The remains

Following the great Kilpisjärvi Storm of 2014, the telescope rescue crew scoured the surrounding landscape trying to find and recover debris. Part of this was recovering as much scattered electronics as possible... some of which may be able to be cleaned up and re-used as spares.

This sad crate of fragments are some of the parts salvaged during that operation. (Click on the photograph to enlarge.)

Salvaged parts from the destroyed LOFAR HBA tile at KAIRA. (Photo: L. Roininen)

RF patch cables and RCUs

Just a neat photograph today... this one was taken on the day of the official opening, looking across the patch cables going into the Receiver Unit (RCU) subracks.

RCUs and patch cables at KAIRA (Photo: J. Keskitalo)

The astute LOFAR observer will know that this is either an RCU mode 3 or mode 4 observation. (Because the led above all the middle input connectors is lit.) Indeed, we observed mode 3 riometry throughout that particular day.

Cable joins

Inside the mausoleum, we found that there had been considerable snow build-up. This may be a contributing factor to the failed join (and that was precisely what it turned out to be). Here are some photographs of the situation as we found it and the problem cable.

Snow of the cables in the mausoleum. (Photo: D. McKay-Bukowski)

The culprit. A loose ground connection, possibly caused by a misseated o-ring. (Photo: D. McKay-Bukowski)

LBA mausoleum sealed

With winter approaching, and the LBA cabling problem sorted out, we've sealed up the mausoleum ready for winter.

The LBA cable mausoluem, with a bit of frost on the roof. (Photo: D. McKay-Bukowski)

Fixing cable shielding problems

Last week we reported on the work that we were doing on the LBA array bandpasses. We had noted a few problems and have been looking into the cause of them. It turns out that some of the cables with joins did not have a correct ground shielding. The break in the shield occurs at this join location and is caused by resin from the water-proofing forming an insulator gap in the connector threads.

To fix the problem, we need to very careful remove the housing and clean out the resin. The cable connectors can then be re-fitted and tested.

A cleaned and reconnected LBA cable join.

Carrying out this work is extremely time-consuming. Each cable join is taking between 15-30 minutes to clean out and test. Still, it is important work, and it is essential in order to get the entire LBA operational.

The completed mausolea

The cable mausoleum is used to store excess lengths of the cable from the array. There is one for each of the low-band and high-band arrays. Normally this cable is buried (in what is called a cable 'grave'). However, for KAIRA this needs to be above ground (hence the corresponding term 'mausoleum'). Today we have some photographs by Arttu Jutila of the two completed cable mausolea.

The completed LBA cable mausoleum. (Photo: A. Jutila)

The HBA cable mausoleum, in front of the RF-container. (Photo: A. Jutila)

The LBA cable mausoleum

As you will have seen over the last month or so, the excess cable lengths from the low-band antenna (LBA) array are zig-zagged (not looped!) back and forth in a second mausoleum. Well, this part of the project has now been finished off... and here are some photographs from Arttu Jutila of the work.

All cable work complete and the temporary roof removed ready for the finishing work. (Photo: A. Jutila)

Another view. The frames are converted HBA tile frames, of course. (Photo: A. Jutila)

The next step is to add the purlins. (Photo: A. Jutila)

And then the roof itself is added. (Photo: A. Jutila)

Cable work in the RF-container

We now have installed all the patch cables in the RF-container. These are the 6-metre cables that go from the back of the patch-panel under the false floor and into the signal processing racks.

Under-floor cabling. (Photo. D. McKay-Bukowski)

Close-up of the back of the patch panel. (Photo: D. McKay-Bukowski)

Patch panel

In the RF-container, there is the patch panel which has the field cable connected in on the outside and on the inside, there are the patch cables going into the receiver units in the equipment racks. Now that the LBA cabling is finished, we've completed this outside patch work. However, still more cabling remains to be done (sorry!). These photographs show the current situation:

The patch panel, as seen from the outside. (Photo: D. McKay-Bukowski)

The inside of the patch panel, showing the F-type connectors. There is one pair per antenna. The orange connectors are the X-polarisation and the black are for the Y-polarisation. (Photo: D. McKay-Bukowski)

A look at the patch panel. The lower section has the completed HBA patching. There is then a single pair left as a spare and, starting with #47, there is the first of the LBA patch cables. These will be filled in over the next few days. (Photo: D. McKay-Bukowski)

Aerial to node

Going the other way, the 40m cables are run from the aerial back to the node and then from there to the mausoleum. This is because the new metal armours are two large to easily get through the thin antenna ducts.

Fitting the draw clip to the cable pair. (Photo: D. McKay-Bukowski)

Drawing the cables through to the node. (Photo: D. McKay-Bukowski)

By now the cables have nearly reached the mausoleum (left far distance). Note the metal armour near the left. This was fed on from the leading end and will eventually end up at the base of the post. (Photo: D. McKay-Bukowski)

Cables, cables, cables...

Today we have some more photographs from the cable work.

