Below you will find the link budget summary calculated for a few distances during the interplanetary cruise of UNITEC-1. The link budget calculator sheet containing all the details is available here.
| Parameter | Value | ||||
| Frequency | 5840 MHz | ||||
| TX Power | 4.8 W / 6.8 dBW / 36.8 dBm | ||||
| TX Ant Gain | 5 dBi | ||||
| EIRP | 11.8 dBW | ||||
| Distance (km) | 20.000 | 200.000 | 2.000.000 | 15.000.000 | 20.000.000 |
| Distance (AU) | 0.0001337 | 0.0013369 | 0.0133692 | 0.1002687 | 0.1336916 |
| Free Space Loss | 194 dB | 214 dB | 234 dB | 251 dB | 254 dB |
| Atm. losses | 2 dB | ||||
| Signal at RX ant | -184 dBW | -204 dBW | -224 dBW | -242 dBW | -244 dBW |
| Pointing loss | 0.4 dB | ||||
| Receiver G/T | 23 dB/K | ||||
| S/N0 | 67 dBHz | 47 dBHz | 27 dBHz | 10 dBHz | 7 dBHz |
| SNR @ 500 Hz BW | 40 dB | 20 dB | 0 dB | -17 dB | -20 dB |
| SNR @ 100 Hz BW | 47 dB | 27 dB | 7 dB | -10 dB | -13 dB |
Assumptions
- Attenuation due to rain, ionosphere and atmospheric gasses set to 2 dB[2]
- TX power is 4.8 watts/antenna[3].
- TX antenna is microstrip patch, linear, assuming 5 dBi gain[3].
- Our beam width is 0.5° and I assumed a pointing error no greater than 0.1° (very optimistic) giving a 0.4 dB pointing loss.
TBDs and TBCs
- Measure the receiver noise floor, i.e. local interference contribution to sky temperature (important)
- Re-assess sky noise taking expected solar noise, etc. into account[2]
Conclusions
- An optimistic estimate suggests that we should be able to receive UNITEC-1 up to 10-15 million km distance.
- There is plenty of margin in the beginning and we can use a low gain antenna for initial acquisition. The IKEA dish has ~25 dBi gain and it could be used up to 1 million km where after the trajectory is hopefully well known.