF amplifier is given, showing that the AF signal is fed to the submodulator via an H-attenuator mounted on the control desk. By means of various AF stages this signal is amplified up to the required level. For a modulation depth of 100 percent the input-signal voltage must be adjusted to 1.5 volts RMS across a characteristic impedance of 600 ohms, by means of the H-attenuator. The stages M I and M II are resistance-coupled amplifiers in push-pull. The coupling between the stages M III and M IV is formed by a cathode follower, the advantages of this coupling method being well-known 3). The complete modulator (M I-IV) is mounted in a single cabinet, except for the modulation transformer, the modulation choke and the associated decoupling condenser which are placed in a high-voltage compartment. For the sub-modulator (M I-III), panel mounting is used, affording direct access to the valves, after opening the door at the left side of the frame (fig. 15). This facilitates the replacement of a valve. All dangerous voltages are cut off by means of door-contacts, and the condensers are discharged to earth when a door is opened. The panel on which the submodulator stages are mounted is hinged and can be pivoted on a vertical axis, so that the rear of this panel (see fig. 16) is easily accessible for inspection. Fig. 16 also shows the blower which provides a slight air flow for the valves, type PB 3/800, in case of tropical operating conditions. The cabinet containing the valves of the push-pull output stage of the modulator which uses valves, type TBW 12/100, in class B, is placed next to the submodulator.

The valve complement comprises three valves, two of which normally are in operation while the third is used as a spare valve. This is shown in fig. 17 (the valve in the left section has been removed). Change-over switches, controlled by one handle, allow the spare valve to be placed in circuit during operation within one minute. Interruption of a program as a result of a faulty valve is thus limited to only a few minutes. The change-over switches are controlled by a handle, visible on the foreground of fig. 17. By pushing this handle forward, all high voltages are automatically switched off and all condensers shorted. In this position, the handle can be rotated through an angle of 2 x 90°. The position of the handle shown in fig. 17 corresponds with the left valve and the centre valve in operation. After the handle has been pushed inward and rotated through an angle of 90°, and then pulled out, the two outer valves are ready for operation. By rotating the handle through an angle of 180° instead of 90°, the right and the centre valves are ready for operation. When a valve must be replaced, the handle must be pushed inward which results, as already mentioned, in switching off dangerous voltages and removal of the charges on the condensers. After the manipulation, a locking mechanism must be loosened to allow the removal of the screenplates in front of the valve to be replaced. After that, the cradle of the valve can be tilted (figs. 17 and 18). Since in this stage too, the Grip-O-Matic cooler is applied, replacement of a valve is reduced to a very simple manipulation. Fig. 18 shows the valve arrangement; the cradle of the valve holder is tilted and all is ready for replacement of the valve. In this figure are also visible the change-over contacts of the anode (partially shown).

VII. Cooling In order to reduce corrosion, the closed cooling system for the transmitting valves TAW 12/10 and TBW 12/100 is operated with distilled water. Moreover, thoughout the cooling system, copper pipes, copper accessories and bronze conical fittings, joining the various pipes, prevent electrolysis. After passing the cooling jackets of the valves, the water is fed to a radiator cooled by a blower. The blower, the water-circulation pump, the water tank and the auxiliary apparatus are combined in a single unit which greatly facilitates the assembly and the supervision during operation. Fig. 19 gives an illustration of this cooling unit.

TECHNICAL SPECIFICATIONS
Frequency	The frequency range is from 5.6 Mc/s to 26.1 Mc/s. Within this band, six preset frequencies can be automatically reset by means of a frequency-selector switch.
Power	Throughout the entire frequency band of 5.6 Mc/s to 20 Mc/s the power output amounts to 100 kW; from 20 Mc/s upwards to 26.1 Mc/s the output decreases to 70 kW.
Matching	The transmitter can be matched to a symmetrical open wire feeder having a characteristic impedance between 300 and 800 ohms.
Mains supply	The mains voltage for the anode supply of the stages HF VI, HF VII and M IV is 3 x 10000 V, 50 c/s, while for all other equipment 3 x 380 V, 50 c/s with neutral wire is used. In order to ensure correct operation, voltage fluctuations and frequency variations of the mains supply must not exceed ± 5 percent.
Frequency stability	When taking into account the following stipulations, the maximum frequency deviation with respect to the operating frequeny will not exceed ± 20 c/s: 1. mains voltage fluctuations may not exceed ± 5 percent: 2. ambient temperature may not exceed 40 degrees centigrade; 3. the stable oscillators must be operated continuously.
Attenuation distortion	In fig. 20 the attenuation distortion for an operating frequency of 12 Mc/s is plotted versus the frequency of a sinusoidal AF modulation input signal, the amplitude of which corresponds to a modulation depth of 80 percent.
Non-linear distortion	The non-linear distortion for an operating frequency of 12 Mc/s is given in Table I.
Hum level	The hum level is better than -56 db, a modulation depth of 100 percent being taken as reference.
Power consumption	For an operating frequency of 12 Mc/s the power consumption is given in Table II.
High-frequency harmonics	Since no generally accepted and reliable method for measuring harmonic frequencies of a transmitter under operation is known, the following procedure has been followed. By means of a standard-signal generator a continuous high-frequency voltage is fed to the anode of one of the valves of the output stage. When the voltage of the signal occurring at the input of the artificial aerial is then measured, the attenuation of the filter, combined with the anode circuit, can be determined, for the operating frequency as well as for a number of specified harmonic frequencies. For an operating frequency of the filter of 16 Mc/s the attenuation of signals having a frequency of 32 Mc/s and of singals having a frequency of 48 Mc/s is 48.5 db and 50.7 db respectively, the attenuation of the operating frequency of 16 Mc/s being taken as a reference.

THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES
	ITU	Country		ITU	Country
	CVA	VATICAN CITY