VLA/VHF Program Update 2005 May 13 Recent and Upcoming Events April 27 Successful testing of 1 MHz filter assemblies to damp TV carriers and establish stable auto-level control in the VLA electronics. May 11 Installation of third and fourth prototype receivers on antennas 8 (W4) and 26 (N12). Work completed in just one day! May 18 Test shutdown of KNMD-TV (Ch. 9) to assess usefulness of future coordination. First attempt to obtain phase closure. Further night-time and day-time testing of system performance in total power. June 1 Deadline for submission of an observing proposal for the second D- configuration, in early 2007. 150 hours have been approved for the next D-configuration, following peer review and subject to final project review and successful testing. Socorro Travel April 26-29 Greenhill May 9-13 Greenhill, Kimberk May 17-21 Greenhill Notes and Details Work in April showed that the VLA IF system is badly affected by rapid time variability of TV carriers. Proper operation is not possible w/o filtering. Identification of Tin Lee (Toronto) as a vendor of tunable 1 MHz filters has enabled us to obtain stable operation for testing (currently at 195.4 MHz). The filters are used in series. Four are available, permitting operation in one polarization on one baseline. Four more are due for delivery next week. Total power measurements to obtain Tsys and antenna efficiency have been unsuccessful thus far because there is interference between the Tcal signals within the first two receivers, where the output of one noise diode is injected into each polarization channel before the Q-hybrid. Proper measurement has been anticipated once the second pair of receivers, which use separate noise diodes for each channel have been installed and tested. The second pair of receivers has tested "perfectly" on the bench. The Tcal values and gains between channels and receivers is about the same. After installation, initial testing has shown that when connected to the dipole feeds at the antenna foci, the receiver temperatures or injected cal power is substantially unequal. An in depth investigation in the field will be required.