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AO-7 history and info

enjoy guys,



        Two to ten meter translator.
           Input 145.850 to 145.950 mHz
           Output 29.40 to 29.50 mHz

        70 cm to two meter translator.
           Input 432-125 to 432-175 offs
           Output 145.975 to 145.925 mHz
           Output passband is INVERTED.
           Beacon output at 145.975 mHz

    Additional beacons at 435.1 mHz and 2304.1 mHz (The FCC has notified AMSAT
    that the 2304 mHz beacon should be "prevented from transmitting" until
    further notice.)

    Operating Modes:

        Mode A. 2 to 10 motor translator ON. 29.502 mHz beacon 02
        (transmitting 20 wpm Mores code telemetry or codestore info). 435.1
        mHz beacon operable (normally ON. transmitting 850 Hz FSK teletype

        Mode B. 70 cm to 2 meter translator ON (high power nods). 145.975
        mHz beacon ON (modulated as per 29*502 beacon).

        Mode C. 70 cm to 2 meter translator ON (quarter power mode). 145.975
        mHz beacon ON per mode B.
        Mode D. Recharge mode. Both translators OFF. 435 mHz beacon operable
        (Commanded on for telemetry readout)

    Operating Schedule: (Planned after initial spacecraft checkout)

        Mode A. Sunday, Tuesday and Friday
        Mode B. Monday, Thursday and Saturday
        Mode D or special experiments on Wednesday

    Planned Orbit:

        Similar to that of OSCAR 6; 1460 km altitude circular orbit, 102
        degree inclination (retrograde, sun-synchronous orbit), period or
        115 minutes, about 1/2 orbit (1 hour) out of phase with the OSCAR 6

    For additional info, see Feb 1974 QST. The following information Is from
    AMSAT NEWSLETTER for Sept 1974:


    AMSAT-OSCAR 7 contains two basic experimental repeater packages, redundant
    command systems, two experimental telemetry systems, and a store-and-forward
    message storage unit. The spacecraft in solar powered, weighs 65 pounds, and
    has a three-year anticipated lifetime. It contains beacons on 29.50, 145.98,
    435.10 and 2304.1 MHz.

    Communications Repeaters

    Two types of communications repeaters are aboard the spacecraft, only one of
    which operates at a time. The first repeater is a higher power, two-watt
    version of the one-watt two-to-ten motor linear repeater that flow on the
    OSCAR 6 mission. This nit receives uplink signals between 145.85 and 145.95
    MHz, and retransmits them between 29.4 mid 29.5 MHz an the downlink. A 200
    milliwatt telemetry beacon provides telemetry data on 29.502 MHz.*
    Approximately -100 dBm is required at the repeater input terminals for an
    output of 1 watt. This corresponds to an eirp from the ground of 90 watts
    for a distance to the satellite of 2,000 miles and a polarization mismatch
    of 3 dB.

    The second repeater, constructed by AMSAT Deutschland e.V., AMSAT's
    affiliate in Marbach, West Germany, is a 40-kHz* bandwidth linear repeater.
    It employs an 8-watt PEP power amplifier using the envelope elimination and
    restoration technique to maintain linear operation over a wide dynamic range
    with high efficiency. This repeater has an uplink from 432.125 to 432.175
    MHz, and a downlink from 145.925 to 145.975 MHz. Since the uplink band in
    shared with the radiolocation service, an experimental pulse suppression
    circuit is incorporated in the repeater to reduce the effects of wideband
    pulsed radar interference in the uplink. Developmental versions of this
    repeater have flown in high-altitude balloon experiments in Germany, and
    aircraft flight tests of the repeater prototype unit. A 200 milliwatt
    telemetry beacon on 145.975' provides telemetry data. Approximately So
    W.*eirp is required to produce 3 watts of repeater output at a range of
    2,000 miles assuming.& polarization mismatch of 3 db.

    The two repeaters are operated alternately by means of a timer arrangement,
    but repeater selection and output power control can also be accomplished by
    ground command. Each of the repeaters includes a keyed telemetry beacon at
    the upper edge of the downlink passband to provide housekeeping data and to
    provide a frequency and amplitude reference marker to assist the amateur in
    antenna pointing, Doppler frequency compensation, and setting uplink power
    level. The cross-band 146-to-29.5 and 432-to-146 KNO design of the two
    repeaters will permit the amateur to monitor his own downlink signal easily,
    and consequently, he can adjust his power and frequency to continually
    compensate for changing path loss, repeater loading and Doppler shift.

    Command System

    Redundant command decoders of a design similar to the unit proven highly
    successful in OSCAR 6 will be flown. The decoder has provisions for 35
    separate functions, and is designed to provide a reliable means of
    controlling the emissions of the repeaters, beacons and other experiments
    aboard the spacecraft.

    Telemetry and Message Storage Systems

    AMSAT-OSCAR 7 contains two experimental telemetry systems designed for use
    with simple ground terminal equipment. The first system, developed by the
    WIA-Project Australis group in Australia, telemeters 60 parameters in 850-Hz
    shift, 60 WPM five-level Baudot teletype code to permit printout on standard
    teletype equipment in a format readily convertible for direct processing by
    small digital computer. The second system telemeters 24 parameters as
    numbers in standard Morse code and can be received with pencil and paper.
    This system was used on OSCAR 6 and proved highly successful as a reliable
    means of obtaining real-time telemetry data.

    An experimental Morse code message storage unit, Codestore, capable of
    storing and repeatedly retransmitting 18-word More& code messages loaded by
    ground stations in also aboard AMSAT-OSCAR 7. This unit was first flown on
    OSCAR 6.

    The teletype telemetry encoder amplitude-modulates telemetry beacons on
    29.50 MHz (200 mw), 145.98 MHz (200 mw) and frequency-shift keys the beacon
    on 435.10 MHz (300-400 mw), as selected by ground command. The Morse code
    telemetry encoder and Codestore message storage unit directly key these
    beacons as selected by ground command.


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