Brookdale ATV Repeater System Information

block diagram

The Brookdale ATV Repeater System is comprised of several sub-systems that are interconnected to form a complete 70-cm in-band repeater system. All sub-systems are contained within a single 19-inch equipment rack.

The repeater receives incoming NTSC video signals on a video carrier frequency of 426.250 MHz using a horizontally polarized, omni-directional, WB0QCD Alford-Slot antenna system mounted atop a 350 foot radio tower. The antenna is connected to the repeater system electronics through a 390 foot length of Celwave model FLC 78-50J 7/8-inch foam-filled Cellflex hardline. A TX/RX Systems model 26-66-01A combline duplexer allows both the receiver and transmitter functions of the repeater to share a common feedline and antenna system.

Received signals passed through the duplexer are further filtered through an International Crystal Manufacturing (ICM) model FL407 7-pole interdigital bandpass filter (425 MHz - 431 MHz). The output of the bandpass filter feeds a PC Electronics model TVCX-70 crystal controlled, GaAsFET downconverter. The downconverter shifts the 426.250 MHz incoming signal to 45.750 MHz (standard USA television receiver IF frequency). A low-noise IF pre-amplifier designed around a Motorola MRF-901 transistor follows the downconverter. The downconverter then feeds a modified Holland Electronics model HDM-1 television demodulator. The modifications include a direct IF signal input, and a noise-activated audio squelch circuit (KD2BD design). The downconverter also serves as the front-end for the control link receiver, permitting a single downconverter, antenna, and duplexer to be used for transmitting, receiving, and remote control operations simultaneously. The control link receiver is homebrew (based on a Motorola MC3362 chip).

The demodulated audio and video signals from the HDM-1 are then fed into a Micro Computer Concepts model VS-100 microprocessor-based ATV repeater controller/remote video switcher. An Elktronics video I.D. board was added to the controller to permit periodic station identification through the VS-100. Other modifications to the VS-100 include the addition of a high-performance video operated relay circuit.

During periods when the US Space Shuttle is in orbit, regular repeater service is suspended so that video coverage of the shuttle mission may be carried through the repeater system. NASA Television programming carried by the repeater is received from the AMC-6 satellite (transponder 17C) using a 10-foot dish antenna, a Skyvision C-band LNB, and a Pansat model 2700A MPEG-2 digital satellite receiver. Audio and video from the satellite receiver are fed into the repeater controller for transmission through the repeater system.

The video output from the controller is processed through an FM Systems Model VM711 Video Master Automatic Gain Control System. The VM711 is a baseband video processor that stabilizes video levels, clamps out low frequency interference, and automatically corrects luminance-to-chrominance inequality through a time-gated control system. Processed video available from the VM711 is often of higher quality than that of ATV signals received by the repeater.

Conditioned video from the VM711 feeds a television transmitter consisting of an exciter (KD2BD design) that features outstanding quality as well as a choice of subcarrier and/or on-carrier audio transmission methods. The 2-watt RF output from the exciter feeds a Pauldon Associates intermediate power amplifier designed around a Mitsubishi M67728 55-watt RF power module. The output of this amplifier is approximately 20-watts PEP, and is used to drive a Teletec 150-watt linear power amplifier to full rated output power. The Teletec amplifier then feeds a vestigial sideband filter consisting of another ICM model FL407 7-pole interdigital bandpass filter (438 - 444 MHz), and the TX/RX Systems duplexer before feeding the hardline and antenna system.

An Astron 13.8 volt, 50 amp regulated DC power supply, a color video monitor, 439.250 MHz on-air receiver, and video switcher round out the major components of the repeater system.

The Brookdale Amateur Television Repeater System is a long-term, on-going educational project. Future plans include replacing the existing antenna system with a much improved design, adding an FM repeater mode (426.250 MHz FM in / 439.250 MHz FM out), adding an additional power amplifier for greater coverage, and replacing the repeater controller with something a bit more reliable.

rack photo

A recent photo of the equipment rack

dish photo

Photo of the satellite dish used for NASA-TV reception

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