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LA1K / LA1ARK / LA1UKA

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Beacons: collection of technical details

Recent additions of LA2VHF/4m (2015) and LA2SHF (2018) to our beacon park at Vassfjellet has increased the number of beacons ARK maintains to a total of 4 – from 2 and then 3 to “many”. Unfortunately, information about these beacons is scattered around the blog at la1k.no, and finding information about the frequency or transmitted signal is a challenging search activity (though luckily mostly contained within the beacon tag). But challenging no more! We’ve constructed a new page at https://www.la1k.no/beacons which lists the information in an orderly manner along with the expected transmitted signal and some history, which we hope will make life easier both for ourselves and others.

Beacon containment cabin at Vassfjellet. Photo: LA3WUA.

All our beacons transmit a morse signal at a regular interval. The beacons have been useful for the study of propagation conditions at the covered bands, and for debugging and measurements of our antennas.  We plan for the future to extend to a 6m beacon if we can obtain a license for it, as well as possibly covering the entire 1-10 GHz range. We’re also making plans for extending the transmitted signal from a simple morse signal to other digital modes like PI4, to enable easier decoding under weak propagation conditions.

Beacon rack: LA2VHF, LA2UHF and LA2VHF/4m from top to the center of the rack. LA2SHF has been left outside in the cold/on the table. LA2SHF’s sleeve dipole antenna can be seen in the white tube to the left. Photo: LA3WUA.

Like already mentioned on the page: If you hear any of these beacons, let us know! We appreciate reports on DX clusters, or direct contact through email. DX cluster reports or emails from operators who have heard our beacons are invaluable in investigating propagation phenomena.

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Beacons

ARK develops and maintains radio beacons from JP53EG at the top of Vassfjellet, a local mountain. Each beacon autonomously transmits a morse signal on a specific frequency. We use these for debugging of our radio equipment and for investigating propagation phenomena. The beacons can be heard on the following frequencies:

Not in service / Historical beacons:

  • LA2SHF 1296.963 MHz (23 cm) (QRT: 2019)

If you hear any of these beacons, we’d love to hear about it! We appreciate reports on DX clusters, or you can contact us directly. Details on the equipment and transmitted signals follow below.

LA2VHF

Latest posts on LA2VHF

Multiple incarnations of LA2VHF have existed throughout the times. The current beacon in use was built by LA3JJA and LA8TKA in 1999, and has faithfully and mostly uninterrupted pushed out a long stream of timed morse sequences since then.

It has a directive antenna pointing towards the North, with the intention that back-scatter from Northern lights should reach Europe.

QRG Power Antenna Polarization
144.463 MHz 25W 6-element yagi (pointing towards azimuth 15°) Horizontal

The sent CW signal consists of “LA2VHF JP53EG” and a long tone.

LA2VHF/4m

Latest posts on LA2VHF/4m

LA2VHF/4m was developed by LA7VRA and LA3JPA, and installed at Vassfjellet in 2015. The beacon was based on a 35-4400 MHz CW exciter board designed by LA3JPA Jon Petter in 2012, which has been made open source on GitHub.

QRG Power Antenna Polarization
70.063 MHz ~25 W 1/2 wl vertical Linear (vertical)

The sent CW signal consists of “LA2VHF JP53EG” and a long tone.

LA2SIX

Latest posts on LA2SIX

LA2SIX was developed in 2018 by LA1BFA and LA3WUA. It was licensed in early 2019, and deployed for the first time in the summer of 2019. The beacon is built on top of the same beacon platform as LA2VHF/4.

QRG Power Antenna Polarization
50.488 MHz ~25 W Diplexed with LA2VHF/4 Linear (vertical)

LA2UHF

Latest posts on LA2UHF

LA2UHF was QRT for five years, until it was refurbished by LA3JPA and LA7VRA in 2015 using the same beacon platform as LA2VHF/4.

QRG Power Antenna Polarization
432.463 MHz 22W Covered 12-element yagi (pointing towards Trondheim) Horizontal

The sent CW signal consists of “LA2UHF JP53EG” and a long tone.

LA2SHF (Not in service)

Latest posts on LA2SHF

LA2SHF is out of service for the foreseeable future due to interference issues with a primary allocation user.

