Browse Prior Art Database

Simulation of Dual Satellite Telemetry

IP.com Disclosure Number: IPCOM000081680D
Original Publication Date: 1974-Jul-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 5 page(s) / 119K

Publishing Venue

IBM

Related People

Brewer, JR: AUTHOR [+5]

Abstract

A circuit arrangement is shown for synchronizing two sets of data recorded from satellites. The data is originally collected on wide-band analog tape recorders. After recording and playback, data for two separate satellites would be skewed by as much as 2 seconds at the end of a 15-minute run, if an attempt was made to record data from one tape drive on another.

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Simulation of Dual Satellite Telemetry

A circuit arrangement is shown for synchronizing two sets of data recorded from satellites. The data is originally collected on wide-band analog tape recorders. After recording and playback, data for two separate satellites would be skewed by as much as 2 seconds at the end of a 15-minute run, if an attempt was made to record data from one tape drive on another.

The described circuit controls gating to eliminate the clocking jitter between the tapes. Further, data for the second pass is synchronized with the first data tape, by using the data clock from the first pass to clock out the data for the second pass. This is accomplished by a variable-clock oscillator (VCO) operated at 16 times the clock input frequency to generate 16-timing pulses. The clock output is thus synchronized to the timing pulse closest the data output of the first pass.

Fig. 1 shows the equipment configuration for recording the first pass. The GMT generator 10 is set for some time prior to the desired start of data. This is for two reasons: (1) human operators have to start the tape drive, and (2) the GMT circuitry employs an automatic gain setting feature, which requires several seconds to adjust from a no-signal to a normal-signal condition. Also, in this design, GMT 10 will gate on the data clock for the second pass so it must be preset to some time prior to the desired start time.

The recording is accomplished thusly: * The drive 11 is loaded with a degaussed tape. * The GMT comparator 12 is set for the desired data start time. * The GMT generator 10 is set to a time 20 to 30 seconds prior to the comparator time, but is not started. (At this

time, the enable signal from the GMT comparator 12 to the

timing unit in the signal simulator unit (SSU) 13 is down.) * The Simulation Program is started in the CPU 14. This program attempts to write without timeout through

the channel 15 to the SSU 13.

The SSU will accept 1024 bytes of data from the

computer 14 before attempting to clock out data on the

L1 and L2 lines. At this point, it cannot output because

the timing unit 16 is disabled. The SSU 13 will cease to

request data from the channel and the I/O operation is

effectively suspended. * The tape unit 11 is manually started. * The GMT generator 10 is started. This unit begins to step at one second intervals. * The GMT generator steps to the value preset in the GMT comparator 12. * A compare occurs. * The SSU timing unit 16 is enabled and the SSU 13 begins clocking out L1 and L2 data. * Recording proceeds normally to the end of the 15-minute reel.

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At this point, CMT data and Ll and L2 data representing one satellite have been recorded. The tape is rewound and the equipment is configured as shown in Fig. 2. For the second pass, the CMT is derived from the tape 11 and is the GMT recorded during the first pass. The GMT comparator 12 is preset to the same start time as in the first pass and, upon comparing with th...