COVER INFORMATION Station: MEDICINA (Code Mc ) Experiment: Snapshot Ionospheric Testing Observations Exp. Code: N05L2 Schedule Version: 1.20 Processed by SCHED version: 6.01 Release: Late March 2005 PI: James M Anderson Address: Joint Institute for VLBI in Europe Oude Hoogeveensedijk 4 7991 PD Dwingeloo The Netherlands Phone: +31 (0)521 596 542 EMAIL: anderson@jive.nl Fax: +31 (0)521 596 539 Phone during observation: +31 (0)521 596 500 Observing mode: Snapshot observations of sources at 18cm (256 Mb/s) Notes: ALBUS Ionospheric modeling test observations Fringe Finder is 3C273B, which is very strong Phase referencing is too fast for JODRELL1 All targets are strong Schedule for MEDICINA (Code Mc ) Page 2 Snapshot Ionospheric Testing Observations UP: D => Below limits; H => Below horizon mask. blank => Up. Early: Seconds between end of slew and start. Dwell: On source seconds. Tapes: Drive, Index, Start footage / Direction, Head Group, End footage. TPStart: Tape motion start time. Frequencies are LO sum (band edge). ---------------------------------------------------------------------------------------- Start UT Source Start / Stop Early Tapes TPStart Stop UT LST EL AZ HA UP ParA Dwell (see above) ---------------------------------------------------------------------------------------- --- Thu 2 Jun 2005 Day 153 --- Next scan frequencies: 1637.99 1637.99 1645.99 1645.99 1653.99 1653.99 1661.99 1661.99 Next BBC frequencies: 342.99 342.99 350.99 350.99 358.99 358.99 366.99 366.99 Next scan bandwidths: 8.00 8.00 8.00 8.00 8.00 8.00 8.00 8.00 16 00 00 3C273B 09 31 28 32.2 484.1 -3.0 -36.2 0 1 1 0 16 00 00 16 05 20 --- 09 36 49 33.0 485.4 -2.9 -35.5 320 F 1 0 16 08 20 J1215-1731 09 39 50 18.4 500.7 -2.6 -28.3 146 1 1 0 16 08 20 16 09 20 =1213-172 09 40 50 18.6 500.9 -2.6 -28.1 60 F 1 0 16 09 20 J1212-2221 09 40 50 14.7 504.1 -2.5 -26.9 -12 1 1 0 16 09 20 16 11 00 =1209-220 09 42 30 14.8 504.4 -2.5 -26.7 88 F 1 0 16 11 00 J1215-1731 09 42 30 18.7 501.3 -2.6 -27.9 -12 1 1 0 16 11 00 16 12 40 =1213-172 09 44 10 18.9 501.7 -2.5 -27.6 88 F 1 0 16 12 40 J1212-2221 09 44 10 15.0 504.8 -2.5 -26.4 -12 1 1 0 16 12 40 16 14 20 =1209-220 09 45 51 15.2 505.1 -2.4 -26.2 88 F 1 0 16 14 20 J1215-1731 09 45 51 19.1 502.0 -2.5 -27.4 -12 1 1 0 16 14 20 16 16 00 =1213-172 09 47 31 19.3 502.4 -2.5 -27.1 88 F 1 0 16 16 00 J1159-2148 09 47 31 17.0 507.9 -2.2 -24.1 -11 1 1 0 16 16 00 16 18 00 =1157-215 09 49 31 17.2 508.4 -2.2 -23.8 109 F 1 0 16 18 00 J1215-1731 09 49 31 19.5 502.9 -2.4 -26.8 -11 1 1 0 16 18 00 16 20 00 =1213-172 09 51 32 19.7 503.3 -2.4 -26.5 109 F 1 0 16 20 00 J1159-2148 09 51 32 17.4 508.8 -2.1 -23.4 -11 1 1 0 16 20 00 16 22 00 =1157-215 09 53 32 17.6 509.3 -2.1 -23.1 109 F 1 0 16 22 00 J1215-1731 09 53 32 19.9 503.8 -2.4 -26.2 -11 1 1 0 16 22 00 16 24 00 =1213-172 09 55 32 20.1 504.2 -2.3 -25.9 109 F 1 0 16 25 00 