RCA BHF-10A

GENERAL DESCRIPTION


H.F. BROADCAST TRANSMITTER, BHF-10A - 10 KW HIGH FREQUENCY BROADCAST TRANSMITTER

photo RCA BHF-10A FEATURES DESCRIPTION

The BHF-10A transmitter combines all the best features and accumulated knowledge of 25 years experience in the design, manufacture and operation of broadcast and high frequency transmitters. The four main cabinets, and external plate transformer contain all the elements functionally disposed to deliver a fine quality broadcast signal to a high frequency radiating system within a short time after unpacking and placement. The only building arrangements required prior to installation are (1) a floor area suitable for the load, (2) incoming power and program service and (3) outgoing radio frequency transmission lines.

Power Circuits

The right hand cabinet houses power circuits and the electronically controlled main rectifier utilizinq 4 high power mercury vapor thyratrons, type 5563. Electronic control coordinates several functions (heretofore handled with cumbersome magnetic devices) into a smoothly operating system with the selective safety and back up protection using a sturdy contactor and a high speed breaker.

Low Power Circuits

The right center cabinet houses intermediate voltage, direct current power supplies; the primary radio frequency source (an external frequency source may be used) and intermediate radio frequency amplifiers. Five crystal positions are available for instant selection with a 5 position switch. Buffer stages are integral with the frequency source unit which also contains its own direct current power supply. The two intermediate amplifiers, one 6146 and three 813's, provide stable, high gain amplification with ample output for driving the power amplifier.

Power Amplifier

Next in line to the left is the radio frequency power amplifier cabinet with two screen grid, type 6166, air cooled tubes. Use of this tetrode type tube provides a great advantage in highest power gain with stable operation. Elimination of neutralizing circuits is a further advantage resulting in fewer components subject to failure and reduction of power wasting and excessive radio frequency currents at the higher operating frequencies.

Output Circuits

Impedance matching of power amplifier output to transmission line along with harmonic attenuation is provided by a variable network. This circuit allows adjustment during operation to maintain constant output for variations of 10% from normal load impedance.

Modulator

The left hand cabinet contains all tubes and circuits associated with the Class B modulator. Program input is raised from a 10 milliwatt level to 6500 watts needed to modulate the power amplifier. Low power push pull stages include two voltage amplifiers and a cathode follower. Output from the two air cooled modulator tubes is coupled to the power amplifier through the familiar transformer-reactor combination. Approximately 20 db of feedback is applied from the modulator plates through a simple network to the grids of the input amplifier.

Integral Auxiliaries

All heavier components (plate transformer excepted) such as filament and intermediate power transformers, filters, modulation transformer and reactor, blower and filters are housed in the lower sections of the four cabinets. Front and rear, light weight, aluminum panels are quickly removable by hand for full accessibility to any of these components. Two finger operated locking lugs secure each panel. These lugs are accessible only after opening the corresponding upper section sliding door so that it is impossible for personnel to expose any high voltage circuits without first opening a door which operates interlock and grounding switches.

Floor Space

The four cabinets occupy a floor space of 11 feet 1 inch (340 cms.) front and rear by 2 feet 8 1/2 inches (82.5 cms.) deep. The plate transformer which can be located where most convenient requires a floor space of 19 x 24 inches (49 x 64 cms.). Wire ducts are provided to run the inter connections between this transformer and the power supply cabinet.

Optional Supervisory Console

BTC-1A Universal Transmitter Console, MI-28950. This unit can be supplied where it is desired to combine program control functions and essential transmitter controls from a single location in front of the transmitter.

Other Accessories

The RCA International Division can supply spare parts, program speech input cabinets, local studio equipment, measuring equipment, transmission lines, antennas, emergency power supplies and other items to equip a transmitter plant as a completely integrated installation.

RCA BHF-10A diagram

TECHNICAL SPECIFICATIONS
Type of Emission A 3
Output Frequency Range 3.2 to 26.1 mcs
Power Output at Transmitter terminals 10 kw unmodulated
Output Load Impedance 350 to 650 ohms resistive ±JO.1R
Radio Frequency Harmonic Output Less than 200 milliwatts
Frequency Stability 0.003%
Type of Modulation High level, Class B
Program Input Impedance 150 or 600 ohms
Program Input Level (100% Modulation) +10 dbm ±2 db
Audio Frequency Response ±1.0 db 50 to 7,500 cycles
±2.0 db 30 to 10,000 cycles
Audio Frequency Distortion (at 95% Modulation, 50 to 5,000 cycles) 4.0% RMS maximum
Noise Level, Unweighted (below 100% Modulation) 54 db
Carrier Regulation Less than 5% up to 100% modulation
Power Consumption
 Without Modulation
 40% Modulation
 100% Modulation
22 kw approx.
28 kw approx.
35 kw approx.
Power Factor .85
Power Line Requirements 230 volts, 3 phase, 3 wire, 50 cycles
Permissible Power Line Regulation 5% zero to full load
Permissible Power Line Combined Regulation and Variation Limits ±5%
Ambient Temperature +45 degrees C max.
Elevation 8000 feet max.
Frequency Change Time
 (a) 4 to 22 Megacycle Range
 (b) Range (a) to 26.1 or 3.2 Megacycle Ranges
120 seconds max.
300 seconds max.
Specifications may change without notice

TUBE COMPLEMENT
RF stages AF stages and modulator Rectifiers
Number Type Number Type Number Type
2 6166 2 5762 4 5563
3 813 4 813 4 8008
1 6146 2 828 1 2D21


2 807



THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES

ITU Country
ITU Country