EVLA Frequency Bands and Tunability

The EVLA electronics and local-oscillator systems enable tuning over wider frequencies, which is possible with the wideband feeds being installed on retrofitted antennas (or already present at K and Q bands). At this writing, wider-band tuning capabilities are available at L, C, K, and Q bands (mostly with interim EVLA receivers at L and C bands), and the new 1.0 cm band will be available on at least 14 antennas in mid-2009. For example, the new C band tuning enables observations of methanol at 6.7 GHz, while the new K band tuning enables observations of the 22.235 GHz H$_2$O line at redshifts up to $z\approx 0.18$. Figure 3 shows the present plan for EVLA receiver deployment over the remainder of the EVLA Construction Project, while Table 8 gives a prediction of the new frequency capabilities that we expect in June 2009 and December 2009.

Figure 3: EVLA Receiver Deployment Plan. Above is a plot of the availability of the final EVLA receivers from 2008 until the end of the EVLA Construction Project in 2012. Only final EVLA receivers are shown. Interim receivers with reduced frequency coverage or polarization purity are available at some bands, and are shown in other figures. Approximate installation dates for 2-GHz and 8-GHz bandwidths per polarization also are shown, but these will not be accessible to observers until after the transition from the VLA correlator to the EVLA (WIDAR) correlator and the full commissioning of the new correlator.

Table 8: Tuning Ranges of EVLA Bands

Band	Range	Final EVLA Receivers Available
		June 2009	December 2009
20 cm (L)	1.2 - 2.0 GHz	3	7
13 cm (S)	2.0 - 4.0 GHz	4	7
6 cm (C)	4.0 - 8.0 GHz	11	17
3 cm (X)	8.0 - 12.0 GHz	0	0
2 cm (U)	12.0 - 18.0 GHz	1	2
1.3 cm (K)	18.0 - 26.5 GHz	22	22
1 cm (Ka)	26.5 - 40.0 GHz	15	21
0.7 cm (Q)	40.0 - 50.0 GHz	22	22

Note: The rightmost columns give the numbers of final EVLA receivers available at each band; additional interim receivers with poorer polarization purity are available in the 1-2 GHz and 4-8 GHz bands, while the old narrow-band VLA receivers are still available in the 8-8.8 GHz band.

Figure 3 does not tell the entire story of frequency availability for observing with the VLA, since there also are some interim receivers that may be used in the absence of the final EVLA receivers. Thus Figures 4 and 5 give more detailed schedules for each frequency band, including the presence of these interim receivers.

Figure 4: Low-frequency Receiver Availability. Above is a plot of the receiver availability at the four lowest-frequency EVLA bands, between 1 and 12 GHz, from 2008 through the end of 2012. For each plot, the red line shows the number of old VLA receivers available, the light green line shows the availability of interim EVLA recievers (typically with increased bandwidth coverage but without optimal polarization performance), and the blue line shows the availability of final EVLA receivers.

Figure 5: High-frequency Receiver Availability. Above is a plot of the receiver availability at the four highest-frequency EVLA bands, between 12 and 50 GHz, from 2008 through the end of 2012. For each plot, the red line shows the number of old VLA receivers available, typically with more limited tuning capability, and the blue line shows the availability of final EVLA receivers.

The new Ka-band system is most sensitive around 33 GHz, and the default continuum frequency has been set to 33.5 GHz. The $K$ factor to be used in calculating expected sensitivities at the default continuum frequency is 20. The relative sensitivity as a function of frequency across the entire band is shown in Figure 6.

Figure 6: Ka-band sensitivity as a function of frequency.

IFs B and D are able to tune over the full 26.5 to 40 GHz, while IFs A and C cover 32-40 GHz. IFs B/D must also be tuned to a lower frequency than IFs A/C. For the EVLA Ka-band receivers it is possible to tune the two IF pairs up to 11 GHz apart, while for other EVLA receivers the IFs can be separated by the full tuning range. Please check with VLA staff before attempting observations outside the standard VLA tunings.