Extensive VLBA recorder recording quality tests were performed in April 2000 to investigate the reason for poor thin tape recording quality. Especially the recording quality of upper tracks was poor. This was most likely caused by thin/thick tape switching. There were long runs of thick tape in a CMVA session a little before the EVN thin tape session in February.
After extensive recorder tests no definitive cause could be found. Re-contouring the head with abrasive tape and high (40%) humidity has apparently (according to thin tape test at JIVE correlator) alleviated the problem. Currently we are running thin tape at a vacuum level of 6 inches and thick tape at 28(!) inches of water.
The new Mark IV formatter and associated VIV upgrade items were installed in October and used succesfully in November sessions. The electronics and mechanical mounts for the second head will be installed after a second fully functional headstack is available.
Jouko Ritakari and Ari Mujunen have written several papers on the impact of the fast Ethernet connections to the VLBI. These documents can be found at the following address:
An initial investigation of modern monolithic PLL/synthesizer chips
was coducted as a possible replacement for VLBA BBC LO oscillators.
National Semiconductor ``PLLatinum'' series chips seem promising but a
suitable commercial VCO remains a problem with its 500
1000 MHz
frequency range requirement.
Prototypes for a ``Clodi'' 1pps multi-channel simultaneous sampling clock difference counter have been built. The basic high-speed, low-skew 1pps rising edge detector/comparator has been designed and tested in prototype. Based on a 100 MHz CPLD design, the counter chips have also been tested in a two-channel prototype setup with an embedded alphanumeric display. A multi-channel prototype with computer LPT port interface is being developed.