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LA2VHF/4 and LA2SHF QRV from Vassfjellet

Two weeks ago, we wrote about a disheartening trip to Vassfjellet. LA3WUA and LB0VG discovered that almost all the antennas we put up over the course of last year had broken, and that the LA2VHF/4 4 m beacon had blown its final amplifier in the progress. This week we are back with some good news.

After digging around a bit in the final amplifier of LA2VHF/4, it was quickly assessed that all the passive functions were in order. The bias voltage was at 4.6 V, and the supply was nice and steady. The likely culprit was the Mitsubishi power module, so we decided to order a new module from Mini-Kits to replace the broken one.

As word got around that the beacon had broken, we got in touch with ARK old-timer LA9IY, who happened to have one of the modules in his possession. LA9IY agreed to swap his module for the one that we ordered (which has yet to arrive).

To the author’s surprise, everything worked fine after swapping to the new module. Just in case, we left the beacon running on our lab bench for a couple of hours, to see if anything would happen. The output level of the beacon went down by about 1 dB once the beacon started to get toasty, we ended the test when the output level had stabilized. The end result was an output power of approximately 35 W.

On Wednesday the 30th of May, LA1BFA and LA3WUA went up to Vassfjellet to reinstall LA2VHF/4. The 23 cm beacon, LA2SHF, which was built over the course of the winter was also brought along.

Installation was rather painless. For LA2VHF/4 we used the already deployed vertical antenna, which was the antenna in use before we built the (now broken) big wheel antenna. LOS propagation will likely be a bit worse with a vertically polarized antenna, but  for the main mode of propagation – Sporadic E – there should be little to no difference. The reason for this is that propagation through the ionosphere scrambles the polarization, so vertical or horizontal becomes less important.

We installed LA2SHF indoors, using a simple sleeve dipole that we showed how to build in a previous blogpost. On 23 cm, horizontal polarization is desirable as it is more commonly used for the available propagation modes. Examples of such modes are aircraft scatter and tropospheric ducting. For local amateurs it is also nice with better coverage in the line of sight. The reasoning here is that more amateurs have horisontally polarised antennas, so that it is more likely to be heard.

In the spirit of all ARK repair sessions, all did not go perfectly. In our hubris we made a small mistake. LA2SHF is currently operating with the exchange “LA2SHF JP53EK  Beeeeeeep”, this should have been “LA2SHF JP53EG Beeeeeep”. We will make sure to fix this the next time we visit Vassfjellet.

As always, we are interested to hear your reports if you have heard our beacons. You can get in touch with us at la2vhf (at) la1k.no or la2shf (at) la1k.no, or by spotting us on your favorite cluster. Some brief data on the beacons is provided below.


QRG: 70.063 MHz – Power:  ~35 W – Antenna: 1/4 wl vertical – Polarization: Linear (vertical)


QRG: 1296.963 MHz – Power: ~30 W – Antenna: sleeve dipole – Polarization: Linear (horizontal)

Finally, we would like to thank LA9IY for supplying us with a power module, and DL9DAC, OM3CLS, GD3YEO, ON4KST, DH5YM, LA9JK and LB8UG for their signal reports.

Woes of the northern amateur part 2 – Vassfjellet

This Saturday LA3WUA and LB0VG had an outing to Vassfjellet. The goal was to re-establish the radio link, which we have touched upon in a previous post, and investigate how the cabin and equipment had fared over winter.

The former was solved by a little application of the holy trinity – rebooting, resetting and finally re-configuring. The Ubiquity node we use for the radio link had suffered from a mysterious reset, and was somewhat unresponsive in our attempts to restore the original settings. The link is up and running, but the hardware hiccups are worrying. We will look into replacing/fixing this over the summer.

LB0VG, Kristoffer, working on reprogramming the Ubiquity radio link.

As seen in the feature image, the latter did not go particularly well. At Vassfjellet we have recurring problems with ice fall from the huge telecom mast next door. Two years ago we installed a sheet metal roof, which we hoped would stop the ice from piercing large holes in the roof. While the roof is rather battered after this winter, it is still intact.

Unfortunately the same cannot be said for the stack of big wheel antennas that we installed last year.  Harsh winds and ice have brought down all three antennas. The combination of large surface area, which makes a good ice target, and thin/brittle aluminium makes the big wheel uniquely unsuitable for installation at Vassfjellet. Nearly all curved outer parts of the big wheels has suffered fatigue fractures at the points where it attaches to the square booms.

