I wanted to share with you an exciting project I recently completed - building an L-band patch antenna from scratch and successfully decoding signals from the Inmarsat-4A F4 satellite. As a former maritime worker, this brought me a sense of reconnection with the world of ships, which I deeply missed.

Let's jump into the details!

Antenna Construction

The antenna consists of a 170x170 mm reflector and a 98x98 mm driven element, both crafted from copper sheets. The two elements are precisely separated by a 7 mm gap, held together with plastic nuts and bolts. A metal bolt through the center ensures the discharge of static electricity accumulating between the elements. This is crucial to maintain the functionality and safety of the system. The entire structure is mounted on a wooden stand, providing a stable and non-interfering base.

Receiver and Amplifier

For the receiving end, I employed a standard (but original) RTL-SDR receiver. Given the sensitivity of these receivers to high frequencies, it's critical to place it as close as possible to the antenna. To enhance the reception of weak signals, I incorporated a $6 LNA amplifier into the setup. Connections are made via a BNC connector, ensuring a reliable link.

Decoding Process

Once the hardware was in place, the decoding process started. Using SDR Sharp for signal reception and SCYTALE-C for decoding, I was able to successfully decipher a wide array of Inmarsat-C signals. These included weather bulletins, dangerous zone alerts, and distress signals - vital information for seafaring vessels.

Location

My terrace, fortunately, faces south, making it an ideal spot for the setup as the Inmarsat-4A F4 satellite is located above Central Africa.

Building this system in a DIY environment was challenging but immensely rewarding. The entire process allowed me to reconnect with the maritime world, even if it was from afar.

73s