24/10/2017
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Engineering and Science>Communication >
VHF / FM Transmitters up to 2 KW

VHF/FM Broadcast Transmitters

 

 JDFM1000 is an air-cooled, fully solid-state FM transmitter with 1kW output power. It consists up of four main building blocks including RF block, exciter block, control block and power supplies.

 


These building blocks are arranged in the following 19" units:

FM Exciters (and MCU)

Change-over (for Exciters) and Rack Memory

Power Combiner

RF Power Modules


 

RF Block

 Two independent 600 watts amplifier modules are fed with input RF from a 2-way power divider. After 33dB gain in power modules, they are combined in the power combiner unit to make 1200 watts RF output power, sampled by the directional coupler and fed to the antenna system. The output sample is used by MCU (monitoring & control unit) for several measurements like forward and reflect powers. Power amplifier modules include: 15 watts RF driver, 3-way power splitter and combiner, three MOSFET-based amplifier circuits, harmonic filter, high and low voltage DC power supplies, APC board (automatic power control) and cooling fans.

 


Dual Exciter System

Two separate exciter units and a change-over unit are in this block. Operation status of the transmitter is programmed by active exciter and saved in the rack memory. When the exciters are changed manually (or automatically in a fault condition), all the current settings of the transmitter are downloaded from the rack memory to the other stand-by exciter via intelligent change-over unit, and system starts up at the same situation.


The building blocks of an exciter unit are: – Audio processing unit including built-in stereo encoder – PLL synthesizer with 10 KHz minimum frequency steps – RF pre-amplifier – MCU (central monitoring and control of the transmitter) – RDS encoder (optional)

 

 

 

1KW FM Transmitter Features

- Redundancy 600 Watts RF Amplifier ×2
- Protection VSWR (With Recycle algorithm), High Temperature, Power Supply Fail, RF Loop connection
- Audio Input Mono, Stereo, Composite Signal (R, L, MPX)
- Broad Band , Adjustable Bias Power Modules
- Dual Exciter System (main & stand by) with manual and automatic change-over increases the transmitter reliability to be on-air in fault conditions
- Rack Memory System saves the current settings of the transmitter automatically which is downloadable by the replaced exciter after changing-over process
- Hot PLUG-IN Design
- RDS Option Improved
- I²C-BUS serial protocol for data transferring

 

1KW FM Transmitter Technical Specifications

Frequency range:
88MHz-108MHz, programmable in 10 KHz/100KHz steps (no tuning)

Harmonic/spurious output :
Meets or exceeds FCC, CCIR requirements.

Asynchronous AM S/N Ratio:
Better than 55dB below rated power reference carrier with 100% AM modulation at 1 KHz, 50µsec
de-emphasis (no FM modulation present)

Synchronous AM S/N Ratio:
Better than 50dB below rated power reference carrier with 100% AM modulation at 1 KHz, 50µsec
de-emphasis (with FM modulation ±75KHz)

FM S/N ratio:
Better than 65dB

Stereo separation:
Better than 40dB

Audio Input level:
-10dBm to 10dBm

Audio Input connectors:
XLR 600Ω/10KΩ balance

External MPX input signal

Open and short circuit protected

PA & Combiner high temperature protection.

VSWR protection
1.5 to 2:1 output VSWR: Automatic power reduction
>2:1 output VSWR: Shutting down during a recycle process

Efficiency:
60% typical DC to RF

RF output power ratings:
Up to 1200 watts

RF output connector:
7/16 inch female


 

 

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