Diff for "TelescopeSystemSummary"

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• This page summarizes the present instrumentation at the 30m observatory. The current status is described on another [http://www.iram.es/IRAMES/mainWiki/TelescopeSystemStatus page].

TableOfContents(4)

Frontends

Heterodyne Receivers

A,B,C,D single pixel receivers

A maximum of four receivers, from the total of eight, can be used simultaneously. The following table summarizes the allowed combinations and some of the most important receiver characteristics. Plots of the receiver characteristics.

HERA 3x3 dual-polarisation 1.2mm array

HERA cannot be combined with other receivers; up to now not all frequencies have been pretuned. Hera has 18 pixels separated by 24". Local contact for HERA: Albrecht Sievers

||C150 || || || || || || || || || || || || || || ||D150 || || || || || || || || || || || || || || ||A230 || || || || || || || || || || || || || || ||B230 || || || || || || || || || || || || || || ||C270 || || || || || || || || || || || || || || ||D270 || || || || || || || || || || || || || || ||HERA || || || || || || || || || || || || || || ||HERA || || || || || || || || || || || || || ||

1. Using a special external LO, frequencies down to 77 GHz can be measured with good sideband rejection. For frequencies below 77 GHz, the sideband recection becomes weaker, and the sideband ratio reaches unity at 72 GHz
2. Noise increasing with frequency
3. 2x(3x3) pixel receiver with a 24" separation of the pixels. Equipped with a derotator allowing to follow a source in the sky maintaining the same "footprint".

Bolometers

Table

local contact for bolometers: Stephane Leon

Efficiencies and Half-power beam width

Below you find the most recent values for the forward and beam efficiencies. We have also compiled the value of the efficiencies in the past .

Here you can find the plot with the most recently measured beam efficiencies.

Table

1) The HPBW can be well fit by: HPBW() = 2460/freq(GHz).

2) The data can be well fit by a Ruze function B_eff = 1.2 epsilon exp[-(4pi R sigma/ lambda)^2] with sigma being the rms value of the telescope optics deformations, R the reduction factor for a steep main reflector, epsilon the aperture efficieny of the perfect telescope and lambda the wavelength in mm. The data can be fit by R*sigma = 0.07 and epsilon = 0.69. The aperture efficiency of the 30-m telescope can be obtained using eta_a=B_eff*0.79

3) For a Gaussian source and beam size, and a source which is much smaller than the beam, S(Jy)/T_mb(K)=8.18E-7*theta(")^2*nu(GHz)2 (Rohlfs & Wilson, Tools of Radioastronomy (2. ed., Eq. 8.20). Using the approximation in 1) yields for the 30-m telescope S/T_mb=4.95 Jy/K. S/T_A* is obtained by multiplying 4.95 J/K with F_eff/B_eff

Table

4) The values for F_eff are valid after the 12th of December 2000 when a new reflecting ring was put around the secondary mirror. The moon efficiencies are equal to forward efficiencies (Kramer et al. 1997).

Backends

Spectrometers

Table

Bolometer backends

Spectral Line Observing Modes

• Position switching: only relative OFF positions possible (radio projection offsets).

• Wobbling secondary: max. 240" throw at 0.25 Hz, standard phase duration 0.5 Hz.

• Frequency switching: max. 45 km/s throw at max. 0.5 Hz., with 100 kHz filters and autocorrelator only

• On the fly mapping: Works with all receiver and backends, typical dump rate 0.5-1 Hz

• Polarimetry: using VESPA as an IF polarimeter

• Pointing: Using nearby (within 10 degree) pointing sources, <1" accuracy can be obtained; with absolute ("blind") pointing, the accuracy is <4", the receivers are usually aligned within 2". Checking the pointing and alignment (using e.g. a planet) is the responsibility of the observer.

• Focus: residual errors of <1mm may need correction. There may be systematic differences (<0.4") in the focus of the different receivers. Check focus at least at after sunrise and sunset.