FOREST (FOur-beam REceiver System on the 45-m Telescope)

Frontend

• Measurement results of Image Rejection Ratio (IRR):
  • Season 2023-2024 (measured on Oct.)
• Remarks:
  • All beams and polarisations should be the same frequency settings.
• Reference:
  • Minamidani, T.; Nishimura, A.; Miyamoto, Y.; Kaneko, H.; Iwashita, H.; Miyazawa, C.; Nishitani, H.; Wada, T.; Fujii, Y.; Takahashi, T.; Iizuka, Y.; Ogawa, H.; Kimura, K.; Kozuki, Y.; Hasegawa, Y.; Matsuo, M.; Fujita, S.; Ohashi, S.; Morokuma-Matsui, K.; Maekawa, J.; Muraoka, K,; Nakajima, T.; Umemoto, T.; Sorai, K.; Nakamura, F.; Kuno, N.; Saito, M.
    “Development of the New Multi-Beam 100 GHz Band SIS Receiver FOREST for the Nobeyama 45-m Telescope”
    Proceedings of SPIE, 9914, 99141Z (2016) /[ADS]
  • Minamidani, T.; Umemoto, T.; Nishimura, A.; Matsuo, M.; Fujita, S.; Tsuda, Y.; Ohashi, S.; Tosaki, T.; Kuno, N.
    “Nobeyama CO Galactic Plane Survey: New Chapter of the Nobeyama 45-m Telescope”
    Conditions and Impact of Star Formation. Edited by R. Simon, R. Schaaf and J. Stutzki. EAS Publications Series, Volume 75-76, pp.193-194 (2016)
    [ADS]
  • Muraoka, K.; Matsui, K.; Akashi, T.; Kuno, N.; Iwashita, H.; Miyazawa, C.; Koyano, M.; Baji, H.; Maekawa, J.; Nakajima, T.; Onodera, S.; Sakai, T.; Kimura, K.; Maezawa, H.; Onishi, T.; Ogawa, H.
    “Test Observations of a New 100 GHz Wave-Band FOur-beam REceiver System on the Nobeyama 45-m Telescope (FOREST)”, New Trends in Radio Astronomy in the ALMA Era: The 30th Anniversary of Nobeyama Radio Observatory, R. Kawabe, N. Kuno and Yamamoto, S., eds., ASP Conference Series 476, 417 (2013) [ADS]
  • Nakajima, T. et al.,
    “Development of a New Multi-Beam Array 2SB Receiver in 100 GHz Band for the NRO 45-m Radio Telescope”,
    Proceedings of ISSTT, P12 (2012) http://www.nrao.edu/meetings/isstt/papers/2012/2012105108.pdf

Detailed Information on Frequency Down-Conversions in FOREST and IF Chain

• RF (80 – 116 GHz) signals are down-converted to 4 – 12 GHz IFs with 2SB Mixers, and USB (upper sideband) and LSB (lower sideband) signals are obtained separately.
• Each 4 – 12 GHz IF signal is divided into two bands, low (4 – 8 GHz) and high (7 – 11 GHz), and the high band (7 – 11 GHz) is down-converted to 4 – 8 GHz using 15 GHz PLO.
• Therefore, all output signals from the FOREST are 4 – 8 GHz signal, labelled USB-L (USB: 4 – 8 GHz), USB-H (USB: 7 – 11 GHz), LSB-L (LSB: 4 – 8 GHz), and LSB-H (LSB: 7 – 11 GHz).
• See also schematic view in Figure 3.
• Further detailed information is described in Minamidani et al. (2016)

FOREST 4-Beam:

• Two (2) IF bands can be selected from these four (4) bands, and possible patterns are summarised in the table in Figure 4.
• Each selected 4 – 8 GHz IF band (IF-A (IF01 – 08) / IF-B (IF09 – 16)) are down-converted to 2 – 4 GHz band.
• See also schematic view and table in Figure 4.

FOREST 2-Beam On-On:

• Four (4) IF bands can be selected from four (4) bands, and possible patterns are summarised in the table in Figure 5: simultaneous use of USB-L and LSB-H is forbidden.
• Each selected 4-8 GHz IF band (IF-A1, IF-A2, IF-B1, IF-B2) are down-converted to 2-4 GHz band.
• See also schematic view and table in Figure 5.

FOREST 1-Beam (Singel-Beam):

• Four (4) IF bands can be selected from four (4) bands, and possible patterns are summarised in the table in Figure 6: simultaneous use of USB-L and LSB-H is forbidden.
• Each selected 4-8 GHz IF band (IF-A1, IF-A2, IF-B1, IF-B2) are down-converted to 2-4 GHz band.
• See also schematic view and table in Figure 6.

Backend

General Notes for FOREST Receiver

FOREST equips two IFs for both sidebands (USB-L, USB-H, LSB-L, and LSB-H). USB-L and LSB-L cover from 4 GHz to 8 GHz, while USB-H and LSB-H have a range of 7 GHz to 11 GHz.

Choosing an appropriate sample device file is a key for your successful observation. An easier way in choosing a sample file you should use is to calculate the difference between frequency of your target lines. Although the following table illustrates the concrete examples for FOREST non-SpW mode, a combination of IFs is the same for other scan modes that use FOREST receiver.

