COMS Components Definition

This page defines all the components required for a working COMS system and their functionality (MODEM, TX, Antenna etc.)


HARDWARE


This may be made available by Simon G8PAN, a radio amateur and a professional rf designer. Andy Thomas mentioned our project in confidence to him and he can get us a free "beacon" for 435 MHz. We need to look at the catalogue and enter discussions seriously! M.K.Consultants make very small transmitters etc, unfortunately their full catalogue is not available from there website. The COMS team is looking into this ASAP as the system requirements are vital.

Unfortunately the originally proposed 2.4 GHz (MHX-2400) Development Platform was found not to be suitable as the Doppler shift is too high and the frequency band is not legal in this country. We seriously need to check import/export restrictions, licenses when considering such projects. For any hardware, vibration & vacuum testing is required. The Alinco DJ-C5 was used at Texas Uni. Sedsat used DJ-C1. Looking at the Alinco site though I think there are more updated versions that still may suit our needs.

Some useful links:
Texas uni Cubesat Comms http://www.ae.utexas.edu/courses/ase463q/design_pages/spring03/cubesat/web/Paper%20Sections/4.0%20Communication%20Subsystem.pdf

The alinco homepage http://www.alinco.com/usa.html

Something I read the other day about this company is they do have a site in Portsmouth here in the UK we could order from, so save shipping from abroad. We will need to check export licenses etc with them and check for spaceworthiness.

Their UK site is: http://www.alinco.co.uk/

Manual for DJ-C5 http://www.dis.org/radio/radios/dj-c5/dj-c5ins.pdf.

Generally, in terms of hardware COMS require:
A modem - frequency is modulated to 8-bit binary numbers from the microcontroller into something like morse code. Morse code is encoded into AX.25 protocol by terminal node controller (TNC). TNC ‘packetizes’ data and ‘keys’ the transmitter (adds satellite ‘call sign’ to data)

A transceiver - to transmit and receive data. The transmitter sends signal to ground station via an antenna. Radio operating at UHF at ground station receives data signal and encodes stream to form required for data analysis.

A Ground Station (provided by NSC): Ground Station transmits commands to the satellite (e.g. on/off commands for instruments). Commands received by receiver and processed by microcontroller.

Need to consult catalogue for M.K.Consultants to get further information about certain specifications.


COSTING


Need to consult catalogue for M.K.Consultants


CALIBRATION


Need to consider.


REQUIREMENTS


TRANSCEIVER

Uplink
o Frequency: Approx. 144 MHz
o Form: ?
o Transceiver: ?
o Power Consumption: <500 mW

Downlink 1 (Primary)
o Frequency: 435MHz
o Form: Packet (AX.25 Protocol)
o Transceiver: Alinco?
o Power Output: ?
o Power Consumption: <500 mW

Downlink 2 (Backup)
o Frequency: 435MHz
o Form: ?
o Transceiver: Alinco
o Power Output: ?
o Power Consumption: <500 mW

ANTENNA

Uplink
o Frequency: 144 MHz Band
o Antenna length: ?
o Antenna width: ?

Downlink 1 (Primary)
o Frequency: 435MHz
o Antenna length: ?
o Antenna width:?

Downlink 2 (Backup)
o Frequency: 435MHz Band?
o Antenna length: ?
o Antenna width: ?

TNC (Terminal Node Controller)
o Protocol: AX.25 (for housekeeping data)
o Modulation: Bell202
o Baud Rate: 1200
o Power ?

Downlink by use of AFSK

Need to consult catalogue for M.K.Consultants to get further information about certain specifications.

Camera, pictures -> Hi resolution pics -> 9K6? 38K5? Need to consult PAY.

Data – require compression algorithms! Data needs to be sent within at least 10 minute pass of ground station.


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