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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:

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 ~35 W 1/2 wl vertical Linear (vertical)

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

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

Latest posts on LA2SHF

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. The beacon is 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 consists of “LA2SHF JP53EK” and a long tone.

(Note: Wrong locator is currently issued as of 2018-04-08, see LA2VHF/4 and LA2SHF QRV from Vassfjellet.)

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.

LA2SIX (License pending) beacon, and plans for the coming year

The beginning of a new year is a good time to step back and think of the things that will be interesting to work on in the coming months. As long-time readers might be aware, we have a thing for amateur radio beacons. Currently we are very excited by one particular idea: getting early indications on sporadic propagation modes by watching them progress through the lower frequency bands.

One thing we have watched with curiosity is how certain propagation modes have a maximum usable frequency, and how some ionospheric phenomena will cause this frequency to suddenly start creeping upwards. The idea is that by having appropriately placed beacons, we can get an idea of when the bands are open at our location by seeing how they are received either through WebSDRs, or by collecting reports on DX clusters.

Our pipedream is having a beacon bank with beacons covering every 10 MHz from 30 to 80 MHz. This would allow us to do some really interesting statistics such as how often an increase in maximum useable frequency from none to 30 MHz leads to a further increase from 30 MHz to 40 MHz.

This is currently somewhat unlikely – it would take a lot of time to build all the beacons, and many of these frequencies are not within an amateur radio band. There are however movements across the world for licensing in the 40 MHz and 60 MHz bands, so this might not be as far-fetched for the long term as it seems at first glance. For instance, Ireland recently got amateur radio allocations in the 40 MHz and 60 MHz bands and UK and Denmark have approved beacons on 40 MHz previously.

For now we are focusing on the bands we already have access to. As a start, we have our beacons LA2VHF and LA2VHF/4, which cover 144 MHz and 70 MHz, respectively. The natural expansion in Norway is the 6 m band at 50 MHz.

For this blogpost we actually did some work beforehand. The beacon is already finished, and we have applied for the license and frequency allocation. We are hoping to get all the documentation in order by spring/summer, when the conditions at Vassfjellet should allow us to install it. Typically our beacon location is inaccessible during the winter, due to snow covering the mountaintop at which it is situated.

Sneak peek of LA2SIX’s (license pending) innards.

We will come back to the technical details and how we built the beacon in a later blog post.

For the antenna we will use the same vertical that we use for LA2VHF/4, which is a magical superwideband antenna of unknown origin, presumably looted from a military or marine surplus storage.

To use both beacons on the same antenna we will also need to cook up a simple diplexer before summer, so that should be a fun little experiment for a future post.

We have our fingers crossed that we get the paperwork in order, and with some luck we will have LA2SIX in active operation in time for the summer sporadic-E field season.

 

LA2SHF temporarily QRT

We’ve identified unwanted spurious emissions from LA2SHF when installed at Vassfjellet, and taken it down for the time being. While not critical, and the spurs technically being below the limits, we’d rather play safe and also satisfy our inner engineering pride. In this post, we outline a likely source of the spurs (they are actually another morse signal, and can be identified as LA2VHF/4), and describe LA3WUA and LA1BFA’s expedition to Vassfjellet last week when they went to bring LA2SHF back home.

Detective work in the RF plane: Diagnosing the spurious emission problem

Back when LA2SHF was built, it was designed to suppress its unavoidable harmonics down to an acceptable level of around 40 dB below the main signal level.

Measurements in the lab, showing LA2SHF in the main, central peak, and its first and second harmonics to the sides. The height of one square corresponds to 10 dB.

Measurements on the lab bench could confirm that the suppression was at around 40 dB and acceptable, and that our beacon child safely could be installed at Vassfjellet. All was well, until we in September were notified by email that our sidebands were not behaving very nicely, but were bullying their surroundings with too much power in the wrong frequencies.

