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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.

How we built LA2SIX

In January we wrote about our plans to deploy the 6 m (50 MHz) beacon LA2SIX. This week we are back to talk a bit more about the inner workings of the beacon, and to announce that our application for frequency and callsign has been approved. 🙂

LA2SIX will be fully operational from summer 2019, with initial tests starting as soon as the mountaintop beacon location has thawed. It will operate on 50.488 MHz, with 25 W into an omnidirectional antenna (vertical dipole) using the CW sequence “LA2SIX JP53EG BEEEP”.

The meat of this post is the construction details for the beacon. We started off with a paper sketch, which in this case turned out to be a very close estimate for the end product (not that surprising, considering we lost the original sketch and re-made it based on the final product).

LA2SIX beacon sketch

We have had a lot of success with the LA1K CW beacon platform. When preparing for LA2SHF (our 23 cm beacon, which is currently not operative due to an interference issue) we made an additional beacon card, so we were ready for another rapid beacon build.

Other time-savers were the off-the-shelf filter and amplifier modules. EB104.ru have a lot of cool and affordable stuff. For this project we chose a low-pass-filter they sell (27$) for the 6 m band. Its 2 kW rating is definitely overkill, but hey – it was cheap.

The amplifier was a bit harder to find, as a lot of gain is needed to be able to go to 25 W from the 10-70 mW the CW beacon delivers. We reached out to PCS-Electronics, a store that sells various FM and TV transmitter equipment. They have a “High gain” pallet, which can be ordered for specific frequency ranges if you get in touch with them. This turned out to be a very economical solution, and we ended up paying 99,- EUR for a custom tuned amplifier. They also shipped the device very quickly, and we can absolutely recommend them for other projects.

After finishing the cabling work, we made some quick voltage checks before starting to trim up the output power. The amplifier made it easy to reach our 25 W target, no real problems were encountered – that is a first!


Future blog post spoiler: LA1K 5-pole diplexer template, which will be available open source.

As a small spoiler for a future post, we also received the boards for the diplexer (ignore the silkscreen typo!). This will allow us to combine the two beacons to be able to work on the same antenna, as we mentioned in the previous post on LA2SIX.

We look forward to getting the beacon installed, and are eager to receive the first signal reports.

Getting ready for E̶s̶’̶H̶a̶i̶l̶2̶ QO-100: Part 2 – How we did it

As we’ve previously blogged [1,2] – Es’Hail2, the first Geostationary satellite to carry an amateur radio transponder has been launched, and we’ve been excited to build a setup for working QSOs on it.

The amateur transponder onboard the satellite was commissioned as QO-100 earlier this week. After its opening, the satellite was made further available to the public by WebSDRs provided by BATC and PY2GN,PY2PE. These prove to be tremendously helpful when getting set up for communication on QO-100.

QO-100 is a geostationary linear transponder that has its uplink on 2.4 GHz, and its downlink on 10.5 GHz. These are bands that the average amateur radio operator have little experience with (including us), so we figure that it might be helpful to others to hear a little about how we have gone about solving this “problem”.

Block schematic of our QO-100 setup.

Our approach to QO-100 is the GOTA approach – Get On The Air, then improve it. We get to cut a lot of corners, since we are lucky enough to have a lot of hardware to throw at the problem. Previously, we received a donation of multiple USRPs, and we also have the amplifiers we need from previous projects. The USRP is a Software Defined Radio (SDR), which is useful when dealing with large swaths of frequencies at once.

We decided to solve RX and TX with two independent device chains. This is convenient, as it allows us to disregard sequencing between RX and TX, making our setup a little easier. It also gives us a setup that is full-duplex – which is unnecessary, but nice to have as we can monitor ourselves while we transmit. Further, we decided that it would be a good idea to add some spatial isolation between TX and RX, so that the receiver is not damaged by the high transmit levels.

On the transmit end of things, we start off at the output port of the USRP N210. We need some amplification to get the USRP signal to the recommended 10 W, as the USRP N210 will only deliver approximately 100 mW. The amplifiers we have require around 1 W drive for 10 W output power, so we need an intermediate gain stage as well.

Homebrew 10 W 2.4 GHz amplifier built by LB7RG, LB1HH and Hans Theodor.

