Shanghai VLBI Station report  
    (Nov. 29, 2005)


1. Observations

During 2005 the Shanghai VLBI Station (also called SESHAN25) participated in 36 experiments 
(including Network Mornitoring Experiments and antenna amplitude calibration experiments) 
organized by the EVN, as well as 17 geodetic experiments coordinated by the IVS for geodetic 
purposes. Except for routine EVN and IVS VLBI sessions, the Shanghai VLBI Station also took 
part in a number of coordinated observations together with radio telescopes in Japan and Australia. 


2. Development and maintenance activities in 2005

2.1 Update of the antenna control system of the SESHAN25 telescope.

We have updated the antenna control system in August 2005. The new control system is  more flexible 
than the old one. It is expected to realize fast slewing, accurate tracking and minimize observation 
problems due to antenna tracking. The new system run in a good state in Oct'05 EVN sessions. General 
descriptions of the new control system are given in detail: 
Azimuth slewing rate : 1degree/second           (after September 2005)
Azimuth slewing range: -78 degree to 430 degree (after September 2005)
Elevation slewing rate : 0.6degree/second       (after September 2005)
Elevation slewing range: 5degree to 88.5 degree (after September 2005)

2.2 Installation of a new, cryogenically cooled L band receiver.

A new L band receiver with cryogenically dual-circular-polarized front-end was designed and developed 
in the ASTRON in Dwingeloo and at the Shanghai VLBI Station.  The new L band receiver was installed 
at the SESHAN25 telescope in September 2005.  It has replaced the old one and has been playing full 
role in the past Oct'05 EVN sessions. Quick responses from the NME experiment at L band (N05L5) showed 
that the polarizations at the Shanghai station has swapped. We adjusted the patching of LHCP and RHCP 
starting from session EK022B. Actually the problem is associated with the optical path system at the 
SESHAN25 telescope, not with the receiver itself.  

2.3 Adjustment of antenna panels

The main reflector of the SESHAN25 telescope has been adjusted using the holography surveys in 
5--18 November 2005. This activity was done with the help of Mr. Michael Kesteven. 

Before holography measurements, the surface accuracy (rms) was about 1.2 mm. Much of it was confined 
to one quadrant. The amplitude distribution in the aperture plane shown in the holography results was 
not symmetrical: the centroid was about 3m from the optical axis. The subreflector was deviated from 
the optical axis (as defined by the outer ring of panels) by 15mm and was also tilted by several 
degrees from the optical axis - equivalent to an additional shift.

The adjustments were completed on 18 November 2005. All evidences now show that the performance has 
been improved, based on the holography data and the sidelobe patterns. The subreflector was centralised, 
it only tilted by a small amount now. The magnitude was directed by the hololgraphy;  it was confirmed 
by the appearance of fairly symmetric sidelobes. The final surface accuracy (rms) is about 0.55 mm.

2.4 Testing performance of the new H-maser MHM-2010.  
A new H-maser (MHM-2010) was first used in July 2004. It has been running well for more than one year. 
We tested its performance including frequency stability and accuracy in July 2005. The results from 
testing indicate that it matches the performance specifications and is working in good condition 
(The attached plots exhibit the testing results). 

2.5 Changes in the recording system (REC)
There are only eight BBC's (BBC01 to BBC08) and one IF distributor available at the Shanghai VLBI 
Station since September 2005. (The other six BBC's and one IF Distributor have been used for tesing 
the new-built Beijing 50m telescope) 

A new power supply of Mark 5A (for two disk banks with 250G) will be installed and tested in Novermber 2005.
	
We kept updating the FS software system with the latest version. The current version 9.7.7 in use works well 
at the Shanghai VLBI Station. The Mark 5A recording system also works well in IVS and EVN sessions. We have 
bought a spare SWT FS computer.

3. Further plans
 
3.1 New S/X band feed and receiver. 
A new S/X band feed will be fixed in December 2005.
A set of new S/X receivers are in development and will be available in the middle of 2006.

3.2 Fibre link 
Contracts of fiber link communication have been completed. The fiber cable with 1Gbps rate will link between the 
Shanghai VLBI Station and the headquater of SHAO. The project will soon start and is expected to finished 
in Spring 2006.