News from the frontend

Rusty

After 15 years, the frontend in the focal point of the dish of the Dwingeloo Radio Telescope was due for maintenance. Consequently, the telescope would be taken out of operation for two months. The frontend installed in 2008 was reliable and functioned well without major adjustments. The maintenance was planned for earlier, but was postponed due to the covid-19 measures. It was now scheduled for November 2022, and was postponed again to January specifically for the Artemis mission.

Monday, January 9, 2023, the volunteers of the so called “Monday team” began the maintenance work. That was badly needed because various electronics in the focus box had started to rust considerably. All power supplies were brown with rust and the fear was that this could lead to malfunctions.

Components

The parts that would be worked on in current maintenance:

• Focus box frame: the tube construction that is attached to the telescope’s four leg.
• Focus box: a steel box (closed on 5 sides) that can move back and forth in the frame.
• Antenna box holder: also called frontend cart, can be slid over rails into the focus box, contains a steel extension at the front to get closer to the focal point and has wheels to slide out of the focus box for maintenance.
• Antenna box: attached to it are feeds and antennas and it contains preamplifiers, transmitters, power supplies and fans; it is screwed into the antenna box holder.
• Trolley: also called antenna box holder cart, is intended for transporting the antenna box holder with the antenna box and is normally located on the lifting platform, has wheels and can drive back and forth between the radio telescope and the Muller House for maintenance.

(1) Focus box frame on the four-leg, now containing – due to frontend maintenance – the empty and plate-enclosed focus box; (2) on top of the lifting platform, the antenna box holder with antenna box is driven from the focus box into the focus box frame – with Jan van Muijlwijk and Piet Zijlstra; (3) antenna box holder and antenna box on the trolley; (4) the antenna box – removed from styrofoam – in the Jansky lab.

Lifting platform and Jansky lab

It used to take a lot of effort to bring the frontend down for maintenance. This was partly due to the ‘provisional tent’ of green tarp over the pit of the lifting platform – often referred to as a lift – and the lack of a maintenance room. Those obstacles have been removed in recent years: the lift tent has been replaced by a mobile house over the lift pit and the Jansky lab in the Muller House has become a dedicated frontend workspace.

Activities

In summary, operation frontend involved:

• Mechanical maintenance, such as replacing rubbers, removing algae and rust, fixing a fan, a lick of paint.
• Overhaul of the electronics.
• Moving the amateur radio transmitters from the frontend down into the telescope’s control house.
• Resolving the cable connection risk in the focus box.
• Updating the existing documentation of the electronics, the cables/cable connections and the dimensions of the mechanical parts.

The work was carried out by the volunteers of the Monday team (for mechanics, electronics and frontend), formerly led by Cor Veldman, nowadays Brant Visser, supplemented by Jan van Muijlwijk and Jan Kappert from the Tuesday team (for the transmitters and receivers) and other interested volunteers. With extra effort on other days, Piet Zijlstra made the focus box and antenna box mechanically sound and sealed the focus box with a metal plate. Tammo Jan Dijkema and Jan Kappert made extra efforts to update the documentation.

In the last week of March – so, operation frontend was delayed by a month – the work was completed.

Dynamism

After the trolley with its contents was moved down into the Muller House, a real flow of ideas started, including through the Mattermost CAMRAS communication platform. Jan van Muijlwijk commented on this joint process: “Now that everything is down here and many more people are seeing how it all works, ideas are constantly emerging. That is very nice. Sometimes they are ideas that have already been put forward and for good reasons have not been realized. (…) Wonderful, all that dynamic energy!”

When the antenna box was opened, it turned out to house a large fly population. It took them all a long time to disappear from the Muller House … The styrofoam insulation layers naturally provided an ideal breeding ground for insects (see photo above). The foam housing has been completely renewed. Now without glue, easier to remove to get to the antennas, much better sealed and thus better insulated.

Moving the transmitters

Following the cable renewal operation in May 2017, ten coaxial cables lead to the focus box: three 7/8 inch cables and seven thinner Hyperflex13 cables. Previously – with suspicion of possibly kinked coaxial cables – it was irresponsible to send a lot of power through the cables to the transmitters in the focus box. Now that shorter, reliable, thick cables run upwards, it was obvious to move the transmitters down to the control house.

Part of the work therefore consisted of placing the TV transmitter for 70 cm and the other transmitter for 23 cm downstairs in the cabin. The 70-cm has a maximum output of 400 watts. The 23-cm output stage of the amplifier is a much smaller device with a maximum output of 120 watts. Control from the TS2000X transceiver was at 70 cm approximately 12 Watts for maximum output and at 23 cm approximately 3 Watts for maximum output. That will now change slightly because the cables between the TS2000X and the output stages are much shorter.

Solution to the cable problem

A tricky issue when putting the antenna box holder (frontend cart) back into the focus box was always securing it. Previously, all cables in the focus box had to be connected to the antenna box first, after which the frontend cart was driven into the focus box. Because the cables are loose, there was a risk – and that has sometimes happened – of the cables being trapped and damaged.

Na veel brainstormen en na verschillende proefballonnen, is er een oplossing voor dit probleem bedacht: de kabels in de focusbox kunnen op een vast paneel in de focusbox worden vastgemaakt en liggen dus niet meer los. In de plaat voor op de antennebox is een afsluitbaar gat waardoor dit kabelpaneel na het vastmaken van de antenneboxhouder nog bereikt kan worden zodat de kabels van de antennebox alsnog kunnen worden vastgemaakt. Dit briljante idee werd al enige tijd geleden geopperd door Harm Jan Stiepel, geïnspireerd door de Westerbork telescopen. Deze verbetering moet het makkelijker en veiliger maken om het front-end te verwisselen.

(1) Three 7/8 inch cables; (2) seven thinner Hyperflex13 cables; (3) Piet Zijlstra starts installing the cable panel; (4) the cable panel.

In particular, it turned out that the connection of the cabling and the routing could indeed be improved. The photos show how things were and have now changed. Down in the control house, the incoming coaxial and power lines could also be mounted in a neater, more practical and more professional manner.

Finished for now

On Tuesday afternoon, March 28 – after some final struggles – Ed Dusschoten, Jan van Muijlwijk and Piet Zijlstra brought the antenna box up and connected it again. After testing – except for transmitting – everything works as before:

• The pulsar is clearly visible on both horizontal and vertical polarization.
• The 21 cm line is clearly visible.
• At 13 cm (the S-band horn we also used for Artemis) we seem to observe less signal than before. The Sun and also the Korea Pathfinder Lunar Orbiter (KPLO) can be observed quite well, but the signal seems weaker.

We will further investigate the weaker signal, and later other preamplifiers and filters will be installed. However, the major work seems to be finished for now. The Dwingeloo Radio Telescope is back in operation!

Future plans

Operation frontend continues with the development of a second frontend specifically for higher frequencies and a third frontend specifically for radio astronomy.

Because it is now easier to switch between frontends, it is also easier to make extensions to the ‘standard’ frontend that is currently in the focus box. It contains the 23 cm horn, a 13 cm horn (off-focus) and dipoles for 70 cm, all with associated electronics. Extensions include, for example, installing electronics to be able to transmit and receive at a wavelength of 2 m (which would require temporarily attaching the necessary yagi antennas).

But for those future plans, the telescope does not have to be out of operation for three months, as has happened now.