Beacon satellites and KAIRA

150 MHz beacon satellite COSMOS 2454 drifting through a stationary beam pointed at direction of closest approach. 

As we are slowly starting to get the system up and running, we are doing various passive measurements to ensure that the system is in fact working as we would expect it to. One of the passive tests that we are doing is measurements of beacon satellites that fly over KAIRA. More specifically, we are using beacon satellites that transmit 150/400 MHz frequency pairs. We are using these types of satellites already for recording relative electron density curves in another project. With KAIRA we can of course only listen to the 150 MHz band, but this already gives us a nice way of observing our beam patterns. Here is result of the first such test, for a COSMOS 2454 that passed over with a peak elevation of 87.3 degrees. We used one beam to observe at the direction of the closest approach and recorded the signal power within a 200 kHz band. As expected, as the satellite passes the beam, we see the power fluctuating as it goes through the main and side lobes of our receiver beam. In the upcoming days we will be doing more such tests, comparing carefully the location of the satellite with the received signal power.

While the Astron group did a lot of tests that could be considered first light, this is the first light measurement with KAIRA for me.

The LBA cable mausoleum

As we've seen recently, we've been adapting cables to get the suitable lengths. However, these lengths are still fixed, and the antennas themselves are are quasi random distances. Thus, there is additional cable to "bury". On conventional LOFAR stations, this is done by physically burying them... hence the term "cable grave". On the KAIRA site, due to the freezing ground and other environmental complications, we have ours encased above ground in a so-called "mausoleum".

Today, as promised, we have some photographs of the fitting of the cables in the LBA mausoleum.

The LBA cable mausoleum. Seen strewn about are some cables that are only partly deployed. To allow us to stop things from getting mixed up and tangled, they are drawn out along the site until they are ready to be inserted into the ducts. (Photo: D. McKay-Bukowski)

The "U-boat hatch". This pipe goes down into the ground to where the entrances to the long main cable ducts are. This is a very cramped space and is quite difficult to work in. (Photo: D. McKay-Bukowski)

Paying out the draw string for the cables. The total duct length is over 50m and pulling the lines through this length can be quite challenging. Even after we opened the intermediate draw pits the force required on the lines is still quite high. (Photo: D. McKay-Bukowski)

Surplus cable in the mausoluem itself. We took immense care to ensure that no looping occurred in the cables as they are folded into the space. (Photo: D. McKay-Bukowski)

A new view from Saana

A few days back, some of the team went for a hike up Saana Mountain. From near the summit, it is possible to get a good view of the KAIRA site.

The view of KAIRA from Saana. (Photo: A. Jutila)

The grey at the top of the image is actually the water of Siilasjärvi. The buildings to the front left are the Customs Station on the Fenno-Norwegian border. (The actual border is to the right of this image; KAIRA is definitely still in Finnish territory!) At the time this photograph was taken, we were mid-way through the build of the LBA array.

Cutting new cables

In yesterday's post, we went through the reasons why we need particular lengths and how we were going to optimise the cable deployment. Today, we have some photographs. These show some of the steps involved in adapting our existing cable set to the altered site conditions.

The "workshop". This is one of the site shipping containers, temporarily fitted out to provide a cable assembly area. (Photo: D. McKay-Bukowski)

Fitting new connectors to the end of a cut cable. (Photo: D. McKay-Bukowski)

Tools of the trade. Various cutting tools, connectors, and the portable cable analyser units. These are used to measure the propagation delay of the newly completed cables. (Photo: D. McKay-Bukowski)

And, finally, here are some cut and prepared 40m cables, ready for deployment on the KAIRA LBA field. (Photo: D. McKay-Bukowski)

The cable plan

When we designed the LBA array, the original plan was to locate it on the tundra field to the northeast of the HBA array. As we have reported before, this proved to be impossible, due to problems with the soil, snow and prevailing conditions. These things happen in science, but the important thing is that the project can adapt to setbacks and adjust accordingly so that alternatives and workarounds can be found. In the case of the KAIRA LBA array, we have instead deployed the aerials in the solid area to the southeast of the HBA array. In terms of ground stability, this area is perfect. However, it does present a challenge in that extra length is required on the connecting cables.

