Archive:Noctar

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Organizational

Contact Simon if you want to use the system. You should have knowledge of radio frequency technology and regulations. There will be a test.

Technical

• Direct Quadrature Receiver/Transmitter
• Separate LOs for receive and transmit paths
• 55 MHz IF lowpass filter
• 2x125 MSa/s 12 bit ADCs
• Altera EP4CGX22C FPGA with DSP core
• 2x250 MSa/s 16 bit DACs

Projects

Rewriting the FPGA firmware

The factory firmware has several drawbacks that make it difficult to use the system easily:

• Decimation is done in 5 stages, each halving the sample rate. This leads to an awful lot of digital filter noise, and decimation 32 is not really sufficient for most applications.

 * New design using a 2x16 multiplier FIR filter with symmetry handling and accumulator (i.e. 31 coefficients in a symmetric lowpass filter design without decimation)
 * Additional fixed IIR filters implementing high decimation factors

• Table based NCO. This takes up lots of FPGA space, and has limited accuracy.