1024 MHz vs 512 MHz Bands for VLBI

1024 -MHz vs 512 -MHz Bands for VLBI 2010? East Coast VLBI Meeting Feb. 23 -24, 2011, Haystack Observatory Bill Petrachenko

Method for comparing 1024 and 512 MHz BW Systems n Compare performance of a variety of 1024 - and 512 -MHz sequences. n Figure of merit for comparison is minimum SNR/band for 5 -σ broadband delay detection (lower is better) – see next slide. n Sequence variations n 4 use 512 -MHz bands. n 5 use 1024 -MHz continuous bands. n 2 use 1024 -MHz bands with possible spaces. n Some ensure full overlap with both S and X-band (green shading), which is beneficial for S/X compatibility modes. n Some avoid the Direct Broadbast Satellite (DBS) bands (purple shading) to avoid possible RFI problems. n Some use high frequencies to access lower source structure. n Some assume 50% power at high frequency (darkened bands) to emulate feed/LNA roll-off.

VLBI 2010 Frequency Sequences SNR/band for 5 -σ detection (Min flux (10 -s, 16 -Gbps)) Relative data volume X-band DBS S-band DBS 9. 0 (221) – 2. 33 11. 6 (286) – 3. 87 512 -MHz bands 11. 5 (284) – 3. 80 11. 8 (290) – 4. 00 6. 4 (157) – 1. 18 6. 8 (168) – 1. 33 1024 -MHz bands 7. 3 (179) – 1. 53 7. 4 (183) – 1. 57 7. 6 (190) – 1. 56 5. 9 (145) – 1. 00 Split bands 7. 2 (179) – 1. 49 2 4 6 8 GHz 10 12 14

Compatibility Concern: RDBE (2 x 512 -MHz) vs DBBC 2010 (1 x 1024 -MHz) n Six possible modes were considered n 4 of 6 are compatible (See following slides) n Some cases assume digital sideband flipping n Easy to implement (flipping the sign of alternate samples).

Sampling/BW Compatibility 2048 -Gsps vs. 2 x 1024 -Gsps Nyquist filters 512 512 2560 1024 -Gsps 2560 2048 -Gsps Samplers 2560 512 2560

Sampling/BW Compatibility 2048 -Gsps vs. 2 x 1024 -Gsps Nyquist filters 512 2560 Sum 512 2560 512 1024 -Gsps 512 2560 2048 -Gsps Samplers 2560 512 2560

Extra slides

BW f 1 f 2 f 3 f 4 snr 1 snr 2 Smin 0. 5 2. 2 4. 2 5. 7 9. 2 9. 0 7. 9 221 8. 4 2. 2 0. 5 2. 2 4. 2 8. 0 8. 5 11. 6 10. 3 286 8. 3 1. 5 0. 5 2. 2 5. 2 6. 7 12. 7 11. 5 5. 3 284 3. 6 2. 2 0. 5 2. 2 5. 2 6. 7 12. 7 11. 8 6. 8 290 5. 4 2. 7 1. 0 2. 2 4. 2 6. 7 11. 7 6. 2 6. 4 157 7. 9 2. 0 1. 0 2. 2 5. 7 7. 7 12. 7 6. 8 5. 9 168 6. 5 1. 9 1. 0 2. 2 6. 2 8. 2 12. 7 7. 3 6. 2 179 6. 4 1. 8 1. 0 2. 2 4. 7 7. 2 12. 7 7. 4 7. 2 183 8. 5 2. 4 1. 0 2. 2 5. 7 7. 9 12. 7 7. 6 7. 7 190 8. 8 2. 1 1. 0 2. 2 3. 2 4. 7 5. 7 8. 2 8. 7 12. 7 13. 7 5. 9 145 7. 3 1. 9 1. 0 2. 2 3. 2 4. 7 5. 7 8. 2 8. 7 12. 7 13. 7 7. 2 179 8. 4 2. 2 Δτ Δτ