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

VLBA L GHz synthesizer – 3 per antenna – Maintainability / Spare parts are becoming a concern – Coarse tuning steps The new RDBEs eliminated the fine tuning of the Baseband Converters The two L104s 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 2

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 3

Synthesizers Advances in technology that may help: – Field Programmable Gate Arrays (FPGAs) 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 4

Questions? Project Engineer Jim Jackson (575)