We get more reliable data downloads from the satellite using the VHF downlink, so swap to this after having established initial communications with the VHF uplink and UHF downlink. We typically receive 30 to 60 seconds data from Sunsat on the UHF downlink, and then reverse the band choice.
The reason why the VHF downlink gives stronger signals is because an antenna such as a dipole that is designed for 145.825 MHz has nearly three times the dimensions of one designed for our UHF frequency. It consequently has an 'effective area' that is nine times larger than at UHF, so receives nine times more power for similar strength transmissions. Actually SUNSAT's VHF transmitter power output is only about half that of the UHF transmitter, so the received signal strength is about four times better on VHF than UHF.
The VHFdownlink can often be heard on a hand-held with a 15cm 'rubber duckie' antenna. When we are running at 9600 bd, the modulation sounds like noise, which is not the most exciting to listen to!
During this week, three of the best daytime passes (Tuesday 4 May-Thursday 6 May) are being devoted to supporting the SARL's (South African Amateur Radio League) 'School's Radio Roundup'
SUNSAT will be transmitting a speech message in the passes starting at 14:20 SA time on 5 May and at 13:35 on 6 May. See http://www.sarl.org.za for details.
The printout below gives AOS (Acquisition of signal) times for Cape Town. Pretoria times will be about 2 minutes later. On daytime passes not supporting the SARL, you should be able to hear the downlink with packed telemetry data being downloaded. In some months time we will make telemetry decoding software available, but our software team's time is needed elsewhere at the moment.
SCHEDULE FOR SUNSAT (SO-35) PASSES FOR Cape Town (corrected!)
NOTE: Times are ZULU (i.e. GMT) and are from the USA orbital elements for SUNSAT. However, these are in fact Orsted's elements, and SUNSAT passes 6 minutes after Orsted. So add 2 hours and 6 minutes to get SA time!
DATE AOS MAX LOS EPOCH Elev deg AZ deg ORBIT No 04MAY99 222450 223132 223814 04MAY99 18 EL 112 1014 05MAY99 000205 001001 001756 05MAY99 55 EL 278 1015 05MAY99 014619 014956 015332 05MAY99 3 EL 264 1016 05MAY99 103724 104151 104618 05MAY99 6 EL 96 1021 05MAY99 121420 122123 122827 05MAY99 78 EL 171 1022 05MAY99 135457 135942 140426 05MAY99 7 EL 241 1023 05MAY99 214737 215231 215725 05MAY99 6 EL 118 1028 05MAY99 232227 233023 233818 05MAY99 64 EL 101 1029 06MAY99 010319 010948 011617 06MAY99 14 EL 269 1030 06MAY99 113503 114145 114828 06MAY99 33 EL 91 1036 06MAY99 131419 132033 132646 06MAY99 20 EL 246 1037 06MAY99 224344 225105 225826 06MAY99 28 EL 110 1043 07MAY99 002209 002947 003725 07MAY99 34 EL 276 1044 07MAY99 105612 110147 110721 07MAY99 12 EL 93 1050 07MAY99 123416 124106 124757 07MAY99 51 EL 245 1051 07MAY99 141608 141907 142205 07MAY99 2 EL 239 1052 07MAY99 220550 221153 221756 07MAY99 12 EL 115 1057 07MAY99 234204 235004 235803 07MAY99 80 EL 288 1058 08MAY99 012425 012945 013505 08MAY99 7 EL 266 1059 08MAY99 101916 102140 102404 08MAY99 1 EL 97 1064 08MAY99 115436 120131 120825 08MAY99 57 EL 93 1065 08MAY99 133431 133958 134524 08MAY99 12 EL 244 1066