Akademisk Radioklubb


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.

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