Ground Sphere Operating Manual v0.2


Instructions on connecting the antenna, software defined radio dongle, and computer together to operate the ground station go here. Note, be sure to talk about if the antenna should be mounted outside and if so, how.


There are two pieces of required hardware. The antenna/receiver unit and a user provided laptop

User provided laptop, minimum system requirements

  • Windows 7 operating system
  • 1GHz single core CPU
  • 1GB RAM
  • Open USB port

To install the antenna/receiver


There are two pieces of software needed to operate the ground station. The satellite tracking software, GPredict, and the AX.25 decoder, SeeDeR.

GPredict Operating Instructions

The user manual for gpredict is available at Chapter 2 covers the basic operating instructions.

SeeDeR Operating Instructions

  • Ensure you have an RTL-SDR device drivers and the SeeDeR installed correctly via the Software Installation instructions.
  • Launch SeeDer by running the SeeDeR.exe from the folder where you installed SeeDeR
  • If the RTL-SDR device is detected, you should see a moving waterfall display
  • You may wish to tune to an FM station to check basic performance:
    • Type a typical FM frequency (say, 100,100,000) into the "Center" box.
    • Click in the waterfall display to hit the exact center of a station (or type the frequency into the "Frequency" box).
    • Select "WFM" under "Demodulation", and you should hear FM audio, and possibly see RDS data.
  • To pick up AX.25 data:
    • Select "AX.25" under "Demodulation"
    • Select the proper baud rate and modulation under "AX.25 Settings"
    • Settings for SkyCube:
      • Uplink: 450 MHz, 9600 baud, 2FSK modulation
      • Downlink: 915 MHz, 57600 baud, BPSK modulation
      • Tweets: 915 MHz, 9600 baud, BPSK modulation
Extra notes:
  • The sample rate under "Device Settings" can be left at the default 2.048 MS/s. Higher settings do not increase performance, and have worse frequency response.
  • If you have a high performance computer, select "Very High" for visualization quality.
  • You may have to play with the ACG and gain settings for proper reception, especially for local transmissions (at high power levels, the input data gets clipped unless the gain is lowered).
  • Try clicking the edges of the waterfall window, as well as clicking and dragging.
  • Bookmarks allow you to save most of the settings and quickly swap to them
  • SeeDeR should work fine with more than one RTL-SDR device. Settings are associated with a device, so you can see uplink and downlink data simultaneously.

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