At the time of breakage, both LA2VHF/4 and LA2UHF were connected to big wheel antennas. This poses a serious issue, as both beacons were exposed to infinity SWR for a long time. With infinity SWR, the final amplifier gets power continuously reflected back at itself. If this reflected power is beyond the rating of the final transistor, it could potentially break…

We quickly got LA2UHF back up using the old indoor yagi antenna, but LA2VHF/4 is another story. After confirming that it could not be heard by other amateurs in the area, we decided to dismantle it, and bring it to the lab. As a result LA2VHF/4 is temporarily QRT.

Our suspicions were confirmed in the lab: LA2VHF/4’s final amplifier is blown. Fortunately it seems that only the RA30H0608M power module has taken damage. The voltages around the amplifier board checks out, and there is no indication of damage on any other components. The CW beacon board has also fared well, possibly due to the in-line attenuator (blue device in the first picture below) between it and the power amplifier.

Winter always seems to treat us well, keeping us entertained with exciting maintenance projects to complete over the summer. We have ordered spare parts, and hope to have LA2VHF/4 up and running as soon as they arrive. We will be back with an update once the beacon is back in service.

Preparations for ADS-B reception at Vassfjellet

We’ve been planning to set up a receiver for ADS-B  at Vassfjellet for some time, and after after the upgrade of our 5 GHz link, the time has come to finally do something about it.

Automatic Dependent Surveillance Broadcast (ADS-B) is a service that is required onboard planes above a certain size. We’re already running a receiver at Samfundet (JP53ek) powered by an RTL-SDR and dump1090. This setup is giving us around 180 nautical miles in maximum reception distance (according to fr24 receiver statistics). We’re hoping to improve this by installing another receiver at Vassfjellet, which is at over 700 m above sea level. The setup for Vassfjellet will consist of the following parts:

  • Raspberry Pi
  • 1090 MHz collinear antenna purchased from eBay.
  • 1090 MHz bandpass filter purchased from eBay.

We had the opportunity to go a little overboard with the measurements of the setup: both horizontal and vertical antenna pattern, S-parameters, noise figure and gain were measured. Many thanks to Jens (LB6RH) at the Department of Electronic Systems for helping us measure the antenna in the anechoic chamber at NTNU.

Antenna mounted vertically in chamber.

Radiation pattern of antenna mounted vertically.











The figures above show the mounting position and the measured antenna pattern for the vertical plane. We can see that the antenna performs excellently with an almost omnidirectional pattern.

Antenna mounted horizontally in chamber.

Radiation pattern of antenna mounted horizontally. The diagram is oriented so that 0 degree corresponds to the colinear antenna pointing straight towards the reference antenna.






To assess the take off angle of the colinear antenna we mounted it horizontally and changed the reference antenna to a horizontal configuration. The results and mounting position can be seen above. The large lobes at 80 degree and 270 degree correspond to elevation angles 10 and 0, respectively. This means that the horizon is well illuminated and that we will have good reception for multiple planes. Further we see that the sidelobes are more than 10 dB below the main lobes, ensuring that the antenna has good gain.

Filter insertion loss.

Colinear antenna return loss

The S-parameters for filter and antenna were measured using a miniVNA Tiny and are displayed in the figures above. The performance of the filter and antenna are similar to what their manufacturers claim.

Measurement setup for Noise Figure and Gain measurements.

The next measurement shows the measured noise figure and gain of the LNA4ALL. This was done using the FSV-K30 option on a R&S FSQ signal analyser with a HP 346B noise source, as seen in the figure above.  We will get back to this measurement in a separate blog post.

Measured noise figure (blue) and gain (black) for an LNA4ALL

We are very satisfied with these measurement results, and look forward to seeing how the equipment will perform once installed at Vassfjellet. We hope to be able to receive many planes.

Installing an AIS receiver at Vassfjellet

This weekend we put up a Automatic Identification System (AIS) receiver while making some improvements on our internet link to Vassfjellet.

Improving the link

Last year we installed a 5.8 GHz radio link between Samfundet and Vassfjellet, where we have our radio beacons. The radio link will allow us to remotely check status of the beacons, and allow for several exciting monitoring applications.

We found out that we had done a mistake in choosing the feedline between the Ubiquity rocket M5 and the antenna. The mistake has nagged us over the entire winter, so when the snow on the road finally melted, we bolted up the mountain.

LB0VG terminating RJ45 plugs for the link. LA1BFA inspecting important assets in the background.

The feedline was around 6-7 meters of a RG-58 type. At 5.8 GHz this turns out to have a massive attenuation, approximately 13 dB. By simply replacing with a shorter and better cable, we could get a huge improvement in link quality.