To overcome this, we are making use of the existing cable set that we have. Firstly, we carefully planned the system of ducts and nodes, and then determined what cable lengths could be expected.

Diagram of the LBA field, with cable runs marked. The shading indicates the length of the cable required to a given location. The lighter the shading, the longer the cable length. The lengths are all calculated by the routing/planning software that we have written, thus allowing us to optimise the use of the existing cables, and thus minimise waste and keep down cost.

Then, the installation order and placement was determined. We compared this to our cable inventory, of the parts that we actually have and worked out that we could complete the array with the following lengths:

     2 × 80m pairs
     20 × 115m pairs
     24 × 120m pairs
     2 × 130m pairs

In fact, the 120 and 130m lengths were made by joining cables together. The 130m lengths were made by joining existing 80m and 50m cables from our inventory together. The 120m cables were made by joining existing 80m cables with 40m cables. There is no standard 40m cable length, so the ones we used were made by cutting a 80m cable in half.

As you can probably tell, we have lots of 80m cable lengths in our inventory.

The reason why the cables come in set lengths is for ease and cheapness of manufacture. The tolerances on the cable lengths that we use are quite strict, so we need to control this process quite carefully. Additionally, it is important that the propagation delay (how long it takes the signal to travel down the cable) is known very accurately... ideally to a fraction of a nanosecond. You make remember from our "how it works" series, that the pointing direction of the instrument is controlled by controlling the signal path delays. So, to be able to do this well, you need to know the existing delays in all the cables before adding any more.

This work has now been done and we are putting together the calibration tables now. I will post some photographs for the cable work, along with some others from the LBA build tomorrow.

Drawing the line

The LBA-cable-mausoleum (also known as the "Postila mausoleum") is getting pretty full these days. With more and more aerials being installed, it is difficult to manoeuvre in and the cables are getting increasingly hard to pull through. Here are some photographs from this process.

Firstly, it is important to recall that the cables are installed "backwards". Although the signals go from the aerials to the RF-container, the cables are physically installed the other way. Each pair (X and Y polarisation cables for each antenna) are inserted into the ducts and are drawn through the long pipes to the common point at the edge of the LBA field. This is where the LBA-cable-mausoleum is located.

Here, there is a large piece of vertical agricultural drain, large enough to fit a person in, and certainly big enough for a lot of cables. We refer to it as the "U-boat hatch", as that's about the size of it and it occasionally floods with water. (Incidentally, the flooding problem has now been fixed as we've added a new drain to the side to get the water out.) We wrote about the installation of this hatch earlier (LINK).

In the finished state, the cables will go into the mausoleum itself to "burn off" excess length due to the non-uniformity of the array. However, during the installation they are first installed directly into the white ducts that go from the mausoleum to the nodes. There are a number of different cable nodes on the field, each server a few aerials. Each node has its own narrow duct, and the cables need to be fed into the correct duct and drawn through to the node itself.

Feeding the cables in to the white duct pipes. The thin white lines are the draw strings. (Photo: D. McKay-Bukowski)

The cables are pulled through to the nodes where they branch off to the individual aerials according to the trenching plan.

Pulling the cables through to the node. From there, they go in pairs to individual antennas. (Photo: D. McKay-Bukowski)

Once a cable pair has been pulled through into the node, it can be pushed through the remaining duct to the actual aerial location. Once both the aerial end, and the RF-container end, are secured, the excess cable is pulled through to the mausoleum in the centre and is zig-zagged back and forth to tack up the slack.

The cables are then scanned, as we keep an inventory of which cable was installed where. This is important as we need to know the exact lengths and propagation delays used in each location.

Thus, the cable installation for that antenna is completed.

LBA installation progress — 27-Jul-2012

We've done it! At last the final LOFAR LBA aerials have been erected on the field. All 48 are now in place and the field is looking pretty complete. We still need to sort out some cabling in the LBA-mausoleum, and this will be carried out soon. However, for now, we can pause and celebrate the accomplishment of getting the aerials in place. Here's the final progress map:

Over the course of the next few days, we'll be posting up loads of photographs from the LBA build work, as well as reporting on the next stage of the installation and commissioning work. We will also be working on the data processing and some inventory work over the weekend. But, for now...

... have a nice weekend!