Re: Choosing uplink and downlink frequencies for 1 kg sateli
The use of UHF downlinks is very strange indeed. It seems to me it's just a copy and paste design habit of many new cubesat teams. Please also consider that many teams don't have an RF specialist but rely on past designs which may not always be optimal.
Separation between the TX output and RX input is the only reason to do this.
But this is an argument of the past, as many new components are around to provide good filtering.
There are numerous advantages of using UHF (2m) uplinks and VHF downlinks (70cm), the so-called mode UV. The most important ones are:
- The IARU likes the UV mode (UHF up, VHF down), so coordination will be easier. VU mode is the recommended mode by the IARU.
- The VHF amateur band satellite segment has primary status all over the world. UHF 70cm does not.
- The downlink signal on VHF is better received than UHF (so friis formula is right!)
- The downlink signal on VHF has less doppler shift so its easier to tune
- COTS antennas and transceivers are available for mode UV
- The higher path loss on UHF is easily solved using more TX power on the ground side
- Transmitters are more simple to build on VHF (but the difference is not that great..)
An example UV mission is Delfi-C3
http://www.delfic3.nl.
If someone is planning a new cubesat mission, UV would be the preferred mode.
If there are good reasons to use mode VU, this can always be an option. Many cubesats sucessfully carried out their missions using the VU scheme, but once again, the recommendation of the IARU is still UV.
Regards,
Wouter Weggelaar
PA3WEG