J1159-2148 09 56 32 17.9 509.9 -2.1 -22.6 48 1 1 0 16 25 00 16 26 00 =1157-215 09 57 33 18.0 510.2 -2.0 -22.5 60 F 1 0 16 26 00 J1212-2221 09 57 33 16.3 507.7 -2.2 -24.3 -8 1 1 0 16 26 00 16 27 40 =1209-220 09 59 13 16.5 508.1 -2.2 -24.1 92 F 1 0 Schedule for MEDICINA (Code Mc ) Page 3 Snapshot Ionospheric Testing Observations UP: D => Below limits; H => Below horizon mask. blank => Up. Early: Seconds between end of slew and start. Dwell: On source seconds. Tapes: Drive, Index, Start footage / Direction, Head Group, End footage. TPStart: Tape motion start time. Frequencies are LO sum (band edge). ---------------------------------------------------------------------------------------- Start UT Source Start / Stop Early Tapes TPStart Stop UT LST EL AZ HA UP ParA Dwell (see above) ---------------------------------------------------------------------------------------- --- Thu 2 Jun 2005 Day 153 --- 16 27 40 J1159-2148 09 59 13 18.1 510.5 -2.0 -22.2 -8 1 1 0 16 27 40 16 29 20 =1157-215 10 00 53 18.3 510.9 -2.0 -21.9 92 F 1 0 16 29 20 J1212-2221 10 00 53 16.7 508.4 -2.2 -23.8 -8 1 1 0 16 29 20 16 31 00 =1209-220 10 02 33 16.8 508.8 -2.2 -23.6 92 F 1 0 16 31 00 J1159-2148 10 02 33 18.4 511.3 -2.0 -21.6 -8 1 1 0 16 31 00 16 32 40 =1157-215 10 04 14 18.5 511.7 -1.9 -21.4 92 F 1 0 16 32 40 J1212-2221 10 04 14 17.0 509.2 -2.1 -23.3 -8 1 1 0 16 32 40 16 34 20 =1209-220 10 05 54 17.1 509.5 -2.1 -23.0 92 F 1 0 16 34 20 J1159-2148 10 05 54 18.7 512.1 -1.9 -21.1 -8 1 1 0 16 34 20 16 36 00 =1157-215 10 07 34 18.8 512.5 -1.9 -20.8 92 F 1 0 16 36 00 J1159-2228 10 07 34 18.3 512.9 -1.9 -20.6 -6 1 1 0 16 36 00 16 37 40 =1156-221 10 09 14 18.4 513.2 -1.8 -20.3 94 F 1 0 16 37 40 J1159-2148 10 09 14 19.0 512.8 -1.8 -20.5 -6 1 1 0 16 37 40 16 39 20 =1157-215 10 10 55 19.1 513.2 -1.8 -20.3 94 F 1 0 16 39 20 J1159-2228 10 10 55 18.5 513.6 -1.8 -20.1 -6 1 1 0 16 39 20 16 41 00 =1156-221 10 12 35 18.7 514.0 -1.8 -19.8 94 F 1 0 16 41 00 J1159-2148 10 12 35 19.2 513.6 -1.8 -20.0 -6 1 1 0 16 41 00 16 42 40 =1157-215 10 14 15 19.4 514.0 -1.8 -19.7 94 F 1 0 16 42 40 J1159-2228 10 14 15 18.8 514.4 -1.8 -19.5 -6 1 1 0 16 42 40 16 44 20 =1156-221 10 15 56 18.9 514.8 -1.7 -19.2 94 F 1 0 16 44 20 J1159-2148 10 15 56 19.5 514.4 -1.7 -19.4 -6 1 1 0 16 44 20 16 46 00 =1157-215 10 17 36 19.6 514.8 -1.7 -19.1 94 F 1 0 16 47 40 3C273B 10 19 16 38.7 496.5 -2.2 -29.4 57 1 1 0 16 47 40 16 55 40 --- 10 27 17 39.7 498.7 -2.0 -28.1 480 F 1 0 16 58 40 J1224+0330 10 30 18 41.8 499.9 -1.9 -27.4 171 1 1 0 16 58 40 16 59 40 =1222+037 10 31 18 41.9 500.2 -1.9 -27.2 60 F 1 0 16 59 40 J1222+0413 10 31 18 42.8 500.6 -1.9 -27.0 -6 1 1 0 16 59 40 17 01 20 =1219+044 10 32 58 43.0 501.1 -1.8 -26.7 94 F 1 0 17 01 20 J1224+0330 10 32 58 42.1 500.7 -1.9 -26.9 -6 1 1 0 17 01 20 17 03 00 =1222+037 10 34 39 42.3 501.3 -1.8 -26.6 94 F 1 0 Schedule for MEDICINA (Code Mc ) Page 