Downlink Specification

1.UNITEC-1 On-board Transmitter

Table. Specification of UNITEC-1 on-board transmitter

Downlink Frequency 5840.000MHz, band width 20MHz
Transmission Power 4.8W/antenna, 9.6W total
Antenna Microstrip patch antenna (x 2)
Modulation AFSK/FM 1200bps, CW 1bps
Type 10M0F2D

2.Data Format

Modulation of 96% of the downlink data is CW with 1bps. Transceiver switching ON/OFF makes signals 1/0. A statement (switching on or off) keeps 1 second.
Only 4% of the total data is 1200 bps AFSK/FM. Basic concept of UNITEC-1 data modulation design is using the 1bps CW to increase a reception power ratio.

2.1 Downlink Cycle

A task sequence for UNITEC-1 OBC is defined as a “major cycle”. It keeps 6 hours. Major cycle sequence is written in a Table 3. Data is transmitted in periods which is shown as 【Downlink】. UOBC (University On-Board Computer) is tested in a statement of “UOBC experiment”. Main OBC (MOBC) communicates with each UOBC and tests them. A result is sent as a experiment data to ground stations.

Table. Major Cycle (6 hours) Content

Time [sec.] Operation Duration [sec.] Operation Number
0  (Waiting) 600  1
600 (0:10:00) [Downlink]Orbital determination downlink(*) 120  2
720 (0:12:00)  (Waiting) 3480  3
4200 (1:10:00) [Downlink]Orbital determination downlink 120  4
4320 (1:12:00)  (Waiting) 3480  5
7800 (2:10:00) [Downlink]Major downlink(**) 2461  6
10261 (2:51:01)  (Waiting) 1176  7
11437 (3:10:37) [Downlink]Orbital determination downlink 120  8
11557 (3:12:37)  (Waiting) 3480  9
15037 (4:10:37) [Downlink]Orbital determination downlink 120  10
15157 (4:12:37)  (Waiting) 3480  11
18637 (5:10:37) [Downlink]Minor downlink(***) 2056  12
20693 (5:44:53)  (Waiting) 1056  13
21749 (6:02:29) End  

(*)Orbital determination downlink

“1”s are sent 120 times, which keeps. It means constant signal is transmitted during 120 seconds. This can be used to acquire parameters such as satellite position and Doppler frequency to determine the UNITEC-1 orbit.

(**)Major downlink

Major downlink includes a housekeeping data and science data. Each UOBC has individual data packet window which modulation is AFSK/FM.

(***)Minor downlink

Minor downlink includes a housekeeping data and science data. UOBC results aren’t included and AFSK/FM communication isn’t operated. Table 4 shows a sequence of the minor downlink.

2.2 Major & Minor Downlink Data Format

Please read this document for the details.

2.3 UOBC Downlink Data Format

Please read this document for the details.

Operator UNITEC1,
May 17, 2010, 6:28 AM
Operator UNITEC1,
May 12, 2010, 1:34 AM