Hartebeesthoek (Hh) 2004 Report


Mark5A Recorder:

HartRAO took delivery of a Mark5A recorder in October 2003 together with
components for some 20 disc-packs including 160 x 180GB disks destined for
the IVS geodetic pool.  Of these, some 15 disc-packs have been assembled
and 10 sent to various correlators.  Early in March we ordered from Conduant
a further 20 disc-packs populated with 160GB disks, which hopefully will
be delivered in time for use in the May session.

We have just been authorised to use our Mark5A as the primary recorder for
all future geodetic experiments.


Mark 4 Terminal:

Towards the end of the February 2004 session we corrected the TPI zero
levels in both upper and lower sideband of all our video converters. 
We also replaced a faulty resistor which caused the gain of the TPI circuit
in VC07 to be 1/5 of normal.  Together these changes enable the "ifadjust"
command to set the IFD attenuators automatically.

However in re-seating all the video converters, one coaxicon pin came loose
in the connector at the back of VC01, resulting in the loss of VC01 USB as
reported in N04L1 (and subsequently by both Bonn and Washington correlators).
This has now been fixed.  However we have no explanation for why there were
no fringes on Headstack 2 in N04L1, whereas both N04X1 and N04C1 did have
fringes on both headstacks and no cables were changed between them and N04L1.
The problem is not traceable to our re-seating of video converters as the
health of all other VCs has subsequently been verified by the correlators.


Frequency Standards:

HartRAO took delivery of a new EFOS-C maser (EFOS-28) from Observatoire
Neuchatel in September 2004 which has replaced EFOS-6 as our primary time
standard and VLBI frequency reference.  We are still in the process of
determining the viability of re-furbishing EFOS-6 since Q measurements
revealed that its storage bulb is still in good condition.


Telescope Surface:

All surface panels on our 26m antenna have now been replaced with solid
panels with estimated 150um rms surface accuracy.  We are now in the process
of shifting the panels to their correct locations (as the panel-mounting
brackets were also replaced) prior to optically setting them to the correct
heights.  A MEng student has recently joined us with the problem of setting
panels using single-dish holography on satellites as his thesis project.


Receivers:

No changes to receivers have been made over th period since the last TOG
meeting.  We are currently investigating the possibilities for crygonic
amplifiers for a possible new 22 GHz dual-polarisation receiver.