4 Snapshot Ionospheric Testing Observations UP: D => Below limits; H => Below horizon mask. blank => Up. Early: Seconds between end of slew and start. Dwell: On source seconds. Tapes: Drive, Index, Start footage / Direction, Head Group, End footage. TPStart: Tape motion start time. Frequencies are LO sum (band edge). ---------------------------------------------------------------------------------------- Start UT Source Start / Stop Early Tapes TPStart Stop UT LST EL AZ HA UP ParA Dwell (see above) ---------------------------------------------------------------------------------------- --- Thu 2 Jun 2005 Day 153 --- 17 03 00 J1222+0413 10 34 39 43.2 501.6 -1.8 -26.4 -6 1 1 0 17 03 00 17 04 40 =1219+044 10 36 19 43.4 502.1 -1.8 -26.1 94 F 1 0 17 04 40 J1224+0330 10 36 19 42.5 501.8 -1.8 -26.2 -6 1 1 0 17 04 40 17 06 20 =1222+037 10 37 59 42.7 502.3 -1.8 -25.9 94 F 1 0 17 06 20 J1222+0413 10 37 59 43.6 502.6 -1.7 -25.7 -6 1 1 0 17 06 20 17 08 00 =1219+044 10 39 39 43.8 503.1 -1.7 -25.4 94 F 1 0 17 08 00 J1224+0330 10 39 39 42.9 502.8 -1.8 -25.6 -6 1 1 0 17 08 00 17 09 40 =1222+037 10 41 20 43.0 503.3 -1.7 -25.3 94 F 1 0 17 09 40 J1218-0119 10 41 20 39.2 507.8 -1.6 -22.3 -12 1 1 0 17 09 40 17 11 20 =1216-010 10 43 00 39.4 508.3 -1.6 -22.0 88 F 1 0 17 11 20 J1224+0330 10 43 00 43.2 503.8 -1.7 -24.9 -12 1 1 0 17 11 20 17 13 00 =1222+037 10 44 40 43.4 504.3 -1.7 -24.6 88 F 1 0 17 13 00 J1218-0119 10 44 40 39.6 508.8 -1.6 -21.7 -12 1 1 0 17 13 00 17 14 40 =1216-010 10 46 21 39.7 509.3 -1.5 -21.3 88 F 1 0 17 14 40 J1224+0330 10 46 21 43.6 504.9 -1.6 -24.3 -12 1 1 0 17 14 40 17 16 20 =1222+037 10 48 01 43.7 505.4 -1.6 -23.9 88 F 1 0 17 20 40 J1636+2112 10 52 22 17.4 437.1 -5.7 -48.2 165 1 1 0 17 20 40 17 21 40 =1634+213 10 53 22 17.5 437.2 -5.7 -48.2 60 F 1 0 17 21 40 J1644+1813 10 53 22 14.1 438.2 -5.9 -47.3 -12 1 1 0 17 21 40 17 23 20 =1642+183 10 55 02 14.4 438.4 -5.8 -47.3 88 F 1 0 17 23 20 J1636+2112 10 55 02 17.8 437.5 -5.7 -48.3 -12 1 1 0 17 23 20 17 25 00 =1634+213 10 56 42 18.1 437.8 -5.7 -48.4 88 F 1 0 17 25 00 J1644+1813 10 56 42 14.7 438.7 -5.8 -47.4 -12 1 1 0 17 25 00 17 26 40 =1642+183 10 58 23 15.0 439.0 -5.8 -47.5 88 F 1 0 17 26 40 J1636+2112 10 58 23 18.4 438.0 -5.6 -48.4 -12 1 1 0 17 26 40 17 28 20 =1634+213 11 00 03 18.7 438.3 -5.6 -48.5 88 F 1 0 17 28 20 J1644+1813 11 00 03 15.3 439.3 -5.8 -47.5 -12 1 1 0 17 28 20 17 30 00 =1642+183 11 01 43 15.5 439.6 -5.7 -47.6 88 F 1 0 17 30 00 J1636+2112 11 01 43 19.0 438.6 -5.6 -48.6 -11 1 1 0 17 30 00 17 31 40 =1634+213 11 03 23 19.3 438.9 -5.6 -48.6 89 F 1 0 Schedule for MEDICINA (Code Mc ) Page 5 Snapshot Ionospheric Testing Observations UP: D => Below limits; H => Below horizon mask. blank => Up. Early: Seconds between end of slew and start. Dwell: On source seconds. Tapes: Drive, Index, Start footage / Direction, Head Group, End footage. TPStart: Tape