Proposal of a four-band test at the end of rdv35 VLBI experiment

Proposal of a four-band test at the end of rdv35 VLBI experiment

(Revision #1)

Three additional scans of quasi-simultaneous observations at X/S, U (2 cm) and K (1 cm) bands and one additional scans of observing in lower and upper ends of K and U bands are proposed to add to the end of rdv35 experiment on 2002.09.25.

Objectives of the test:

To estimate the errors of ionosphere contribution. When we have more than two bands, we have redundant information and this redundancy can be used for assessments of accuracy.

To demonstrate that quasi-simultaneous multi-band observations at high frequencies are feasible.

To demonstrate that observations with fast switching between the wings of U and K bands at VLBA are feasible. Can the phases at upper and lower wings of the band be aligned? Will be super-wide band delay over 2.5GHz more precise than the group delay over 0.5GHz?

VLBA antennas have an ability to switch quickly between receivers. It takes from 2 to 6 seconds to switch from X/S receivers to U (2 cm) and K-band (1 cm) receivers. Besides, although VLBA antennas can record simultaneously signal only within 500 MHz bandwidth, they can quickly (for less than <1 sec) siwtch between the wings of the receiver band.

I propose to add 3 additional scans to the end of rdv35 experiment and to observe three strong sources at 10 VLBA antennas.

       --         --        --   2cm, 8 channels
     -    -    --    -    -      1cm, 8 channels
  --        --         --        13/4 cm, 4 and 4 channels
 |  g G  G g  g  G  G g  g G  |
  ---------------------------->  time
  scan

  - scan segment                              (15 sec)
  g switch time from 13/4 cm to 1 cm receiver ( 3 sec)
  G switch time from    1 cm to 2 cm receiver ( 4 sec)

Antennas observe 20 sec at X/S bands, then receivers move to 1 cm, observe 10 sec, then move to 2 cm, observe 20 sec. Then receivers move the same way back. Scan duration is 5 min 05 sec. Integration time is 90 sec in each band. Bandwidth at 1 and 2 cm is twice greater than the band at 13/4 cm. This will compensate loss of sensitivity at 1 and 2 cm with respect to 4 cm.

I propose to use v2cm_d2 frequency at 2 cm band and v1cm_b9 frequency at 1 cm band.

In addition to these three scans I propose to add the 4-th scan for observing at the wings of 1 and 2 cm receivers:

     ul    ul    ul  2 cm
  ul    ul    ul     1 cm
 |  G  G  G  G  G  |
  -----------------> time

  u  scan segment at upper end of the band (30 sec)
  l  scan segment at lower end of the band (30 sec)
  G  switch time from 1 to 2 cm receiver   ( 4 sec)

Scan duration: 6 min 20sec. Integration time: 90 sec. I propose to observe the same source in scan 4 as in scan 3.

I propose to use v2cm_a3 and v2cm_d2 frequencies at 2 band cm; v1cm_a2 and v1cm_b9 frequencies at 1 band cm.

Frequencies for 2 cm band:

Name = v2cm_a3  Station = VLBA    Priority = 0
  rf1    = 12100, 12100   ifname = B,    D
  rf2    = 12600, 12600   fe     = '2cm', '2cm'
  pol    = RCP,   LCP     lo1    = 11600, 11600   syn(1) = 11.6
  ch1rf1 = 11900, 11900   ch1rf2 = 12900, 12900 
  note   = 'First 2cm filter'

Name = v2cm_d2  Station = VLBA    Priority = 0
  rf1    = 14900, 14900   ifname = B,    D
  rf2    = 15400, 15400   fe     = '2cm', '2cm'
  pol    = RCP,   LCP     lo1    = 14400, 14400   syn(1) = 14.4
  ch1rf1 = 14900, 14900   ch1rf2 = 15900, 15900 
  note   = 'Fourth 2cm filter'

Frequencies for 1 cm band:

Name = v1cm_a2  Station = VLBA    Priority = 0
  rf1    = 21500, 21500   ifname = B,    D
  rf2    = 22000, 22000   fe     = '1cm', '1cm'   syn(1) = 8.9 
  pol    =   RCP,   LCP   lo1    = 21000, 21000   syn(3) = 12.1

Name = v1cm_b9  Station = VLBA    Priority = 0
  rf1    = 23500, 23500   ifname = B,    D
  rf2    = 24000, 24000   fe     = '1cm', '1cm'   syn(1) = 9.1
  pol    =   RCP,   LCP   lo1    = 23000, 23000   syn(3) = 13.9

I propose to use 8 IF channels for 1 cm, 2 cm scans and not to change these frequencies. The IF frequency setup at X/S bands is the same as for the previous rdv experiments.

I propose to use accumulation period length 0.262 seconds in order to minimize data losses during frequency band switching and in order to learn actual duration of gaps.

Three sources should be selected in different regions of the sky in order to have some scans at low elevations and some scans at high elevations.

Proposed test requires additional 20 minutes of observations.

I would like to thank Criag Walker for useful discussion whcih stimulated this proposal.

Back to Leonid Petrov's discussion page.

Last update: 14-AUG-2002 16:56:57