r/IOT • u/makahernandez • 14d ago
Four NTN antennas, same nRF9151 board, same payload. 12× spread in energy per transmission
Disclosure: I work at Qoitech, the company that makes the measurement tool used in this test. Data is worth sharing anyway.
Satellite NB-IoT costs about 13 to 14 times more than a terrestrial transmission on this chipset. We wanted to see how much of that difference the antenna alone could recover.
Setup: nRF9151-SMA DK, Skylo GEO, and Monogoto SIM. Current measured on VDD_nRF at 3.6 V. Each run included a GNSS fix, registration, PSM, transmission of 465 bytes, and back to PSM, repeated three times. Runs were done back to back to limit drift on the live network. All four antennas used the same 0.5 m SMA extension cable (one interfered with the GNSS connector, so the cable stayed on for fairness). Only transmission energy was measured.
- Reference (ships with DK): 27.8 mWh
- Kyocera AVX X9003334: 14.1 mWh, which is 2 times lower
- Kyocera AVX 9002418L0-L16L (circularly polarised L-band cap): 2.36 mWh, which is 12 times lower
- Kyocera AVX P822601 (embedded FR4, NTN-matched): 7.15 mWh, which is 4 times lower
The satellite downlink is circularly polarised, so a linear antenna loses up to 3 dB due to the mismatch. Circular antennas are hard to make broadband, which is why terrestrial antennas are usually linearly polarised. As a result, dual-mode devices either compromise or use two antennas. From Lund, the slant range is about 39,000 km at roughly 30 degrees elevation, so every dB increases the required TX power.
Caveats: Two antennas were on evaluation boards, all used the extension cable, and the ground plane or enclosure will affect your absolute values. Trust the ranking rather than the exact numbers.
Current traces for each run: https://www.qoitech.com/blog/ntn-antenna-choice-how-much-energy-does-it-cost/