Quite regularly, LA1K members attend a course at NTNU where the semester project is to design a 10 W 2.4 GHz amplifier. These tend to be a bit funky, as they are usually rookie designs. In particular, they sometimes like to oscillate fiercely. Our amplifier drawer housed a promising specimen from a previous student project in this course. It looked to be adequately decoupled, which hopefully should keep it well-behaved.

We decided to play it safe, and use the more expensive DB6NT amplifier as a gain stage for the homebrew amplifier. This way, in case something went horribly wrong with the homebrew amplifier, it would only blow up itself, sparing the DB6NT from harm.

Lab testing of the TX amplifiers.

After some bootstrapping we had a prototype to try out on the bench. We calibrated the gain levels from the TX USRP N210 using GNU Radio and a spectrum analyzer, allowing us to associate the gain value in the software to a known power. We found that a USRP gain setting of between 20 dB and 25 dB would produce the desired 10 W output power. Somewhat concerning was that fact that the homebrew amplifier started to self-bias when driven beyond 25 dB gain, so things might get pretty funky if we go further into overdrive.

TX USRP, amplifiers and power supplies installed below the 3 m dish.

We have a 3 m parabolic dish that we use for EME and other projects. We wanted to use the dish to transmit to QO-100 – but we were lacking a suitable feed. The satellite requires Right Hand Circular Polarized (RHCP) signals on its uplink, so we built a Left Hand Circular Helix 2.4 GHz antenna which we pointed into our 3 m dish. The parabolic dish reverses the circular polarization, so that transmitted LHCP is transformed into RHCP when reflected in the dish.

Instructions for the helix were found on this collective article on qsl.net. We made some modifications to fit our requirements. Most notably we only used 7 turns, and we also went for a simpler matching structure. Our matching structure was originally intended to be a quarter-wave transformer using the first part of the helix, but it turns out that in our particular case best match was achieved without any matching structure at all :D.

DIY LHCP 2.4 GHz Helix mounted next to our 23 cm septum feed.

After mounting the helix, we turned on the power amplifiers, connected to the USRP, and started steering the 3 m parabolic dish towards the assumed bearing of QO-100. To assist with aiming, we used the WebSDRs previously mentioned to see if, and where, our signals were showing up. Using the motorized mount on the 3 m dish made it quite easy to align the antenna to QO-100, and we were quickly able to see our own signals.

The receive chain is solved by use of a commercial X-Band Low Noise Block Downconverter (LNB), which we placed at the center of a previously erected TV-dish which is no longer in use. We made a DC-injector (details about this can be found in this post) to be able to provide the LNB with the 12 V / 18 V it needs over the coaxial cable. Inside our shack we placed a lab supply along with a USRP N210 with a WBX-40 daughterboard. This serves as our receive chain, which we are able to access using the GQRX software provided by OZ9AEC.

In our last post on this subject we had some issues with pointing our RX-dish towards the satellite. Partly this was because the beacons were only briefly available, since the satellite was at the time not yet commissioned, but mostly it was because we had the satellite bearing way off. The bearing became much easier to find after we had pointed our 3 m parabolic dish towards QO-100, and were able to use it as a reference for where to point.

We used a portable spectrum analyzer to be able to monitor the satellite while attempting to align the dish. The photo shows what it looks like when there is no satellite, this seems fitting for our earlier efforts 🙂

With both RX and TX chains in place it was time to test the system. After brushing up on the operating guidelines for the narrowband transponder, we were ready to attempt the first QSO. We had some trouble creating a good SSB transmitter within GNU Radio, so we ended up working the first QSO using a very rudimentary CW transmitter.

Very rudimentary GNU Radio CW Transmitter. A button toggles a constant between 0 and 1, we multiply this with the signal source in order to turn it on and off. This allows CW operation by rapidly slamming the spacebar.
Left: GQRX receiving QO-100. Right: Rudimentary CW transmitter interface.
LA1BFA working CW on QO-100. Poor spacebar 🙁

Shortly after the video above, we made our first QSO, which was with IZ2CPS.

2019-02-19 17:51:20: IZ2CPS @ 2400080.0 CW SNT:579 RCVD:579 (OP LA1BFA:
QO-100 SAT 1st QSO LOC JN45SS RX: 10489807.6MHz)

Now we need to work on improving the station, in particular our ability to transmit SSB so that we are able to access that portion of the satellite. Nevertheless, we hope that this has given some insight into how we have gotten our signals onto QO-100, and hope that many more hams will join us in this fun project in the future. We will return with a comment on this post once we work the first SSB contacts later in the week.

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