Akademisk Radioklubb

LA1K / LA1ARK / LA1UKA

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
  • RTL-SDR
  • 1090 MHz collinear antenna purchased from eBay.
  • 1090 MHz bandpass filter purchased from eBay.
  • LNA4ALL

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.

New beacon antennas for LA2VHF (4m) and LA2UHF (70cm)

For a while now, the beacons on 4m and 70cm have had sub-optimal antenna systems.  We decided to install new Big-Wheel antennas for both bands, as an experiment.    The “Big Wheel” is a horizontally polarized omni-directional antenna.

Getting ready

Getting ready for departure. A 6 meter long steel mast, 3 Big Wheel antennas, and 4 hams

The installation was performed in typical Norwegian summer weather – rain and wind.

Antenna assembly

Øyvind (LA3WUA) and Arne (LB7JG) assembling a Big Wheel

In addition to the 70 cm and 4 m Big Wheel antennas, we put up a 6 m version as well.  We don’t currently have a beacon license for 50 MHz, but since there has been allocated a new beacon segment above 50.400 MHz, there might be room for us there.  Stay tuned – perhaps LA2VHF will show up on 50.463 some day.

Final adjustment on the 6m Big Wheel. Arne (LB7JG) and Øystein (LB7IG) in intense competition – manual or electric?

6 m and 70 cm big wheels were bought from Wimo. The 70 cm version is a very neat design that comes pre-assembled. Some assembly is required for the 6 m version.  We had a lot of trouble getting the aluminum tubes to fit inside the square aluminum pieces. In the end we had to file the tips so that they would fit. If you are planning to build this antenna, make sure to have some lubricant and proper tools at hand.

For 4 m there are no commercial designs. Our solution is a custom design based on the build notes OE5MPL and OE5VRL provide on 70MHz.org.

70 cm and 4 m Big Wheel is mounted. Now, the 6 m remains. Øystein (LB7IG) and Sveinung (LB1SH) receives the antenna from Arne (LB7JG)

If you hear any of the beacons we would love to hear about it at LA2VHF or LA2UHF @ la1k.no.

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.

Special Callsign, LM100UKA

 

In September and October, we will be running the special callsign LM100UKA to celebrate the 100-year aniversary of the UKA-festival.

The UKA festival is a festival that has been arranged by students at the Student Society of Trondheim once every second autumn since 1917 (except for the war years of 1941 and 1943). The festival originally grew out of a student revue at the student society, in the early days lasting a week hence the name (“uka” translates to “the week”). The revue is still an integral part of the festival to this day, but the festival has grown to last for three weeks and now includes multiple concerts and various social arrangements.

This year, artists who will be performing at the festival includes Highasakite and Cashmere Cat. To get more information about the festival, please check out https://uka.no/ (Norwegian).

 

Updates on the SSTV project

After a long break, Henrik LB5DH and I decided to start working on the SSTV project again.

This time we wanted to look on how we wanted to mount and secure the antenna up on the roof.

Handmade foot

We found an old foot on the loft, which seems to work well for our installation.
We later found that we could rest the antenna on the roof without it, but in the finished installation we will be sure to make use of it.

The antenna after taking it down

The mounting solution

For mounting the guy wires we drilled two holes through the pipe on the opposite sides of each other.
This way we got four points for securing the mast. Luckily we already had structures on the roof to secure it to.

Temporary length of wire added

The issues came when trying to tune the antenna. Even though the antenna tuned fine inside, it gave us different results with the best SWR around 100Mhz when we took it outside.

This drop was the closest to 1:1 ratio we could find.
We tried adding more spools, extending the wire etc with not too good results. We did have a drop at about 3-4 in SWR around 10-11Mhz, so we seem to be close.
It does seem like the antenna isn’t reading it’s full length, so we’ll have to do some more calculations before proceeding with mounting the antenna.

We’d also like to mention that the SDR dongle has arrived, and initial testing has showed us that the direct sampling technique will work adequately for us.
More info about this and the antenna is coming soon!

-LB0VG

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