The LA2SHF license was obtained already in 1979. A working beacon was made in the 1980s, but had to be taken down due to interference with an air traffic control radar at Gråkallen. In 2017, the need for a 23 cm beacon resurged due to activity in the 1 to 10 GHz project, finally culminating in a working beacon in January 2018 thanks to work done by LA3WUA and LA1BFA. The beacon was installed at Vassfjellet in June 2018, but had to be shut off permanently in 2019 due to new interference issues with a primary allocation user. The beacon was built on top of the same beacon platform as LA2VHF/4.

QRG Power Antenna Polarization
1296.963 MHz ~30 W Sleeve dipole Linear (horizontal)

The CW signal consisted of “LA2SHF JP53EK” and a long tone.

Beacons

ARK develops and maintains some radio beacons from JP53EG at the top of  Vassfjellet, a local mountain. The beacons can be heard on the following frequencies.

LA2VHF/4m 70.063 MHz
LA2VHF 144.463 MHz
LA2UHF 432.463 MHz

If you hear any of the beacons we would love to hear about it at la2vhf or la2uhf@la1k.no.

 

Back in 2012 Jon Petter, LA3JPA, designed a 35-4400 MHz CW exciter board (seen in the left picture below) that is the main building block used in the LA2VHF/4m beacon. The CW beacon project is made open source and can be found on this github page.

The cabin that houses our beacons is placed near the foot of a 196 m tall telecommunications tower. When icicles fall from this height they have a tendency to pierce the roof on our cabin, therefore we reinforced the roof with steel plates (building progress seen to the right above) in the summer of 2016.
We also got a working 5.8 GHz data link between the cabin and our main shack at Samfundet. As soon as the snow melts and we have access to the mountain top again we will work on improving the stability of this link.

Upcoming changes

We also have some other exciting changes to the beacon setup. In the recent years we’ve become particularly interested in the 6m band, dubbed the magic band for the way it suddenly opens and closes. To get an indication of when conditions are good we are hoping to expand our lineup with a 6m addition to LA2VHF in the summer of 2017.
Actually we’re well underway, we’re just missing power amplifier (PA), band allocation and final integration at this point. On the PA side Jotron donated some power transistors and matching 28 V supplies, speeding up the process immensely. Another blog on the design of this PA will pop up in the months to come.

On 70 cm we’re changing the antenna from a 10 element yagi to a big wheel antenna. This is because the main mode of propagation is likely to be via tropospheric ducting, where the antenna gain at each side is not the limiting factor. The big wheel antenna is an in-phase stack of three horisontal loops, yielding an omnidirectional horisontal pattern, with improved gain compared to a single loop. This we believe will improve the chances of this beacon being heard out there as the improved tropospheric volume coverage by going from narrow beam to omnidirectional is considerable.

The big wheel is also a prime candidate for the 6m and 4m beacons, this is primarily because most operators on these bands use horisontally polarised antennas. For 2m the main mode of propagation is aurora scatter, where the antenna gain does matter. So we will stick with a yagi for this band.

Vassfjellet season begins

Our beacon site at Vassfjellet has been a topic for many blog posts in the past. It has been one of our favorite pastimes, so naturally we were excited when the snow finally started melting. At last we are able to access the site again, and are eager to see what needs to be fixed this year.

The season was kickstarted when some of our extra-eager members, LB0VG and LA2QUA, went for a winter trip there to make some quick repairs on the wifi link, and assess the health of the site in general.

LB0VG returned to the site again this Saturday. He was able to make this trip by car, which makes it much easier to haul equipment to and from the site.

The goal for the trip was to install another wifi link, this time to act as a failover for the first wifi-link. The failover link will take over once the main link dips below a certain threshold. This way, we have a method of securing continuous operation for our beacons and monitors in case of trouble.

LB0VG aiming the Ubiquiti PowerBeam for the failover wifi.

The failover link still needs some alignment to make perfect contact, but we are sure that it will work after some more tweaking. Once it is operational we are eager to detail the nitty gritty technical details on this blog.

The only technical installation that broke this year was our ADS-B antenna, which had gotten bent 90 degrees out of shape. Luckily this was rapidly repaired by LB0VG, and our ADS-B station is now back to receiving DX-like distances on passing aircraft.

ADS-B antenna 90 degrees out of shape.

