Navigating Across the C-band

The US Naval Observatory makes daily UT1 Intensive observations on the Mauna Kea-Pie Town (MkPt) baseline of the Very Long Baseline Array (VLBA) using the standard S/X bands in a bandwidth synthesis mode. These observations are increasingly negatively impacted by RFI in the S-band. The frequency range of the S-band receiver is no more than 256 MHz wide, restricting the ability to place the 32 MHz wide channels to avoid the RFI. The VLBA C-band receiver is more sensitive and has a wide frequency range (3.9-7.9 GHz) which allows for more flexibility in the placement of channels. To see if the difficulties encountered in the S-band can be overcome by using the C-band, we have undertaken two experiments using the C-band receiver on the Hancock-Owens Valley baseline of the VLBA. The first is a standard group delay observing setup accomplished by placing channels at the low and high ends of the C-band frequency range as analogs of the S- and X-bands. A major question here is whether the smaller frequency separation is sufficient for ionosphere calibration. The second is an attempt at broadband group delay measurement across the width of the C-band. Here we present the design of these sessions and preliminary results.