KAIRA jänis attack
|Mountain leveret under the High-Band Antenna array (Photo: J. Keskitalo)|
But don't be fooled
They are trained antenna killers!
For some reason, like like to gnaw on cables. And the elastic guy lines of the KAIRA Low-Band Antenna (LBA) array aerials are a particular favourite. On the old KAIRA construction web log, I had often reported KAIRA jänis attacks. Things have been quiet lately.
However, in the last few days, we've noted the loss of signal from LBA antenna #L38. Puzzled, we've investigated to find out that at 18:42:40 UTC on 17-Oct-2017, there was a sudden loss of signal on receiver unit (RCU) #077 (which is the Y-polarisation of LBA #L38).
Some time later, there was a loss on RCU #076, which is the X-polarisation of the same antenna. This happened somewhat gradually over the course of approximately 1 hour, starting roughly at 07:50 UTC the next morning.
The loss of the X-polarisation was somewhat gradual. It was accompanied by a deflection of the Y-polarisation too. Here are both traces, at around the time of the loss of the X-polarisation.
Zooming in on the time range, it seems that the initial fall of the Y-polarisation happened quickly, within the space of a couple of seconds. Here is the sequence of the spectra as the fall occurred.
It is difficult to say exactly what happened, but my hypothesis is that the jänis chewed the elastic through at 18:42:40 UTC on 17-Oct-2017, causing the Y-polarisation to "short-out". The post remained upright and the X-polarisation continued operating. Then the next morning, the antenna slowly listed over and fell, possibly under the weight of the snow. Further snow has then covered it, rendering the antenna completely inoperative.
Well, this will need to be fixed.
The location is as follows (click to enlarge the plot, but the recent loss is the grey square near the bottom of the LBA array - otherwise marked in green on the status map, as we are currently observing in RCU mode 3).
Meanwhile, KAIRA continues operation with 47 antennas.