Other than improvements to existing setups, the main theme for this years Vassfjellet adventures will probably be repairs to the building structure. Over the last couple of years, we have made small repairs to various things (mostly the leaky roof), but have noticed some problems that will need a more thorough refurbish. The main problem that we need to address is that the cabin has started to slant significantly, leading us to think that the foundation is compromised. Also, the roof is leaking again. 🙂 We will come back to these issues in future blog posts.

SatNOGS station slightly more QRV, but 90 degrees out of phase

Our SatNOGS station has been very QRT for a long time, first when the USRP broke down and yet more when the antenna fell down. The antenna has since been fixed, the USRP has not been fixed, but we also have an RTL-SDR we could just have plugged straight in back in March. We opted not to since having antennas tracking satellites on top of the roof would look rather bad when the rest of the Student Society was in full Covid-19 lockdown, and we might have had some problems if the antenna for some reason got stuck. This is no longer a problem, if it ever was a problem, so it was time to do something about it.

On the TODO-list was: 1) Set up the RTL-SDR, 2) calibrate the antenna heading and 3) test that everything worked as expected. 1) and 2) turned out to be quite the adventure that was so exciting that I never got to 3).

Battling against old librtlsdr packaging bugs

The baby steps of action point 1) were actually done back in March.

RTL-SDR connected to the SatNOGS NUC to the left.

Once connected, the RTL-SDR was behaving rather weirdly. The SDR was tested using GQRX, where GQRX was run over SSH, which normally causes some glitches in the waterfall display due to network latency, but the glitches were worse than anything I’ve ever seen, and I’ve seen quite a few weird waterfalls in my time.

RTL-SDR showing weird waterfall.

The “LNA gain” setting was also grayed out. Everything was working nicely on my own personal computer, however.

Nice and high signal/noise levels, no weird artifacts, and discernible CW code from one of our beacons. There was even a working LNA gain setting! Everything a man can wish for.

The internal tuner turned out not be detectable. On my own computer:

$ rtl_test -t
Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000001
(...)
Found Fitipower FC0012 tuner

On the SatNOGS computer:

$ rtl_test -t
Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000001
(...)
No supported tuner found

This was most probably due to an already fixed bug in the Debian package, which was consistent with the version available the SatNOGS Ubuntu installation and the release date of the distribution (0.5.3-13, Ubuntu LTS 18.04). Right now we have the option to upgrade to the next Ubuntu LTS version (20.04), but we didn’t have that back in March, so we quickfixed it by just installing a more recent librtlsdr package directly from the Debian repository. Not the best solution, but luckily this worked fine despite some complaints from the packaging system. Sorry, packing system, we’ll fix you more properly later on.

GQRX over SSH still has enough artifacts due to network lag to make it less than clear that the RTL-SDR now was working fine, so we have plotted the frequency bin from an IQ recording instead:

Nice and clear beacon signal! RTL-SDR working nicely. Now onto the antenna heading.

Not calibrating the antenna heading

Everyone knowledgeable about SatNOGS antenna calibration, i.e. LB6RH and LA3WUA, were either a) on a forest hike or b) refurbishing their kitchen. Leave everything to Asgeir! He can fix it and/or damage it beyond repair.

Calibration of the antenna heading can be quite a stressful event if you are all alone and forget that you have wondrous electronic tools available for adjusting the antenna without doing such stressful things.

First, you have to turn the rotor.

Then you have to walk to the ladder.

Then you have to climb the ladder.

And then you have to observe whether the antenna is pointing correctly towards the intended heading.

And then you have to walk all the way back again.

After some back and forth and challenging basic trigonometry exercises you can verify that, yes, the antenna is pointing towards Vassfjellet, our well-defined heading of choice.

This could reveal that reality’s 180 degrees azimuth corresponded to 270 degrees azimuth on the rotor controller. Time to adjust the rotor controller!

The problem is that this is not actually possible with this type of rotor controller. The rotor itself needs to be physically positioned so that rotor controller 270 degrees azimuth actually corresponds to the physical 270 degrees azimuth. Sorry, Øyvind, you mounted the rotor 90 degrees off! Finalization of this adventure will therefore have to wait until LA3WUA can finish his kitchen adventures and come back and rotate the rotor 90 degrees.

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