We checked a measurement from Samfundet using the parabolic dish, and mostly, the beacon had the nice, expected ~40 dB suppression of the sidebands:

Sometimes, however, there were emissions at the sidebands that were suppressed down with only ~20 dB:

This was not something which was observed at the lab bench. Sometime after installation at Vassfjellet, the beacon started behaving differently than the earlier observed behavior.

The waterfall plot could confirm this trend, with a sideband peak going up and down to the right and left of LA2SHF (beacon signal in the center).

Plotting two timesteps with high and low sidebands shows the variation in sideband strength.

Sidestep: Interestingly, the peaks shift approx. 0.5 kHz from low to high. The high peak still has features from the low peak, and it is almost as if it is a different peak entirely that gets merged with the previous peak:

The sideband is close to 62.8 kHz from the LA2SHF frequency, while the spur is close to 63.2 kHz from the LA2SHF frequency.

Plotting the frequency bins corresponding to LA2SHF and the first peak as a function of time partially explains the behavior, and why it wasn’t discovered until installation at Vassfjellet. The peaking behavior with ~20 dB increase in the first harmonics is actually an entirely different morse signal altogether! This could also partially be seen in the waterfall diagram above, as the pattern in the sideband peaks were uncannily regular.

Plotting up the full morse signal in the sideband bin reveals that the callsignal is LA2VHF. We have two beacons that use LA2VHF, LA2VHF and LA2VHF/4m, but only one of these have the same timing speed as LA2SHF, i.e. LA2VHF/4m. The morse signal is clear only when LA2SHF is turned on, and is otherwise on par with the noise level, but the revealing V-s are still identifiable.

The working theory is that LA2VHF/4m is injected into the reference for LA2SHF somewhere along the transmission chain, and that this leads to the LA2SHF sideband having characteristics from LA2VHF/4m. The beacons LA2SHF, LA2VHF/4m and LA2UHF share a 10 MHz reference, which might have been “contaminated” with the signal from LA2VHF/4m.

The synthesizer does some digital tricks in order to get a 1296.963 MHz signal. These digital tricks do not always produce a clean signal, but a signal containing spurs – and one of these spurs is likely the sideband we see around LA2SHF. Which spur mechanism it is, however, is something we need to figure out. We think it might be related to the seventh harmonic of the reference (i.e. 70 MHz). Somewhere along the line, LA2VHF’s 70.063 MHz signal gets added on top of the 70 MHz harmonic of the reference, and we get a CW-modulated spur. The small frequency shift we see in the spurs should also somehow be related to this.

We couldn’t see this behavior at the lab bench since there were no strong signal sources with the right frequency nearby.

Vassfjellet trip

LA1BFA Magne and LA3WUA Øyvind went on a roadtrip to Vassfjellet on Monday last week in order to see whether the problems could be debugged and fixed in situ.

On the way up to Vassfjellet with a lot of snow in the road. Winter is here :-(. Photo: LA1BFA Magne.

Antenna covered in snow. Photo: LA1BFA Magne.

A view of our beacon cabin. Photo: LA1BFA Magne.

Another view of the beacon cabin. The window shutters have fallen off, and the ropes are no longer tight. Photo: LA1BFA Magne.

Unfortunately, the problems weren’t immediately fixable after having verified the problem on the spot and tried a couple of possible measures. Night was fast approaching and the weather was starting to get bad, so they took the beacon back to Samfundet again for the time being. We’ll investigate it and try to reproduce the interference problems in the lab, and put the beacon up again before winter starts in earnest. The weather is currently slightly cold and stormy, and we expect that we will have to wait for quite a few mild days before the road is clear from snow again and we can return.

A couple of other problems that became apparent during this trip is that the shutters have fallen off one of the windows, and that the cabin might have sagged a bit, judging from the ropes tying it down. We will have to replace the shutters before winter, otherwise the beacons are in for a hard time during the worst winter storms.

This post ends on a slightly negative note, but we remain hopeful that we will prevail with fixing both beacon and cabin before it is too late :-).

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