Protecting the cable ends. Because the fitting process takes several days, the exposed cable ends are covered to protect them from the elements. The pegs keep them up off the ground and stop water from running into them. (Photo: D. McKay-Bukowski)

Although one end is out across the site, the other end goes into the mausoleum. (Photo: D. McKay-Bukowski)

Just another photo of cables. (Photo: D. McKay-Bukowski)

Adapting the posts

As we saw yesterday, we have fitted additional armour to some of the cables. The only small setback is that the added diameter means that we need to adapt the base of the LBA aerial posts. Fortunately, this is easily done and there are not many to do.

An adapted cable post. (Photo: D. McKay-Bukowski)

Incidentally, it may seem a bit odd that we are going into such painstakingly fine detail in this weblog.Surely we just want the glorious photographs of the finished product and the amazing data that it will produce. Well, this is certainly true. But this weblog also serves other purposes as well. It acts as a complete record of the work that we've done on the site. It also explains to our readers at ASTRON and EISCAT what modifications we needed to make to the standard LOFAR system to adapt it to the local Arctic conditions. And it is also a step-by-step guide for our colleagues on projects like POLFAR and I-LOFAR, helping them to understand the steps involved, how they are sequenced and what little challenges we meet along the way.

So, yeah, sure... cutting a slightly larger slot in the LBA post may seem a bit trivial, but there is a really good reason for writing about it and posting it for public view.

Cable armour

Because we were cutting existing cables, it means that half of them will be without metal armour. The armour is a short sleeve of metal that goes around the cable. In the final installation, it is located at the bottom of the LBA aerial posts, where the cable comes out the base of the post and goes into the ground. Obviously, the cable is briefly exposed at this point, and the armour prevents animals from chewing on the cable or any other form of damage from being exposed. For the extra armour, we cut short lengths of metal hose and fitted it where necessary.

A collection of prepared metal armour. (Photo: D. McKay-Bukowski)

Fitting the armour is easy. The choice of diameter is such that it easily slips over the female F-type connector on the cable. It is then slid all the way to the other end, near the male connector, which is where it is required. (Photo: D. McKay-Bukowski)

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)

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.

New reel

In the entrance to the RF-container, there are the ends of the cable ducts, where the signal cables emerge from the ground and go into the patch panel. Although the signal path is from outside to in, we actually feed the cables the other way when installing them. As the ducts are getting more and more crowded, we have had to improvise with the installation equipment that we use to do the work.

In this particular case, this meant designing and building a new cable reel. The cables are place on the reel side-by-side (cables for the X and Y polarisations). Although this may not seem like much, it makes a big difference to the work that we do.

The new cable reel, made from scraps of timber, left-over cardboard
and offcuts of agricultural drain. In the background, you can see the
duct entry points and part of the patch panels. (Photo: D. McKay-Bukowski)

Working under cover

There are several long cable runs that need to be made during the installation of the LBA field. These require a moderately dry environment to prevent excess water ingress into the cables. Additionally, we need to protect the trenches somewhat, just to stop them becoming muddy and difficult to work in. As a result, the team decided to build some temporary work shelters over the most vulnerable sections. These are the two mid-line draw trenches and the LBA-cable-mausoleum.

The shelters are not particularly sophisticated. Simply some spare build timber and some canvas. However, the accomplish the task of providing some basic protection for the open draw pits.

Building a frame of the first draw pit. (Photo: D. McKay-Bukowski)

The frame was screwed together to hold it in place. In order to keep the canvas in place, additional support timbers were tied to the frame (square lashings, for any knot-enthusiasts out there!). Then the canvases were dragged over.

Adding the canvas to the first draw pit. (Photo: D. McKay-Bukowski)

In order to secure the canvas to the ground, we used spare LBA anchor pegs. We have enough spare of these to get this done and the pegs have some very handy lugs that allow us to secure the corners of the canvas (with either bowlines or clove-hitches and 2 half-hitches, depending on the location). Not only did the draw pits get covered, but we also put some covering over the cable entry points in the LBA-cable-mausoleum. This was actually a lot easier, as the frame was already in place.

Securing some scrap plastic sheeting to the mausoleum frame. (Photo: D. McKay-Bukowski)

With all this done, we can proceed in pretty much all conditions with the cabling work.

Running the cable pipes

In each of the shallow trenches on the LBA field, there are white agricultural drains, which we use as ducting for the cables. Because we have rocky, unforgiving soil, and the fact that it freezes up each winter, means that we need to provide additional protection for the cables that we have. This is in contrast to other LOFAR stations, where the cables are buried directly into the ground.

Laying the last of the ducts on the field. (Photo: D. McKay-Bukowski)

Taking a break. Yes, the duct has other uses. (Photo: D. McKay-Bukowski)

Installing the ducts leading into the HBA cable
mausoleum. As the ducts get closer to the RF-container, there are
more and more cables in each. This is why the duct diameters
in this location is larger. (Photo: D. McKay-Bukowski)