SHUM-5A TV transmitter
Vladimir Zaytsev, Nikolay Tihonov, Leonid Shumakov

Shum TV transmitter of IV...V TV bands, the third one in the powerful klystron transmitters series, has 5/0,5 kW output power. A distinctive feature of the transmitter is separate amplification of display and accompanying sound signals.

The transmitter contains:

• exciter;
• display signal output power amplifier (OPA);
• sound signal power amplifier (SPA);
• cooler with air pipes set;
• CTC3-25 alternating voltage stabilizer.

The transmitter's radio frequency channel consists of three main parts: exciter, display signal output power amplifier with diplexer, and sound signal power amplifier (see the scheme). The exciter employs Sigma-D TV modulator (3 units), which has proved itself in exploitation. Operation OPA and SPA is provided by a pair of inter-reserving TM1 and TM2 modulators, having separate outputs and output power in clock pulse peak of about 1 mW, and by a commutation and amplification block (CAB), containing four-channel amplifier within 30 dB channel amplification. Each amplifier's channel is designed on the basis of Hella micro scheme of the Mini-Circuits company manufacture. TM3 modulator gives the summated TV signal with output power in clock pulse peak of up to 50 mW and is switched on when reservation of the display signal OPA is necessary.

TV transmitter "SHUM-5A"

The klystron has three main advantages:

• power amplification factor is not less than 40 dB;
• electronic performance factor is 55...60%;
• warranty life is 10,000 h.

These very klystron's advantages contribute to simple design of the reliable and economical single-stage OPA. Input circuit of the OPA is connected to the commutation and amplification block's commutable output and contains a stepwise-regulated 0...4, 10 dB attenuator and isolation valve. Input display radio signal power equals 1 W. OPA's output circuit contains a circulator (with real loss not more than 0,3 dB) with ballast load of 200 W, as well as directional couplers, diplexer (i.e. separation filter), and 2 x 2 antenna switch. Directional coupler's signals are used for measuring the transmitter's output power, for control of the standing-wave ratio in HF channel and of the "OPA - exciter" feedback path's operating. Antenna switch allows turning the transmitter on artificial antenna. The OPA does not have harmonic filter because levels of the third and the second harmonics of display signal at the klystron's output do not exceed -30 and 35 dB respectively, being decreased to 30 and more dB by the circulator.

Serial Onega-1 transistor TV transmitter of 1/0.1 kW, without exciter, with small modifications, is used as SPA. It provides sound signal output power of 650 W, with commutation and amplification block's input signal being not more than 50 mW. SPA has module design allowing reservation mode where SPA operates with reduced output power if any finite module falls out.

Power-amplified 5.5 kW display signals and 0.65 kW sound signals are summated in the diplexer. The diplexer's design is formed by star connection of the filters. One of these filters sends display signal with 30 dB rejection of the nearest to sub-carrier spurious signal, the other sending accompanying sound signal.

Diplexer has the following performance specification:

• loss in display signal carrier frequency is not more than 0.3 dB;
• loss in accompanying sound signal carrier frequency is not more than 1.0 dB;
• coupling loss in display signal carrier frequency is not less than 35 dB;
• coupling loss in accompanying sound signal carrier frequency is not less than 25 dB.

In the event of OPA's falling out SPA is used as usual TV transmitter with common display and sound signal amplification and output power in clock pulse peak of 1 kW. In such case TM3 modulator is connected to the transmitter's input instead of TM1 or TM2 modulators, and TM3 output summated signal is sent to SPA, which is switched in the joint amplification mode. SPA's output is connected directly to antenna switcher instead of diplexer.

OPA and SPA have separate control, block and alarm system (CBA) that is multifunctional. It provides:

• executing necessary operations under compulsory sequence of the klystron's feeding voltages on/off;
• switching off feeding voltages under transistors current overload, rise of the klystron and transistors' acceptable operating temperature, rise of the standing-wave ratio in HF channel over acceptable value, fall of pressure in the klystron's collector cooling air-pipe;
• operation of circuits locking the access to high-voltage modules of the transmitter when it is turned on.

Primary power supply system includes stabilizer of 380 V, 50 Hz three-phase alternating voltage of CTC3-25 type, main automatic switches of OPA and SPA power, contactors, relays and safety devices are supplied by the consumers.

Power-feed circuit of high-voltage OPA's rectifier contains mechanic block isolator, phased current sensors, and contactors, providing (under the transmitter's regular exploitation conditions) two-stage switching of the rectifier and the klystron's operating in training conditions with low rectified voltage. OPA rack's alternating voltage is sent to its external consumers - cooler and artificial antenna - through individual automatic switches.

Power used by the transmitters from main power supply equals 19 kW; SPA's part is 3,5 kW, and it may be considerably reduced at the expense of its operating mode optimization. In the system of secondary power supply, the main power consumer is the klystron. The klystron's functioning is provided by:

• high-voltage rectifier with single-mess LC-filter (9 kW, 1.35 A);
• klystron beam focusing solenoid's power supply with load current stabilization (100 V, 11 A);
• klystron heat power supply (6.3 V, 8 A);
• klystron electric-discharge pump power supply (3.5 kW, 10-3 mA).

The OPA's control, block, and alarm system (CBA) feeds from MIP 125 CM-27 B power supply. SPA may use three types of power feeders of 5...27 V. TM1...TM3 TV modulators in the exciter have independent low-voltage power feeders. KN50-L-type power feeders of 12 V send voltage onto the CAB amplifiers..

Control system allows automatic and visual monitoring of the operation mode of the whole transmitter and of its components. Monitoring is made by means of pointer indicators, solid-state lamps, current, temperature and pressure sensors.

OPA rack and SPA frame have independent air cooling. The air is brought in from the workroom. OPA employs an exhaust cooling system, providing necessary thermal conditions for the klystron's operation. Output HF signal excluded, dissipated power on the klystron's collector makes 12 kW in static mode. This power is taken off with the help of FS-3000 cooler having productivity of not less than 1,200 m3/h with pressure differential of about 150 mm lift. The temperature of the collector's hottest area makes about 160°C in the klystron's static operation mode and 100°C in the dynamic one. The superheat temperature of the OPA rack's cooling air is not more than 30°C. Before a portion of airflow reaches the collector's air pipe, it cools the klystron beam focusing solenoid, the solenoid's power feeder, and the high-voltage rectifier's components. SPA employs separate amplifier cooling with the help of 1.25eV-2,8-6 electric air-exhausting coolers, set in the blocks and equipped with air-pipes.

Constructively, the transmitter consists of four blocks:

• OPA rack;
• spa frame with exciter;
• cooler;
• alternating current stabilizer.

Block-scheme of RF-tract of transmitter "SHUM-5A"

SPA rack has a block design and contains four functionally completed blocks. Monitoring, control, and indication elements are located on the blocks' front panels. SPA's HF-connections are provided by a radio frequency cable and, partially, by a rigid 35/10 mm coaxial feeder (in output). The SPA is connected to diplexer in HF-channel by PK 75-17-22 OPA cable.

The exciter contained in three TV modulators and CBA is placed in the bottom part of the SPA rack.

Cooler is placed in immediate proximity to the OPA's rack. Stabilizer's placement is not strictly regulated. The transmitter's weight is about 900 kg.

In conclusion, it is necessary to stress once again that the klystron-based transmitter with in-built resonator, in the developers and manufacturers' opinion, possesses an optimal set of exploitation characteristics. Its main advantages, proved by long experience, are utmost simplicity and reliability in exploitation. As for power consumption it ranks among most economical - like tube transmitters - and are not inferior to transistor transmitters.

Provided by Signal Company.

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