quadrifilar helical antenna

2 Articles

3D Print Your Next Antenna

February 19, 2021 by 40 Comments

Building antennas is a time-honored ham radio tradition. Shortwave antennas tend to be bulky but at VHF frequencies the antenna sizes are pretty manageable. [Fjkaan’s] 2 meter quadrifilar helicoidal antenna is a good example and the structure for it can be created with 3D printing combined with electrical conduit.

Many people, including [G4ILO] use PVC pipe for the structure, and that design inspired [Fjkaan]. Despite being a bit less substantial, the conduit seems to work well and it is easy to cut. The helical design is common for satellite work owing to its circular polarization and omnidirectional pattern.

Continue reading “3D Print Your Next Antenna” →

Eavesdropping On Cosmonauts With An SDR

March 28, 2019 by 9 Comments

Usually when we hear about someone making contact with astronauts in orbit, it’s an intentional contact between a ham on the ground and one of the licensed radio amateurs on the ISS. We don’t often see someone lucky enough to snag a conversation between ground controllers and a spacecraft en route to the ISS like this.

For [Tysonpower], this was all about being in the right place at the right time, as well as having the right equipment and the know-how to use it properly. Soyuz MS-12 launched from Baikonur on March 14 with cosmonaut [Aleksey Ovchinin] and NASA astronauts [Nick Hague] and [Kristina Koch] onboard, destined for the ISS after a six-hour flight. The lucky bit came when [Tysonpower] realized that the rendezvous would happen when the ISS was in a good position relative to his home in Cologne, which prompted him to set up his gear for a listening session. His AirSpy Mini SDR was connected to a home-brew quadrifilar helical (QFH) “eggbeater” antenna on his roof. What’s nice about this antenna is that it’s fixed rather than tracking, making it easy to get on the air with quickly. After digging around the aviation bands at about 121 MHz for a bit, [Tysonpower] managed to capture a few seconds of a conversation between [Ovchinin] and Moscow Flight Control Center. The commander reported his position and speed relative to the ISS a few minutes before docking. The conversation starts at about 1:12 in the video below.

We think it’s just cool that you can listen in on the conversations going on upstairs with a total of less than $50 worth of gear. Actually talking to the hams aboard the ISS is another matter, but not a lot more involved really.

Continue reading “Eavesdropping On Cosmonauts With An SDR” →