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June 26, 2011
On average, an Iridium satellite is visible for about 10 minutes; SBD transmission or reception are usually less than 30 seconds, and once that satellite is beyond the horizon another is in view. One of the advantages of the Iridium constellation of satellites is that a transceiver is usually in the footprint of 1-3 satellites at any time, literally worldwide.
Yes, the 9602 has a Ring Indicator line which goes high when a message is available, you don’t have to poll for message availability (known as a ‘mailbox check’). No, it doesn’t automatically receive messages, since sending or receiving messages incurs a charge.
It’s not a good idea to mess with the RF path, as this can cause a multitude of issues including everything from weak reception, interference problems, up to destroying the transmitter. RockBLOCK sells a version with an SMA connector instead of on-board antenna. It would be best to use an Iridium approved antenna. Patch antennas work OK and are inexpensive, but helical antennas usually perform best, and have a better ‘look’ angle.
The phrase “clear view of the sky” deserves a bit more explanation. Due to the physics of satellites orbiting the Earth, Iridium satellites spend much of their time fairly low on the horizon from the viewpoint of a transceiver. The angle above the horizon where an Iridium satellite is most likely to be located at any particular time is roughly 10-20 degrees depending on your latitude. While they do pass directly overhead, they are traveling at their highest rate of speed, relative to a position on Earth, and therefore visible for the shortest time. The Iridium transceivers must also compensate for Doppler shift, which is greatest directly overhead. Iridium satellites travel almost exactly north-south or south-north; so if the transceiver is located in, say, a canyon running east-west then sending and receiving an SBD message may be more challenging than a canyon running north-south.
The upshot of all this is that just because you can see a good portion of the sky doesn’t mean you have ideal conditions to communicate with a satellite, especially if you’re down in a hole. Usually an SBD session lasts less than 30 seconds, so even a limited view of the sky might be sufficient for your application.
about 5 years ago
Does anyone know if the Color LCD Shield (LCD-09363) will fit in this enclosure without too much hacking? It looks like the bulge for the ethernet jack might be where the edge of an opening would need to be cut.
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