To get as low cable loss as possible we decided to mount the Rocket right behind the antenna. We bought some 15 cm RP-SMA to SMA pigtails that use RG174 cable, which should give a cable loss of only 0.56 dB. The resulting improvement is seen below.

When we took the link down at 12.00 UTC the link margin was 10 dB. We had it up again an hour later, and the link margin is now 22 dB. This is very much in line with the cable loss improvement mentioned above.
This improvement in link margin will be very nice when we start adding more services up there.

Marinetraffic AIS receiver

Boats over a certain size are required to report their position using AIS. This makes for very interesting listening, as you can effectively stalk the movements of large boats.

Marinetraffic is a website where reports from a network of AIS receiving stations are gathered.  Marinetraffic are also interested in unique sites that will allow them to expand their coverage, see their application form here. We got in touch with them, and they were interested enough to send us:

We tuned the antenna to 162 MHz using our AA-170 antenna analyzer, and got it to resonate with about 1.2 VSWR. The antenna was plugged to the SLR350Ni, which surprisingly is based on a Raspberry Pi 3 with a radio daughterboard. After a small power struggle with the software and trying to set it to a static IP, we started receiving ships.

We were a little worried about the receiver getting a lot of interference from LA2VHF, as they are in the same band, and very close. But it looks like everything is working smoothly.

LB0VG handing LA3WUA the Rocket modem. Behind LB0VGs head is the newly installed AIS antenna.

Below is a display of the ships that we have received. On average we get 200 AIS messages a minute from about 100 ships, with a maixmum reception distance of 463 km. I’m confident that by adding some filtering, an LNA and maybe a small yagi antenna, we can get more than double of this.
You can also find live information on our Marinetraffic station page.

AIS messages from boats near the Trondheim coastline. Vassfjellet receiving station in lower right.

It’s very nice to finally get some traffic over the link. Over summer we’re hoping to expand with more monitoring services, but that’s a story for another blogpost.

LA3WUA demonstrating a patented LA1K antenna hoisting method.

SatNOGS station back on track

We recently discovered that our SatNOGS rotor was mounted with a 90 degrees offset, which made our setup a bit tricky to use. Our efforts to do a drop-in replacement of the broken USRP N210 with an RTL-SDR were therefore temporarily blocked.

LA3WUA Øyvind and LB6RH Jens went on to make the appropriate corrections a couple of weeks ago.

Long-legged assistance was needed from LB6RH due to our dear little friend LA3WUA not being able to reach the antenna (note from dear little blog post author: I wouldn’t either).

The rotor controller was set to 180 degrees azimuth, and the rotor appropriately rotated to the physically appropriate rotation direction towards Vassfjellet.

Good work, Jens! And good work to you too, supporting background character/photographer LA3WUA.

Unfortunately, we were not quite finished. Continuing off of the software issues in the last post, we realized we should upgrade to the latest Ubuntu LTS. This gave us a librtlsdr version without the No supported tuner found issues, and everything was looking good for some time.

Before we did that, we also scheduled a couple of observations just to see whether the full software system was working as expected, and discovered that our observations were not really uploaded to the server. This was not that surprising since there had been major releases of the SatNOGS client software since we installed it. The entire installation in any case broke down after the Ubuntu upgrade due to some Python incompatibility issues, so it was a good time for getting up to scratch with the latest versions. LB6RH went to work.

We have no appropriate photos of LB6RH working on the current SatNOGS installation, so here is a photo of LB6RH possibly doing something else.

Turns out that there exists a Debian package repository for the SatNOGS software. Unfortunately, these packages were not as compatible with our Ubuntu installation as we could have wished, due to strict dependencies on e.g. Python3.7-related packages, while Ubuntu 20.04 LTS has only Python3.8 available. After getting started on building from scratch, we sat back, thought for a bit, and realized – why suffer? We should just make the switch to Debian, and mirror the build system of the SatNOGS team.

And so we did (or, well, Jens did). Jens could conveniently use the standard instructions for using Ansible to set up the system, which might be a story for another time, and presto – we had a working SatNOGS system again.

Waterfall, SatNOGS observation 2336545.
Decoded satellite image, SatNOGS observation 2336545.

We are used to rather horrible NOAA reception, which made relatively good signal reception here a pleasant surprise. Whether this is due to our old USRP N210 being exceptionally crappy towards the end, or due to exceptionally low noise conditions during the summer months, we don’t know yet, but it will be exciting to see in the long run.

We are still not quite finished since our rotor controller is acting up and sporadically timing out again, so we are making do with fixed antenna positioning for the time being until we can figure out what is wrong with the controller.

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