Synthesizers

1. Synthesizers Presentation – 1 Nov 2011 • Jim Jackson, NRAO • EVLA/VLBA Project / Systems Engineer

2. Synthesizers • VLBA L104 2-16 GHz synthesizer • 3 per antenna • Maintainability / Spare parts are becoming a concern • Coarse tuning steps • The new RDBE’s eliminated the fine tuning of the Baseband Converters • The two L104’s driving the IF converters should be finer resolution • Earlier proposal was not funded • EVLA and ALMA evaluating synthesizers for upgrade paths • Current designs already approaching 10 years old • Performance / reliability is good but not ideal • No currently funded efforts • EVLA / VLBA funding unlikely in near future

3. Synthesizers • Synthesizer designs being investigated • FPGA Direct Digital Synthesis (DDS) with direct multiplication to Microwave frequencies • Switched fixed frequency filters • Tuned filters (such as YTF) • Matt Luce / Kerry Shores / Jim Jackson investigating • FPGA DDS providing multiplied reference for PLL / Oscillator based Synthesizer • A different variant than current EVLA / ALMA designs • Chip Scott / Rob Long investigating • Sigma-Delta DDS based synthesizer • Proprietary work by an outside vendor • Could utilize either of the above solutions

4. Synthesizers • Advances in technology that may help: • Field Programmable Gate Arrays (FPGA’s) with: • faster clock speeds • Higher speed SERDES interfaces • Digital to Analog converters • Much faster clocks and higher resolution reduce Spurious Free Dynamic Range • Sigma Delta D/A converters • Low phase noise alternatives to YIG oscillators

5. Questions? Project Engineer Jim Jackson jjackson@nrao.edu (575) 835-7132