RaDAR – Automating field SatComms


I’ve always promoted SatComms for use in RaDAR. It certainly has its place there.

Recently there has been renewed interest in the satellites in South Africa and we are starting to use the relatively new cubesats and the CAMSATS. The CAMSATS prompted this article as I have some new questions that need answers. The CAMSATS are amazing satellites and they fly in “Formation” requiring a lot of attention from the satellite user switching in the appropriate frequencies as each flies from horizon to horizon in quick succession!

Working “half duplex” is fine when there are two people on the satellite at one time but when there are three or more it becomes quite challenging with great risk of interfering with possible other QSO’s taking place within the pass band of the transponders.

It’s still good practice to do things by hand and should be practiced but once mastered it’s more convenient to utilize a little computer assistance. I used to use SatPC32 which worked well with the 847 I used to have. CAT control of dual VFO rigs for satellites works but it has its problems! While the VFO’s are updated and you press the PTT at the wrong time it’s possible that you may transmit using the wrong VFO, especially with the 817. The 897 seems to be a little more “tolerant”. If you are monitoring the downlink on another radio it’s possible then that you transmit on the downlink frequency blasting your headphoned ears with strong audio! This is the problem I have and I need to devise a means of working RaDAR SatComms in the best possible way. It also needs to be done to protect the receiver radio!

The proposal.

Just this weekend I rebuilt my HP 210 NetBook computer to control the FT-897d via CAT only to initially set up the uplink and downlink frequencies on the dual VFO’s (Working SPLit). The receive VFO frequency will then indicate what frequency the FT-817nd should be set for the downlink. From there on it’s manual tuning of the higher frequency being it the uplink (u/v) or downlink (v/u) working full duplex and able to listen to your own signal through the transponder and of course others. The process of “Netting” is used to get onto another stations frequency.

Note, each radio has a direct coax connection to the 2m or 70cm yagi of the Arrow antenna. I use the more flexible (but lossy) RG58cu coax but it works acceptably well.

There is still quite a measure of manual control but better than working “blind” and of course keeps the RaDAR operator sharp and focused without the need to look up written or printed frequencies on paper (usually in the dark). Of course this relies on the computer.

I have found too, that tracking the satellite by hand is easier while standing so the rigs should be arranged such that they are easily accessible even while standing.

I use the 817’s shoulder strap and hang it over my Arrow’s tripod but still need to find a way to do something similar with the FT-897d. I power both radios off a 7 A/Hr SLAB that usually sits on the ground.