Amateur Radio Direction Finding

This year we did the fun version of ARDF. The idea behind ADRF (which is sometimes also called "fox hunting") is to find a transmitter using a direction finder.

Two of our colleagues, who are HAM operators, used the break after lunch to hide two transmitters (transmitting on 3.1MHz) in the nearby landscape. The transmitters send their callsigns as morse code (usually MO "-- ---"). Since we did the fun version of ARDF, both transmitters were active all the time and operated on different frequencies. (The sport version of ARDF would be that both transmitters would transmit only every few minutes and would send their callsign only once.)

We formed groups by drawing lots, equipped every group with a direction finder and wished them good luck. The direction finders are portable receivers that work on both, the H- and E-field component. Using both modes allows an operator to point the direction of the source of the signal by observing the volume level of the signal in the earpiece.

The first transmitter was placed near an easy to reach parking lot. This location wasn't that spectacular. The second transmitter was hidden inside the area of an old sanatorium that burned down a few years ago. This spot gave us an exciting view on the old site and over the nearby artificial lake.

Infrastructure Review

Traveling with 28 hackers makes high demands on the available bandwidth and latency of the internet connection. Additionally for Embedded Development we need local services like a TFTP and NFS server. This means that all-in-all we need something like 100 or more DHCP leases and lots of Ethernet ports (and WiFi connectivity)!

Some of our hackers are active in the local branch of the Freifunk Initiative Freifunk Braunschweig. This year those colleagues used the mobile WiFi equipment to provide us with WiFi coverage and a multi-path uplink into the internet. Since those colleagues used the Pengutronix staff as lab mice to improve their tooling, we think this is a fair deal.

The multi-path uplink uses up to three different wireguard tunnels to a server on the internet. On top of the tunnels OSPF is used to route the actual traffic from the clients to the internet. This allowed us to plug-and-play new uplinks.

Using this we combined two LTE uplinks (on different carriers) and the landline DSL of our event location. After just a few hours we ditched the DSL uplink: a 6000kBit/s DSL just isn't state-of-the-art anymore.

During the week we generated up to 170 GB of traffic via LTE. If this sounds little: keep in mind that German mobile contracts usually come with less than 10 GB per month!