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Background

I'm doing some research on a company called ASTS who claims to be able to connect to regular smartphones from a satellite. Initially I wrote off their claims, but after looking into it a bit more (along with some link budget calculations), it actually seemed... surprisingly possible.

To my surprise, this wasn't even actually the first time this has been done. Apparently a company called TerreStar was able to connect to a smartphone back in 2010, from GEO! I've always imagined satellite phones to be big, bulky, power-hungry devices.

Out of curiosity I bought a used TerreStar Genus to take apart, just to see how big the antenna is - especially since it's talking to a GEO satellite. I'm having trouble locating it though, can anyone help?

So far I found some rf amplifiers, but not the actual antennas themselves...

SKY65124-21 - RF Amplifier 1930-1990MHz 2W 5Volt -40C +85C

SKY77340-21 - The SKY77340 Power Amplifier Module (PAM) is designed in a compact form factor for quad-band cellular handsets comprising GSM850/900, DCS1800, PCS1900, supporting GMSK and linear EDGE modulation.

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More pictures here (and also available upon request): https://i.sstatic.net/PJ1cv.jpg

Updated Question

Wait, I think I found them! Are these it? Wow, I'm honestly shocked these tiny things are able to transmit to GEO. Is the antenna that's connecting to the satellite the E000118 REV F one since that's the only one that's above the line?

Going by the 2 rf amplifiers I found, does this mean that the antenna had a max output of 2W?

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    $\begingroup$ Assuming 1950MHz, back of the envelope calculations is a quarter wavelength would be ~3.9cm? Though, antenna design gets really strange at these frequencies. Anyway, feel free to self-answer if you think you found 'em. $\endgroup$
    – user21417
    Commented Feb 18, 2022 at 2:09

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You can see five rf connections to off-board antennas, all around the board. Each connection has a "hot" and a ground, because the antennas are variations of the Inverted F antenna. Most of the antenna PCBs look like FR4, which is not ideal.

The satellite antenna is probably the thing in the centre of the back shell just below the camera hole, above number 21 on your cutting pad in the second photo. This is the prime antenna position.

It makes contact with the two spring contacts on the right of the board, below the alert/vibrate motor. Note how there is no ground cut-out below these two contacts, unlike all the other antennas, so the back centre antenna must be a different design.

Edit Maybe that's a loudspeaker. It looks like it from some intact phone photos. Though the traces connecting to it are quite RF-like, they wouldn't bother doing that for a speaker?
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If it is the monopole/IFA called E000118 then another clue is that the RF trace to the external antenna connector runs all the way around the camera and down to nearby the same RF can.

Inmarsat isatphone is a handheld phone using GEO satellites. It's been around since before 2010. It has a flip-up quadrafilar helix antenna and uses an amazing 2400bps voice CODEC. Thuraya is another GEO-based service, satellites at 44 and 98 longitude only.

Cellphones long ago traded antenna performance for form factor, but when gain, pattern and circular polarisation really counts they go back to a big external antenna.

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  • $\begingroup$ I'm pretty sure the middle part is for the loud speaker. I was pretty confused too when I saw the giant contacts going to a speaker. What are PCB FR4 antennas, and why aren't they ideal though? $\endgroup$
    – 0xbad1d3a5
    Commented Feb 22, 2022 at 5:40
  • $\begingroup$ @0xbad1d3a5 FR4 is a type of PCB material. It's very common to print microwave antennas on them. $\endgroup$
    – Mike Waters
    Commented Feb 22, 2022 at 20:54
  • $\begingroup$ If you look closely, both the earphone at the top is covered by the same mesh. That thing in the back is probably a piezo speaker, and the connects are typical spring-pin connectors used in plastic handset construction. Perhaps the antenna is the round silver thing in the middle of the ground-plan. It says "06P" or "d90" depending on how you want to read it. That would be the size, orientation, and location of a stubby coil antenna we often see on high-freq stuff. $\endgroup$
    – user21417
    Commented Feb 23, 2022 at 0:37
  • $\begingroup$ That being said, just searching for "s-band antenna" will show you so-called "patch" antennas that look pretty much like that "speaker". Circularly polarized antennas. They also come in little covered stubby coils too, so the mystery is not over. $\endgroup$
    – user21417
    Commented Feb 23, 2022 at 0:45
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    $\begingroup$ I worked in a cell phone factory in the late nineties, when the phones we were making had antennas about 10 cm (4") long that could be extended or retracted. Extending the antenna improved reception by about 4 dB (which was less than one bar on the display). That was when mobile phone networks were in their infancy, and cell site antennas in cities were mounted up high. Now cellular antennas in cities are mounted down low to limit the number of users connected to the site, which is much closer now. Handset antenna gain doesn't matter nearly as much now as it did back then, as you say. $\endgroup$
    – rclocher3
    Commented Feb 23, 2022 at 1:05

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