motion start time. Frequencies are LO sum (band edge). ---------------------------------------------------------------------------------------- Start UT Source Start / Stop Early Tapes TPStart Stop UT LST EL AZ HA UP ParA Dwell (see above) ---------------------------------------------------------------------------------------- --- Thu 2 Jun 2005 Day 153 --- 17 31 40 J1641+2257 11 03 23 19.6 436.7 -5.6 -48.9 -7 1 1 0 17 31 40 17 33 20 =1639+230 11 05 04 19.9 437.0 -5.6 -49.0 93 F 1 0 17 33 20 J1636+2112 11 05 04 19.6 439.1 -5.5 -48.7 -7 1 1 0 17 33 20 17 35 00 =1634+213 11 06 44 19.9 439.4 -5.5 -48.7 93 F 1 0 17 35 00 J1641+2257 11 06 44 20.2 437.2 -5.6 -49.0 -7 1 1 0 17 35 00 17 36 40 =1639+230 11 08 24 20.5 437.5 -5.6 -49.1 93 F 1 0 17 36 40 J1636+2112 11 08 24 20.2 439.7 -5.5 -48.8 -7 1 1 0 17 36 40 17 38 20 =1634+213 11 10 04 20.5 439.9 -5.4 -48.9 93 F 1 0 17 38 20 J1641+2257 11 10 04 20.8 437.8 -5.5 -49.2 -7 1 1 0 17 38 20 17 40 00 =1639+230 11 11 45 21.1 438.0 -5.5 -49.2 93 F 1 0 17 41 00 J1636+2112 11 12 45 20.9 440.4 -5.4 -48.9 53 1 1 0 17 41 00 17 41 40 =1634+213 11 13 25 21.0 440.5 -5.4 -49.0 40 F 1 0 17 41 40 J1642+2523 11 13 25 22.7 436.1 -5.5 -50.0 -10 1 1 0 17 41 40 17 43 20 =1640+254 11 15 05 23.0 436.4 -5.5 -50.1 90 F 1 0 17 43 20 J1636+2112 11 15 05 21.3 440.8 -5.4 -49.0 -10 1 1 0 17 43 20 17 45 00 =1634+213 11 16 46 21.6 441.0 -5.3 -49.1 90 F 1 0 17 45 00 J1642+2523 11 16 46 23.3 436.6 -5.4 -50.2 -10 1 1 0 17 45 00 17 46 40 =1640+254 11 18 26 23.6 436.9 -5.4 -50.2 90 F 1 0 17 46 40 J1636+2112 11 18 26 21.9 441.3 -5.3 -49.1 -10 1 1 0 17 46 40 17 48 20 =1634+213 11 20 06 22.2 441.6 -5.3 -49.2 90 F 1 0 17 48 20 J1642+2523 11 20 06 23.9 437.2 -5.4 -50.3 -10 1 1 0 17 48 20 17 50 00 =1640+254 11 21 46 24.2 437.4 -5.4 -50.4 90 F 1 0 17 50 00 J1636+2112 11 21 46 22.5 441.9 -5.3 -49.2 -10 1 1 0 17 50 00 17 51 40 =1634+213 11 23 27 22.8 442.1 -5.2 -49.3 90 F 1 0 17 51 40 J1642+2523 11 23 27 24.4 437.7 -5.3 -50.4 -10 1 1 0 17 51 40 17 53 20 =1640+254 11 25 07 24.7 438.0 -5.3 -50.5 90 F 1 0 17 53 20 J1644+1813 11 25 07 19.7 443.5 -5.3 -48.2 -15 1 1 0 17 53 20 17 55 00 =1642+183 11 26 47 20.0 443.7 -5.3 -48.3 85 F 1 0 17 55 00 J1642+2523 11 26 47 25.0 438.2 -5.3 -50.6 -15 1 1 0 17 55 00 17 56 40 =1640+254 11 28 27 25.3 438.5 -5.2 -50.6 85 F 1 0 Schedule for MEDICINA (Code Mc ) Page 6 Snapshot Ionospheric Testing Observations UP: D => Below limits; H => Below horizon mask. blank => Up. Early: Seconds between end of slew and start. Dwell: On source seconds. Tapes: Drive, Index, Start footage / Direction, Head Group, End footage. TPStart: Tape motion start time. Frequencies are LO sum (band edge). ---------------------------------------------------------------------------------------- Start UT Source Start / Stop Early Tapes TPStart Stop UT LST EL AZ HA UP ParA Dwell (see