LUSAT CW TELEMETRY MODULE
There was an area in the satellite originally planned to hold memory, but due changes to larger scale integrated circuits, (miniature monolithic circuits), all the memory went to the second satellite module, thus freeing an area(named lately 'This Space For Rent'), allowing for other experiments. Here, was where this circumstance was profited to put a CW beacon's, whose design and construction was made in Argentina.
The beacon consists of a transmitter of 600 mW and a miniature intelligent controller, that will give telemetry data, independent of the satellite onboard computer. The computer controller consist in a MC146805 CPU and C-MOS auxiliary IC's to get a low energy consumption.It have eight digital analog input/output gates for take the datas for transmit. The circuit added a Watchdog for reset the controller in a fault case.The telemetry program was loaded in a EPROM for space used, transmit datas in MORSE code.This program was loaded seven times with a different number version. Furthermore a control program was loaded, (worm), for detect any anomaly made by the radiation in the telemetry program loaded in the EPROM and in a fault case change to a new version.
The specification for the CW transmitter for a 437.125 MHz frequency, was that should operate with an efficiency same or best of 65 %. This is calculated dividing the output of the final power by the total power of D.C., (oscillator,multipliers and final amplifier).
For the transmitter, the design taken was based on the exciter of the main transmitter of the microsat's, that has a conventional oscillator with a 54.8 MHz crystal using a 2N4957, multiplying to 109 MHz. It has two multipliers stages for 218 and 437 MHz. The power output in this range is 1mW.
The final amplifier has two stages. The first uses a MRF 571 transistor, this is switched on/off by the signal in Morse code made by the controller, using a 2N2907 switching transistor. A 2N2222 transistor in the base circuit stabilizes its polarization. This stage was modified to obtain 35 mW of RF in place of the original 100 mW, supporting the efficiency.
The output amplifier consists of an MRF 559 working in class C. The power provided by this stage was near 900 mW, the final adjustment was made to support the best efficiency, that is 750 mW with a total efficiency of 55 %. The output filter was designed to obtain the correct impedances matching and decrease of harmonics output, that on laboratory tests was -45 dB. The beacon's antenna connection was made with a special relay, (latch), to avoid extra load. This relay will stays in a given position until a transfer pulse is received.
This relay switches between the HELLAPS, secondary packet transmitter, or the CW Beacon. The beacon’s tests was made in CITEFA, (Argentina Technological Research Center), before send it to USA, to be placed in the satellite. We made vacuum test, thermal test behavior between –30 and +60 deg. C.,and vibration test at 7.3 G.
All OSCARs satellites support very low temperatures at the moment of orbit entry, without telemetry information to know satellite status, thus the module was made to run on the worst expected and unfavorable conditions. A good performance was obtained working from –35 deg. C.
This beacon sends CW telemetry at 12 WPM at 437.125 MHz in reduced Morse codification, allowing energy savings of 44 %.
The beacon has one status channel and eight data channel. The following is the data of each channel and the formula necessary to obtain the correct value.
CH 1 : N1 +5 voltage 636/N1 = Volts
CH 2 : N2 +10 battery voltage .064*n2 = Volts
CH 3 : N3 CW transmitter temp .354*(134.7-N3) = Deg. C.
CH 4 : N4 Output power TX. ((10.9+N)^2)/40.1= mWatts
CH 5 : N5 Box temperature #4. .356*(136-N5) = Deg. C.
CH 6 : N6 +10 v current .7*N6 = Ma.
CH 7 : N7 +Z voltage panel. .15*N7 = Volts.
CH 8 : N8 +8.5 voltage .056*N8 = Volts.
The message format is the following:
LUSAT HI HI VL N1 N2 N3 N4 N5 N6 N7 N8
V = is the letter of eprom’s program version.
The program was repeated seven times, to avoid crash’s for radiation degradation. If the first version is out of service, the second will be loaded and executed.
L= is the ram MC146805 microprocessor result test; if L=O the ram is ok;
if L=E there had been a error detected.
N1 to N8 are telemetry data of each channel.
For the numeric values, it has been adopted a compact codification, thus
allowing for a more effective power usage, this codification is as follows:
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