VLA Frequency Bands and Tunability

Bands

For observations taken with the 8-bit samplers, each receiver can tune to two different frequencies, each 1024 MHz wide, within the same frequency band. Right-hand circular (RCP) and left-hand circular (LCP) polarizations are received for both frequencies, except for the low-band receiver (50–500 MHz), which provides linear polarization (X and Y). Each of these four data streams follows the VLA nomenclature and are known as IF (for Intermediate Frequency channel) A, B, C, and D. IFs A and B provide RCP (or Y when applicable), IFs C and D provide LCP (or X when applicable). IFs A and C are always at the same frequency, as are IFs B and D (but note that the A and C IFs frequency is usually different from the B and D frequency). We normally refer to these two independent data streams as IF pairs, i.e., the A/C pair and the B/D pair. In 8-bit mode, a maximum of 1024 MHz can be correlated for each IF pair (see the WIDAR Section), for a total maximum bandwidth of 2048 MHz. To distinguish this 8-bit system from the 3-bit system, these IF pairs are denoted A0/C0 and B0/D0.

More options are available with the 3-bit samplers. This system provides four (R,L) polarization pairs, each 2048 MHz wide. The A/C IF pair provides two sampled pairs, labelled A1/C1 and A2/C2, and the B/D IF pair provides two sampled pairs, labelled B1/D1 and B2/D2.

For more details on the 8-bit and 3-bit samplers see the VLA Samplers section.

The tuning ranges, along with default frequencies for continuum applications, are given in Table 3.3.1 below.

Table 3.3.1: Default frequencies for continuum applications
Band Range1 8-bit continuum applications (GHz) 3-bit continuum applications (GHz)
  (GHz) IF pair A0/C0 IF pair B0/D0 IF pair A1/C1 IF pair A2/C2 IF pair B1/D1 IF pair B2/D2
4 m (4) 0.054 – 0.0842 — .070 – .082 — — — —
90 cm (P) 0.20 – 0.503 0.224 – 0.4803 — — — — —
4 m (4)/90 cm (P) 0.054 – 0.0842/
0.20 – 0.503		 0.224 – 0.4803 .070 – .082
20 cm (L) 1.0 – 2.04 1.0 – 1.54 1.5 – 2.04 — — — —
13 cm (S) 2.0 – 4.0 2.0 – 3.0 3.0 – 4.0 — — — —
6 cm (C) 4.0 – 8.0 4.5 – 5.5 5.5 – 6.5 4.0 – 6.0 6.0 – 8.0 — —
3 cm (X) 8.0 – 12.0 8.0 – 9.0 9.0 – 10.0 8.0 – 10.0 10.0 – 12.0 — —
2 cm (Ku) 12.0 – 18.0 13.0 – 14.0 14.0 – 15.0 12.0 – 14.0 14.0 – 16.0 — 16.0 – 18.0
1.3 cm (K) 18.0 – 26.5 20.2 – 21.2 21.2 – 22.2 22.0 – 24.0 24.0 – 26.0 18.0 – 20.0 20.0 – 22.0
1 cm (Ka) 26.5 – 40.0 32.0 – 33.0 31.0 – 32.0 33.0 – 35.0 35.0 – 37.0 29.0 – 31.0 31.0 – 33.0
0.7 cm (Q) 40.0 – 50.0 40.0 – 41.0 41.0 – 42.0 44.0 – 46.0 46.0 – 48.0 40.0 – 42.0 42.0 – 44.0

Notes:

1.  Listed here are the nominal band edges. For all bands, the receivers can be tuned to frequencies outside this range, but at the cost of diminished performance. Contact the NRAO Helpdesk for further information.
2. The 4-band system is currently under development. The default frequency range maximizes sensitivity of the system and provides a nominal bandwidth of 12 MHz and a channel resolution of 64 kHz.
3. The default setup for P-band will provide 16 subbands from the A0/C0 IF pair, each 16 MHz wide, to cover the frequency range 224–480 MHz. The channel resolution is 125 kHz. 
4. The default frequency setup for L-band comprises two 512 MHz IF pairs (each comprising 8 contiguous subbands of 64 MHz) to cover the entire 1–2 GHz of the L-band receiver.

 

Tuning Restrictions

In general, for all frequency bands except Ka, if the total span of the two independent IF pairs of the 8-bit system (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 K, Ka, and Q-bands—the only bands where a span greater than 8 GHz is possible—there are special rules:

  • At Ka-band, the low frequency edge of the A0/C0 IF pair must be greater than 32.0 GHz. There is no restriction on the B0/D0 frequency, unless the B0/D0 band overlaps the A0/C0 band when the latter is tuned at or near the 32.0 GHz limit. In this case, the Observation Preparation Tool (OPT) may not allow the requested frequency setups. Users wanting to use such a frequency setup are encouraged to contact the NRAO Helpdesk for possible tuning options.
  • At K and Q-bands, if the frequency span is greater than 8.0 GHz, the B0/D0 frequency must be lower than the A0/C0 frequency.

For the 3-bit system, the maximum frequency span permitted for the A1/C1 and A2/C2 IF pairs is about 5000 MHz. The same restriction applies to B1/D1 and B2/D2. The tuning restrictions given above for the separation and location of the 8-bit pairs A0/C0 and B0/D0 also apply to the 3-bit pairs, with A0/C0 replaced by A1/C1 and A2/C2, and B0/D0 replaced by B1/D1 and B2/D2.

 

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