above) ---------------------------------------------------------------------------------------- --- Thu 2 Jun 2005 Day 153 --- 17 56 40 J1644+1813 11 28 27 20.3 444.0 -5.3 -48.3 -15 1 1 0 17 56 40 17 58 20 =1642+183 11 30 08 20.6 444.3 -5.3 -48.3 85 F 1 0 17 58 20 J1642+2523 11 30 08 25.6 438.7 -5.2 -50.7 -15 1 1 0 17 58 20 18 00 00 =1640+254 11 31 48 25.9 439.0 -5.2 -50.8 85 F 1 0 SETUP FILE INFORMATION: NOTE: If DOPPLER, FREQ, or BW were used, see the individual scans for the final BBC settings. Setup file: eo999.18cm Matches group mc18cm in /aps3/sched/catalogs/freq.dat updated from Maccaferri (CR 2Dec00) Setup group: 5 Station: MEDICINA Total bit rate: 256 Format: MKIV1:2 Bits per sample: 2 Sample rate: 16.000 Number of channels: 8 Passes/head pos: 1 Speedup factor: 1.00 1st LO= 1295.00 1295.00 1295.00 1295.00 1295.00 1295.00 1295.00 1295.00 Net SB= U U U U U U U U Pol. = RCP LCP RCP LCP RCP LCP RCP LCP BBC = 2 1 4 3 6 5 8 7 BBC SB= U U U U U U U U IF = 2N 1N 2N 1N 2N 1N 2N 1N The following frequency sets based on this setup were used. Frequency Set: 5 Setup file default. No pcal detection. LO sum= 1637.99 1637.99 1645.99 1645.99 1653.99 1653.99 1661.99 1661.99 BBC fr= 342.99 342.99 350.99 350.99 358.99 358.99 366.99 366.99 Bandwd= 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 Track assignments are: track1= 2, 10, 18, 26, 3, 11, 19, 27 barrel=roll_off SOURCE LIST -- Snapshot Ionospheric Testing Observations Catalog positions marked with *. Precession of date coordinates is based on stop time of first scan. Names used in schedule marked with *. Short names used in VLA and SNAP files marked with +. Observation date used in B1950/J2000 coordinate conversion (PRECDATE): 1979.900 No adjustments are made for rates (DRA, DDEC). Scan hours are for recording scans only. Baseline hours are only counted for scans above horizon at both ends. Source Source position (RA/Dec) Error (B1950) (J2000) (Date) (mas) * J1159-2148 11 57 18.309811 * 11 59 51.906111 12 00 08.364401 0.27 1157-215 -21 32 11.49992 *-21 48 53.70757 -21 50 49.17241 0.78 J1159-21 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.250 scan hours, 8.429 baseline hours above horizon. * J1159-2228 11 56 37.757633 * 11 59 11.267254 11 59 27.707413 0.35 1156-221 -22 11 54.71372 *-22 28 36.90237 -22 30 32.54328 0.94 J1159-22 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.083 scan hours, 2.594 baseline hours above horizon. * J1212-2221 12 09 28.653794 * 12 12 03.697609 12 12 20.379490 0.31 1209-220 -22 05 10.38854 *-22 21 51.51342 -22 23 47.29736 0.86 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.139 scan hours, 3.385 baseline hours above horizon. * J1215-1731 12 13 11.668001 * 12 15 46.751756 12 16 03.492656 0.21 1213-172 -17 15 05.20060 *-17 31 45.40297 -17 33 39.75883 0.31 J1215-17 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.139 scan hours, 5.260 