We discussed in this post how we wired up the entire signal chain to the 2.5m dish at the University of Exeter and took our first observation. In this plot we could make out the several features of the Milky Way galaxy traced out in HI emission. This post was cheekily titled “First Light… Kind Of” referencing the fact that all of the crucial electrical components of the telescope were indeed wired up and doing the actual observation, but it wasn’t using our finished dish. Well, I’m proud to announce that this is no longer the case, as after over 4 years of planning and construction by our dedicated team, XRT-C has achieved first light.

The actual observation came at the end of a long build day on the 13th May 2017. The first job was to correct wiring faults within the cables run between the control room and the motor drive. Because the original cabling was bought before we found our home at Caradon Observatory, it was considerably shorter than we required. Longer extension cable was purchased and connectors were affixed to allow it them to be connected to the existing wiring. However, due to a a number of issues with the fixings on the end of the wiring, we were never able to get a consistent connection and actually slew the dish from the control room. The first job of the day was to do away with this flawed wiring and directly solder together the wires. This method makes the setup less flexible, but much more reliable. After this was completed, we were finally able to freely slew the telescope from the control room.

Undergraduates Alexis and Marine carefully rewiring the cables to the motor drive.

The next thing that needed to be taken care of is finally mounting the struts onto the dish. These struts are required to hold the feed horn at the prime focus of the telescope; the place where the incoming radiation is focused to by the parabolic shape of the dish. There are four struts in total, positioned at 90° intervals around the dish. They can be mounted anywhere on the dish as long as they are on a strut, but we opted to mount them at 45° from horizontal  and vertical. This more evenly spreads the weight of the assembly across the struts, and the dish. After some careful maneuvering, three of the struts were in place and the feed horn was mounted.

Dimitar preparing to fix the low-noise amplifier, now wired to the power and signal cables, to the feed horn.

After the final strut was positioned and fixed, the dish was finally structurally complete, all that was left to do was wire it. We ran power cable and the low-loss coax up one of the struts and into the low-noise amplifier attached to the side of feed horn. When this was all secured we retreated to the control room for a well deserved break. Now it was time for the big event. We were about to make our first observation with the telescope. We went to make an observation only to find that the fuse in the Rot2ProG, the controller for the motor drive, had blown its fuse, so we were unable to move the telescope away from pointing toward the horizon. Unperturbed, we decided to make an observation regardless and we were greeted with no signal. After a couple hours worth of persistent head scratching, we finally observed this…

The first observation of the completed setup. Unfortunately, due to a technical issue with the motor drive we weren’t able to slew to an interesting part of the sky, but this is the first 21cm emission from the completed telescope and electronics.

It was pointing towards a hill, but this is still the very first observation made with our completed, mostly-working telescope. You can see this plot zoomed in further up the page. Needless to say, we have more fuses on order, so we’ll be trying to observe something in space very, very soon.

What’s Next?

This is a very exciting time for the project. We now have a working telescope and great collaboration going with Caradon Observatory. It is now time to start commissioning. We need to work out a flux calibration for the telescope, so that we can convert volts to a physically meaningful unit, we need to calibrate the pointing of the dish so that we know what we are observing and when all of this is done we can actually start observing with it. One of our projects involves doing a survey of the galactic plane of the Milky Way in order to weigh the galaxy. We really hope you’ll come along for the ride. You can follow along with us on @xrtcaradon or like our Facebook page.

The completed XRT-C dish at the end of a long build day.