h1. Preliminary Design

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h3. Introduction

This document covers the preliminary design decisions for the *Ground Sphere* ground station hardware.  The document includes three sections: technical background on *SkyCube's* radio, hardware design of *Ground Sphere*, and software design of *Ground Sphere*.  The design is structured in parallel with the [[Requirements Document]] to ensure all requirements are satisfied.

h3. SkyCube Radio Details

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h3. Hardware Design of Ground Sphere

* TR 1.1 Enable users to receive "space tweets"
** TR 1.1.2 Receive radio signals on 915 MHz
*** Antenna
*** "Preamp":http://www.g0mrf.com/432LNA.htm
*** "RTL2832U SDR":http://www.realtek.com.tw/products/productsView.aspx?Langid=1&PFid=35&Level=4&Conn=3&ProdID=257
* h3. TR 1.2 Be easy to assemble from kit components
** TR 1.2.1 Time to assemble
*** Ground station will be shipped as a kit
** TR 1.2.2 Tools for assembly
*** Preamp will ship already assembled, ground station structure will include all drill holes and all other component fabrications steps 
* TR 1.3 Have low shipping costs for the packaged kit
** <insert max dimensions here?>
* TR 1.4 Operate using a modern Windows PC
** TR 1.4.3 Hardware must connect to PC using standard port(s)
*** The SDR connects to host computer through USB 2.0
* TR 1.5 Hardware must be robust
** All connectors will be designed to ensure long life (internally mounted, have adequate strain relief, etc)
* PR 2.1 Budget
** PR 2.1.1 Unit cost
*** <insert current materials cost here from BoM>

h3. Software Design of Ground Sphere

* TR 1.1 Enable users to receive "space tweets"
** TR 1.1.1 Predict SkyCube flyover opportunities
*** Using "GPredict":http://gpredict.oz9aec.net for flyover prediction
** TR 1.1.2 Receive radio signals on 915 MHz
*** SeeDeR software (provided by Southern Stars) can tune SDR to 915 MHz
** TR 1.1.3 Decode "space tweet" message from SkyCube
*** SeeDeR software (provided by Southern Stars) can decode the BPSK-modulated, unencrypted AX.25 data packets sent at 9600 baud "space tweets" sent out by *SkyCube*
** TR 1.1.4 Account for Doppler shift
*** SeeDeR software (provided by Southern Stars) will be updated to account for Doppler shift
* TR 1.4 Operate using a modern Windows PC
** TR 1.4.1 Software must run on Windows
*** GPredict runs on Windows 7
*** SDR drivers <get link from Aaron> run on Windows 7
*** SeeDeR runs on Windows 7
** TR 1.4.2 Software must be easy to install
*** GPredict includes a Windows installer
*** SDR drivers include a Windows installer
*** Southern Stars will provide a Windows installer for SeeDeR