A History of the Mopra

SIS Receiver

A History of the f****** Mopra SIS Receiver

What is this SIS receiver thingy?

A radio-telescope receiver used on the ATNF’s Mopra dish.

A dual polarisation receiver capable of observing in the 84 GHz to 116 GHz frequency range

The translation of the astronomical signals at high frequency to a lower frequency is achieved using Superconductor-Insulator-Superconductor (SIS) mixers cooled to 3.5 K

It looks like this…Outside… …Inside

It had a grid polariser that had to be protected at all costs…

…and no spare mixers!

Way back when….There were always thoughts of millimetre observing on an ATNF telescope.

Mopra’s wheel on track configuration was thought to have the potential for better support of the dish surface compared to the Narrabri configuration and this idea was floating around in the mid 80’s Compact Array design period.

The Mopra dish surface used to have solid surface to a diameter of ~15 metres

1990- Papers encouraging the development of millimetre capabilities within the ATNF

- Peter Hall a notable proponent via internal reports. No shortage of enthusiasm from John Whiteoak

- Graham Moorey at NRAO’s Kitt Peak mm wave telescope gaining experience

- SIS is state of the art

1990-92- Moorey sets up a lab to make the SIS receiver.

- Carrad goes to work for NRAO in Tucson

- NRAO’s John Payne in Oz and does design work

1994- ‘Proof of concept’ receiver is installed.

- Tuning must be done at the receiver using individual electronic boxes rather than the integrated electronics that was to come.

- Only one polarisation available

First light!

1995- A more integrated receiver is installed.

- Tuning must be still be done at the receiver but all electronics is now ‘on board’ to eventually allow remote tuning.

- Two polarisations available

The paddle wasn’t always thereAn early scheme had a rotating chopper with absorber to give ‘dynamic’ Y-factors referenced to the sky but it’s inception was foiled by the desire to incorporate it into the rest of the standard AT synchronous demodulation scheme. The time constants involved rendered it less than useful and the paddle was used in its place.

1997 Computer control of tuning from a control room PC made available (Simon Hoyle)

Additional control and monitor electronics were installed to allow this.

Surface adjustments

A coma lobe is revealed

Subreflector or optics box or alignment?

Beam patterns measured from the optics box and modelling suggests that the optics box/receiver combination is not the cause

A subreflector shift improves the situation

‘On-telescope’ tests suggests the receiver and optics box.

2000UNSW collaboration with ATNF leads to the dish

receiving a solid surface out to 22 metres

Receiver performance coincidentally tied to frequency

Receiver noise temperatures were of the order of 80K in the 80 GHz region rising to

~120K in the 115 GHz region

UNSW ‘Friend of Mopra’A scheme whereby a UNSW person was dedicated to learning how to use the system and assist other users

The ATNF also assigned a Mopra ‘helper’.

Stuart Robertson, Juergen Ott

Ramesh Balasubramanyam, Lucyna Kedziora-Chudczer, Cormac Purcell.

Combined with the Induction days the scheme was a welcome innovation

Long serving assistants

Robina Otrupcek

Mike Kesteven

Warwick Wilson and his group

A host of Narrabri staff

Graham Moorey

Evolution of the Optics box

The optics box was required because the feed was cooled and hence located inside the dewar.

The constraints imposed by the structure and the position of other receivers made it unfeasible to position the feed at the Cassegrain focus so the beam was expanded and refocussed.

Optics Box Version 1

1994-1998

Its size restricted the range of turret rotation

Optics Box Version 2

1998-1999

This change allowed the turret to be rotated through its full range

Optics Box Version 3

2000-2005

This version achieved full illumination of the dish surface

Version 1 Version 2 Version 3

Outcomes of its use

Data for many projects and notably PhD data for students like Kate Brooks, Maria Hunt and Eric Muller.

A useful test bed for other systems on the ATNF’s Compact Array both engineering wise and astronomically.

An educational tool and filter for UNSW students. Only the strong will survive

The scroll compressor was a test bed for the upgrade to the Compact Array and the model for ALMA

A Testimonial from John Whiteoak

“I realise that a lot of people have criticised the final product, but I was not one of them because I enjoyed using it. I believe it provided state-of-the- art performance and if it was a bit of a bugger to adjust then so be it. The systems on SEST were equally difficult when I first used them in the later

80s, and this continued until they were replaced by newer systems, such as is now being done at

Mopra.”

Sept 2005 Old replaced

by new

True to form…

…a mm receiver brings the rain

Thanks

• John Whiteoak• Mal Sinclair• Graham Moorey

Questions??