Radio Astronomy Box (RABox)

Starting point

While searching for a cutting-edge design for a next radio astronomy receiving system which is still feasible for amateur radio astronomers I came to the following basic idea:

Picture 1: Basic idea of a powerful and flexible radio astronomy receiving system

Connecting a data stream to a PC

The basic idea is to use a standard network cable for Gigabit Ethernet which is specified for transferring upto 100 MBytes/sec. over a distance of upto 100 m. Spare wires in the Gigabit Ethernet cable could possibly be used for supplying power to the receiving device.

The proposed connection would allow for doing signal sampling in the receiving device of upto 100 MSamples/sec. @ 8-bit respectively upto 50 MSamples/sec. @ 16-bit. I have got some experience in a professional project and saw that the mentioned data volume can be transferred reliably to a fast PC of about 3 GHz clock rate. Less capable computers with 100 MBit Ethernet network cards could still operate the device at a lower rate of upto 10 MSamples/sec.

A GigE Vision 1.0 standard has been released in May 2006 which describes all technical details for operating digital cameras at high speeds over Gigabit Ethernet cable. When following that standard also for a RABox that new device could even be operated by standard software that usually obtains a data stream from a digital camera and which would alternatively be used to obtain a comparable data stream from a radio astronomy receiving device. Possibly standard software would just write all data on a hard disk for later processing. A special software would be needed for doing real radio astronomy processing. However, a "first view (noise image)" would be possible by GigE Vision standard imaging software.

Receiving parameters

There are no real limits that are intended to be put on the receiving parameters by the following considerations. Instead, the proposed parameters could be seen as a "minimal MAXIMUM approach" for doing useful radio astronomy.

The input range should cover the hydrogen line along with the first harmonic of the hydrogen line as well as the complete intermediate frequency range of a SAT LNB. Further all lower frequencies are also of high interest. those considerations provide to a desired input frequency range from 0 to 3 GHz.
A 5 mV signal on the input should provide to a full scale response on the digital output
When connecting multiple of those receivers in an interferometer network a phase synchronisation by an external clock, e.g. a 10 MHz signal from a GPS receiver is needed.
The intermediate frequency bandwidth should allow for doing observations with various bandwidth settings upto the maximum bandwidth of 100 MHz @ 8-bit resolution respectively 50 MHz @ 16-bit resolution.

All hints and feedback is welcome in the ERAC mailing list discussion@eracnet.org

Eckhard Kantz

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