Ground Sphere CubeSat Ground Station

Big picture¶

1. Weeks 1-3
   1. J - setup wiki, versions, initial questions, requirements, and initial set of milestones
   2. Aaron - build Prototype 1
      1. Calculations for amplifier and antenna due Oct 10
      2. Fabrication of Antenna Components (body, aerial loops, ground plane - Jaye, phasing loop) due Oct 18 (accounts for Aaron's travel)
      3. Fabrication of preamp for 900MHz due Oct 23
      4. Protoype Assembly due Oct 25
   3. Tim - get list of targets in same frequency range of SkyCube due by Oct 25
   4. Scott - Distribute AX.25 software to team due by Oct 18
2. Week 4
   1. Aaron - testing (lots and lots of testing) due Nov 1 [note, there will be a go/no go point after testing for the remainder of the schedule based on how testing goes]
3. Week 5
   1. Full team - prototype 1 debrief and lessons learned in prep for kit version design due by Nov 8
4. Weeks 6-7
   1. Full team - design discussions to work out issues for first kit prototype due by Nov 22
5. Weeks 8-11(?)
   1. Aaron - Build prototype 2 (first kit prototype) due Dec 13
   2. Full team - debrief prototype 2 due by Dec 17
6. Weeks 12-15(?)
   1. Aaron - Build prototype 3 (second and final kit prototype) due by Jan 4
   2. full team - debrief prototype 3 due by Jan 7

OK, I have entered the schedule from the post above into the issue tracking system. It now displays in both the Roadmap and the Gantt tabs. Please be sure to update issues as you complete the work on them. I am sure we will have to add more issues as we find bugs or refine the schedule.

Looking forward to the Prototype 1 build and tests.

I have two pieces of news... first the bad, then the outstanding.

Prior to modifying the preamp circuit, I performed some baseline tests on it in the UHF (435MHz) range. The noise figure I got was around 5dB, nowhere near the advertized 1dB. Further the gain I got was closer to 12dB, not 20 as advertized. Online research shows that this design's quality control was all over the map. In order to do the calculation for the component change, I first checked the center of the frequency band of the existing filter and found it to be at 167MHz, not in the UHF band at all. All this leads me to believe that this is a poor design and too much time would have to be spent making sure the kit units worked as advertised.

In looking for a replacement I found this preamp kit: http://www.g0mrf.com/432LNA.htm It has 20dB of gain with a noise figure of 0.6 at 915MHz, and is able to amplify signals from 145MHz to 1.5GHz. Further, it is able to run on 5VDC simply by bypassing the voltage regulator. This makes it ideal for our uses, and allows the ground station as designed to tune into standard UHF satellites as well by swapping out the aerials and phasing loop.

In the grand tradition of ham radio (who were sharing designs a century before open hardware), this design is free for use, or we can buy a kit, or we can buy the board. I have contacted the designer in order to purchase a kit for $35.00 (including shipping from the UK). Should this work as well as I expect, the bare board is available for $10.00, and I may be able to source the parts in the US for cheaper. The other benefit to this design is that it is a single sided PC board with a ground plane on the back, making construction easy (as SMD circuits go) and giving us a shielded place to locate the SDR to further reduce the noise floor.

Project wise, this brings the preamp into a known quantity, and not in need of a redesign. To that end, I am going to post the antenna component spreadsheet and show the math tasks for this week as complete.

Thanks for the heads up, Aaron. I'm not an EE or a radio guy, but the new pre-amp sounds promising. I love reusing existing hardware (and designs). Do you have an estimated delivery date for the kit? I am asking to compare it to the current project schedule.

Sorry... missed the post above. I received the preamp kit about 7 days after ordering. Quite impressed since it went from England to the backwoods lab here in a week.