![\"\"](\"https:\/\/nolle.engineering\/wp-content\/uploads\/2026\/10\/fig2_skymap.png\")
A helix pointed at the zenith therefore covers the part of the sky with the fewest satellites. Tilted down toward the north, the main beam covers the region where they spend most of their time.<\/p>\n\n\n\n For our 3-turn RHCP helix (half-power beamwidth about 64°) on a fixed mount: about 30° elevation, facing north. 25–40° gives nearly the same result, and the azimuth is not critical within 30–45° of north. With a weak receive chain (long coax, no preamp at the antenna) or obstructions to the north, 40–45° is the better choice. Most of the improvement comes from the tilt itself; facing north adds a smaller amount.<\/p>\n\n\n\n In the simulation (current elements, SGP4, 24 h, 48° N, satellite power pattern fitted from the SatNOGS data), the tilted helix has at least one decodable satellite in view 1.5 to 2.5 times as often as the same helix pointed at the zenith, and the longest gaps between usable passes are much shorter. The figure depends on the link margin of the station, which we cannot know in advance. With a marginal setup the improvement is about 1.1–1.3×. In none of the cases we ran was zenith pointing better.<\/p>\n\n\n\n We analysed 1035 waterfall recordings of Iridium satellites from 26 SatNOGS stations between 30° and 64° N, about 51 000 ten-second samples, each tagged with the satellite position at that time.<\/p>\n\n\n\n Standard axial-mode helix, circumference one wavelength, 12.5° pitch, wound RHCP and tuned for 1616–1626 MHz. The Kraus formula gives about 10 dBic for three turns; a real unit is closer to 8–9 dBic, and the simulation uses 8.5 dBic. We also modelled a 2-turn version with a wider beam. It does not do better than three turns once the antenna is tilted.<\/p>\n\n\n\n 80 current Iridium-NEXT element sets (Celestrak), propagated with SGP4 over 24 h in 10 s steps for 48.1° N, 8° horizon mask. Helix modelled as a cos^q main lobe matched to its beamwidth. Satellite EIRP versus off-nadir angle fitted from the SatNOGS burst levels, with a bootstrap band; decode threshold varied by ±3–6 dB around a nominal value. Ratios between pointings are more reliable than absolute coverage figures. Waterfall data: SatNOGS Network (Libre Space Foundation), CC BY-SA 4.0.<\/p>\n\n\n\n For decoding we refer to iridium-toolkit (CCC Munich) with gr-iridium or iridium-sniffer as the demodulator. It decodes ring alerts, paging and messaging, ACARS and, with an AMBE vocoder, voice. It needs an SDR covering 1616–1626 MHz and runs on Linux.<\/p>\n\n\n\n Nolle Engineering, October 2026.<\/em><\/p>","protected":false},"excerpt":{"rendered":" Pointing study for receiving Iridium with a fixed 3-turn L-band helix: about 30\u00b0 elevation facing north, compared with SatNOGS recordings.<\/p>","protected":false},"author":3277,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-16362","page","type-page","status-publish","hentry"],"yoast_head":"\n![\"\"](\"https:\/\/nolle.engineering\/wp-content\/uploads\/2026\/10\/fig4_beam_on_river.png\")
![\"\"](\"https:\/\/nolle.engineering\/wp-content\/uploads\/2026\/10\/anim_north_vs_zenith.gif\")
Recommended pointing<\/h2>\n\n\n\n
Expected improvement<\/h2>\n\n\n\n
![\"\"](\"https:\/\/nolle.engineering\/wp-content\/uploads\/2026\/10\/fig3_pointing_page.png\")
Comparison with SatNOGS recordings<\/h2>\n\n\n\n
\n
![\"\"](\"https:\/\/nolle.engineering\/wp-content\/uploads\/2026\/10\/fig5_emp_presence_ns.png\")
![\"\"](\"https:\/\/nolle.engineering\/wp-content\/uploads\/2026\/10\/fig7_emp_eirp.png\")
Antenna<\/h2>\n\n\n\n
![\"\"](\"https:\/\/nolle.engineering\/wp-content\/uploads\/2026\/10\/fig1_pattern.png\")
Open points<\/h2>\n\n\n\n
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Method<\/h2>\n\n\n\n
Decoding<\/h2>\n\n\n\n