baseline hours above horizon. * J1218-0119 12 16 01.062434 * 12 18 34.929793 12 18 51.681004 0.28 1216-010 -01 03 15.08668 *-01 19 54.34138 -01 21 43.60871 0.52 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.056 scan hours, 1.312 baseline hours above horizon. * J1222+0413 12 19 49.255029 * 12 22 22.549619 12 22 39.310892 0.30 1219+044 04 29 53.60837 * 04 13 15.77616 04 11 28.33343 0.20 J1222+04 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.083 scan hours, 3.206 baseline hours above horizon. * J1224+0330 12 22 19.097168 * 12 24 52.421934 12 25 09.193350 0.31 1222+037 03 47 27.06610 * 03 30 50.29295 03 29 02.64562 0.24 J1224+03 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.156 scan hours, 6.701 baseline hours above horizon. J1229+0203 12 26 33.245835 * 12 29 06.699731 12 29 23.494262 0.30 1226+023 02 19 43.30564 * 02 03 08.59814 02 01 20.55370 0.20 3C273 /aps3/sched/catalogs/sources.vlba * 3C273B VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro J1229+02 0.222 scan hours, 12.119 baseline hours above horizon. * J1636+2112 16 34 28.653965 * 16 36 38.183456 16 36 53.384673 0.32 1634+213 21 18 56.44171 * 21 12 55.59502 21 12 08.41352 0.49 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.250 scan hours, 9.638 baseline hours above horizon. * J1641+2257 16 39 18.102927 * 16 41 25.227565 16 41 40.195915 0.24 1639+230 23 02 45.20241 * 22 57 04.03274 22 56 18.77175 0.43 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.083 scan hours, 2.867 baseline hours above horizon. * J1642+2523 16 40 36.555202 * 16 42 40.411845 16 42 55.070604 0.32 1640+254 25 28 43.57693 * 25 23 07.68189 25 22 22.98514 0.55 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.167 scan hours, 5.537 baseline hours above horizon. * J1644+1813 16 42 39.489851 * 16 44 52.432452 16 45 07.953357 0.84 1642+183 18 18 44.38577 * 18 13 17.23767 18 12 33.20535 1.82 /aps3/sched/catalogs/sources.vlba VLBA Calib Srcs - GSFC sols. - catalog 2004f_astro 0.139 scan hours, 3.457 baseline hours above horizon. The solar corona can cause unstable phases for sources too close to the Sun. SCHED provides warnings at individual scans for distances less than 10 degrees. The distance from the Sun to each source in this schedule is: Source Sun distance (deg) J1159-2148 115.1 J1159-2228 115.1 J1212-2221 118.0 J1215-1731 117.5 J1218-0119 112.6 J1222+0413 111.1 J1224+0330 112.0 3C273B 113.6 J1636+2112 136.5 J1641+2257 134.8 J1642+2523 132.4 J1644+1813 139.5 Barry Clark estimates from predictions by Ketan Desai of IPM scattering sizes that the Sun will cause amplitude reductions on the longest VLBA baselines at a solar distance of 60deg F^(-0.6) where F is in GHz. For common VLBI bands, this is: 327 MHz 117. deg 610 MHz 81. deg 1.6 GHz 45. deg 2.3 GHz 36. deg 5.0 GHz 23. deg 8.4 GHz 17. deg 15.0 GHz 12. deg 22.0 GHz 9. deg 43.0 GHz 6. deg