• 22 GHz > (Frequency difference) > 18 GHz:
  You can use whichever you like:
  fn_hvhv_ppmm_a.ndevice (LSB-H and USB-H)
  fn_hvhv_mmpp_a.ndevice (USB-H and LSB-H)
• 18 GHz > (Frequency difference) > 15 GHz:
  You can use whichever you like:
  fn_hvhv_llpp_a.ndevice (LSB-L and USB-H)
  fn_hvhv_ppll_a.ndevice (USB-H and LSB-L)
• 15 GHz > (Frequency difference) > 8 GHz:
  You can use whichever you like:
  fn_hvhv_lluu_a.ndevice (LSB-L and USB-L)
  fn_hvhv_uull_a.ndevice (USB-L and LSB-L)
• 8 GHz > (Frequency difference) > 7 GHz:
  Such lines cannot be observed simultaneously
• 7 GHz > (Frequency difference) > 4 GHz:
  The following four sample device files are candidates. Although there are little differnce between them, we recommend users to check the system noise temperature of FOREST (Figure 4 at Frontend status at the Status Report) and find better sideband at the target rest frequencies.
  For example, in the 2017-2018 observing season, Beam 1 H-polarisation LSB show higher system noise temperature at 87-95 GHz. This frequency range can also be observed with USB. In this case, observations with fn_hvhv_ppuu_a.ndevice or fn_hvhu_uupp_a.ndeveice would lead better result.
  fn_hvhv_llmm_a.ndevice (LSB-L and LSB-H)
  fn_hvhv_mmll_a.ndevice (LSB-H and LSB-L)
  fn_hvhv_ppuu_a.ndevice (USB-H and USB-L)
  fn_hvhv_uupp_a.ndevice (USB-L and USB-H)
• 4 GHz > (Frequency difference) ≥ 0 GHz:
  You can use any of four sample tables below as long as FOREST can be tuned at the target frequency (ex. ¹²CO line at 115.271 GHz cannot be observed, when you intend to use LSB-L and LSB-H. This is because LO frequency range is limited to 86-116 GHz).
  fn_hvhv_llll_a.ndevice (LSB-L)
  fn_hvhv_mmmm_a.ndevice (LSB-H)
  fn_hvhv_pppp_a.ndevice (USB-H)
  fn_hvhv_uuuu_a.ndevice (USB-L)

FOREST 1-Beam (Single-Beam) mode

The sample device file listed below is for observations with FOREST Beam 1 only. Note that a simultaneous observation using IFs of USB-L and LSB-H is forbidden (i.e., f1_mmuu.ndevice is not available), and number of arrays must be less than 8. Both limitations are due to the mechanical reason.

FOREST 2-Beam (On-On scan) mode

The following table is designed for On-On observations with Beam 1 and Beam 3 of FOREST receiver. As FOREST with Single-Beam mode, you cannot use IFs of USB-L and LSB-H, simultaneously. Array 01, 02, 03, 04, 09, 10, 11, and 12 are for Beam 1, while Beam 3 is connected to array 05, 06, 07, 08, 13, 14, 15, and 16 (also see the figure below).

FOREST 4-Beam Normal (non-SpW) mode

The following tables are designed for the normal 4-beam observations with the FOREST receiver. You cannot use IFs of USB-L and LSB-H, simultaneously.

FOREST 4-Beam Spectral Window (SpW) mode

The sample device files for FOREST with the spectral window mode are listed as follows:

Special Notes for Spectral Window Mode of SAM45 with FOREST

• All beams and polarisations of the FOREST should be the same frequency setting.
  • Users should decide ONE(1) frequency for the 1st LO.
• Two(2) groups of IF chains are available: IF-A (IF01 – 08) and IF-B (IF09 – 16).
• Each group (IF-A/IF-B) contains IF outputs from all beams and polarisations, 1-H, 1-V, 2-H, 2-V, 3-H, 3-V, 4-H, and 4-V.
• Users should decide which IF-Sideband (USB-L/USB-H/LSB-L/LSB-H) assigns to IF-A and IF-B, respectively.
• In IF-A (=SAM45 Sub-Array 1):
  • Users can set two(2) spectral windows within a 2 – 4 GHz.: spw1, spw2.
  • These are independent from IF-B (=SAM45 Sub-Array 2)
• In IF-B (=SAM45 Sub-Array 2):
  • Users can set two(2) spectral windows within a 2 – 4 GHz.: spw1, spw2.
  • These are independent from IF-A (=SAM45 Sub-Array 1)
• Each spectral window:
  • The number of channels of output spectrum is fixed to 2048.
  • Users can set channel separation (or bandwidth) and position for each spectral window.

• Figure 3 shows a schematic view of frequency conversions/setups from FOREST to SAM45 (Spectral Window mode)
• These setups are very complicated.
• Please refer example setups below, initially.
• If you have any questions, please contact us via Helpdesk

Example Setups

Example 1) ¹²CO(J=1-0), ¹³CO(J=1-0), C¹⁸O(J=1-0)

Example 2)¹³CO(J=1-0), C¹⁸O(J=1-0), SO, CS(2-1)

Example 3)¹³CO(J=1-0), C¹⁸O(J=1-0), SO₂, N₂H⁺