EVLA Frequency Bands and Tunability
For OSRO observations each receiver can tune to two different "baseband" frequencies from the same wavelength band. Right-hand circular (RCP) and left-hand circular (LCP) polarizations are received for both frequencies. Each of these four data streams currently follows the VLA nomenclature, and are known as IF (for "Intermediate Frequency" channel) "A", "B", "C", and "D". IFs A and B receive RCP, IFs C and D receive LCP. IFs A and C are always at the same frequency, as are IFs B and D (but the IFs A/C frequency is usually different from the B/D frequency). We normally refer to these two independent data streams as "IF pairs." Currently, a maximum of 1.024 GHz can be correlated for each IF pair (see Correlator Configurations), for a total maximum bandwidth of approximately 2 GHz.
The tuning ranges, along with default frequencies for continuum applications, are given in Table 7 below. At X-band a number of the antennas will continue to have the old narrow-band VLA X-band receivers until their retrofit is complete at the end of the EVLA construction project. As of December 2010 there is not a sufficient number of EVLA-style X-band receivers in the array to evaluate either the system performance or the radio frequency interference environment throughout the EVLA X-band tuning range of 8-12 GHz. A total bandwidth of 800 MHz equivalent to that of the VLA receivers (8.0-8.8 GHz) should be assumed for the purposes of sensitivity calculations at X-band for the present.
| Band | Range | Default frequencies for continuum applications (GHz) | |
|---|---|---|---|
| (GHz) | IFs A/C | IFs B/D | |
| 20 cm (L) | 1.0-2.0 | 1.251 | 1.751 |
| 13 cm (S) | 2.0-4.0 | 2.5 | 3.5 |
| 6 cm (C) | 4.0-8.0 | 5.0 | 6.0 |
| 3 cm (X) | 8.0-12.0 | 8.52 | 9.52 |
| 2 cm (Ku) | 12.0-18.0 | 13.5 | 14.5 |
| 1.3 cm (K) | 18.0-26.5 | 20.7 | 21.7 |
| 1 cm (Ka) | 26.5-40.0 | 31.5 | 32.5 |
| 0.7 cm (Q) | 40.0-50.0 | 40.5 | 41.5 |
- Notes:
- 1. This default frequency set-up for L-band comprises two 512 MHz basebands (each with 8 subbands of 64 MHz) to cover the entire 1-2 GHz of the L-band receiver.
- 2. Many of the antennas continue to have the old narrow-band VLA receivers (see Figure 1), for which a total bandwidth of 800 MHz should be assumed (8.0-8.8 GHz). The RFI environment of the default tunings has not yet been evaluated.
In general, for all frequency bands except Ka, if the total span of the two independent IFs (defined as the frequency difference between the lower edge of one IF pair and the upper edge of the other) is less than 8.0 GHz, there are no restrictions on the frequency placements of the two IF pairs. For Ka and Q bands (the only two bands where a span greater than 8 GHz is possible), there are special rules:
- At Ka band, the low frequency edge of the AC IF must be greater than 32.0 GHz. There is no restriction on the BD frequency.
- At Q band, if the frequency span is greater than 8.0 GHz, the BD frequency must be lower than the AC frequency.
