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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.

The annual “spring trip to Vassfjellet leads to discovery of broken beacon” blogpost

This weekend we finally had the opportunity to go to our beacon site at Vassfjellet, as the snow had thawed at last (or so we thought). Our plans were to install the newly constructed 6 m beacon, LA2SIX, and assess what had happened to the site over the winter.

We have not been able to hear LA2VHF/4, our 4 m beacon, for a while. This was disconcerting, as it might mean that the antenna which we planned to co-use for LA2SIX had suffered some damage during the winter.

100 m from the summit, we encountered the first and only pile of snow on the road. Unfortunately this was enough to foil our plans, and the rest of the trip had to be made on foot.

ARK’s beacon cabin.

Once we reached the top, we were surprised to find that the vertical VHF antenna was missing. Luckily, some passerby’s had placed the antenna in a secure location nearby, so we were able to retrieve it.

Apart from thorough carbonization of base and antenna contacts (probably due to beacon transmissions during the fault scenario) the antenna seemed relatively intact. The failure seems to have happened due to our lack of maintenance on the set screws which keep the antenna from unscrewing itself in heavy vibraton/wind. Nothing bad to say about the antenna, though, as it lasted 7 years without maintenance in conditions that have proven themselves extremely harsh.

We attempted to clean up the antenna as best we could, and re-installed it on the base. Our efforts were in vain, however, as the antenna reported more than 10:1 SWR across the band.

Antenna analyzer result is a textbook example of bad SWR.

Unfortunately we need to announce that LA2VHF/4 will be temporarily offline while we perform repairs to the beacon and antenna. We have brought LA2VHF/4 back to the lab bench for a thorough examination, since transmitting into an open load for an extended period of time is bound to have caused some damage to the finals.

We have set plans in motion to be able to fix both beacons, hopefully in time to get the most out of this summer’s sporadic E season. We hope to return soon with an update on this matter.

LA1K 5-Pole Diplexer board

In the start of January, we wrote about our plans to deploy LA2SIX at Vassfjellet, where LA2VHF/4 and the other beacons are. We have an antenna which is resonant on both 50 and 70 MHz, so we just needed a diplex filter (diplexer) with the appropriate frequency response in order to connect both LA2SIX and LA2VHF/4 to the same antenna. The diplexer ensures that the output of the beacon goes to the antenna, and not to the other beacon.

To accomplish this, we made a simple PCB to hold a 5-pole lowpass/highpass style diplex filter. The project is rather simple, so it can be argued that a vero-board or similar would be a more appropriate solution. However, the PCB implementation makes for much better grounding, which in turn helps with heat transfer – increasing the power that can be run through the board. It also looks pretty. 🙂

The unpopulated diplex filter board.

If you want to use the board, it is available open source over at GitHub.

We populated the PCB with component values tailored for our 4m and 6m beacons. This is seen below. The realized board gives about 0.3 to 0.5 dB loss, and has excellent match for the desired band. Some tuning, i.e. pulling on the inductors, will probably be required for optimal performance.

Schematic sketch

Capacitors are all Johanson Technology S42E series (1111 EIA size high voltage RF caps). We used the 500 V rated variant for this design, which should allow for more than 100 W throughput. The coils are annotated with number of turns of 0.71 mm enameled wire around a permanent marker (15 mm diameter).

With the diplexer completed, we are ready to deploy LA2SIX at Vassfjellet. Now we just need the snow to thaw. The weather has been nice lately, so hopefully we will be able to get up there in a month’s time.

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