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I can confirm as an amateur radio operator- it's a research project. We've heard it's signals on the air, and frankly it;s the only thing it could be doing. No encoding, transmit response pattern- it was trying to map the propagation patterns in the ionosphere.

But there is a punchline: WSPRnet does the same thing for free. Really.

http://wsprnet.org/drupal/

I absolutely agree - that's why I opined that harvesting power form other, higher power external sources might be more effective.

I've done a fair bit of weak signal work on the 30m band. I once transmitted with 100mW of power using the WSPR mode from Richmond Va and a station in New Zealand received and correctly decoded it. That's a lot of km/W ! Here's a map of current activity.

...it could be fertile ground for experimentation...

It is a fertile ground for experimentation! You need look no farther than the recent influx of extremely spectrum-efficient modes developed by K1JT. He's developed modes tailored for most any propagation mode/band including meteor scatter, moonbounce, etc.

The newest of the lot, the JT9 modes, are capable of decoding signals as far as 42dB into the noise!. The fastest JT9 mode takes 1 minute per transmission but can decode at a S/N of -27dB - that's noise with 500x the power of the signal.

Take a look at the WSPR page - on it you can access a database of WSPR transmissions, some of them at amazingly high km/Watt ratios.

...it could be fertile ground for experimentation...

It is a fertile ground for experimentation! You need look no farther than the recent influx of extremely spectrum-efficient modes developed by K1JT. He's developed modes tailored for most any propagation mode/band including meteor scatter, moonbounce, etc.

The newest of the lot, the JT9 modes, are capable of decoding signals as far as 42dB into the noise!. The fastest JT9 mode takes 1 minute per transmission but can decode at a S/N of -27dB - that's noise with 500x the power of the signal.

Take a look at the WSPR page - on it you can access a database of WSPR transmissions, some of them at amazingly high km/Watt ratios.

This is similar to how you sometimes hear VHF FM Radio across multiple states - most of the power "escapes" into space but enough bends around the earth that it can be heard on the ground.

I'm an Amateur Radio operator and understand the concepts of tropospheric ducting and other propagation-related phenomena. You can't rely of any propagation mode other than line-of-sight at VHF or UHF frequencies. Even one of my favorite ham bands, 10m (~30 MHz) is slavishly reliant on the Sun for propagation. Right now it's dead as a doornail. When the Sun is in high gear, I've talked to other hams in Russia on 25W while I was driving down I-64.

Your supposition of iPads needing 18dB antennas is specious (although 18dB gain at sufficiently high frequencies is easy) - look at your average cell phone. It puts out <= 600 mW and the antenna likely has negative gain, but I can still be 'heard' by cell sites 20+ miles away. Antenna gain is reciprocal - if an antenna has 18dB gain on transmit, it also has the same gain on receive.

For another example, look at space probes. The Voyager probes have relatively large antennas and rather meager transmitters, but by using the enormous dish antennas here on Earth we can still hear them over 17.2 x10^9 km.

If you want to look into weak signal modes and propagation at HF, check out http://wsprnet.org/drupal/wsprnet/spots . We are doing other-side-of-the-world comms using much less than 1 Watt ERP.

If you're interesting in such things, look into the research Amateur Radio operators have done into HF radio protocols such as PSK31, TOR, Clover, MFSK16, etc. I have personally send data via PSK31 from my house in Va to Australia using 1 Watt of power. That's by no means a km/Watt record. See this database for contacts made.

This guy (who received my 1 Watt signal) is seriously into weak signal work.

While school contacts with the space station are routinely made through the Amateur Radio on the International Space Station program, many of those contacts are made using a traditional ham radio.

They made their own radio that used Amateur Radio frequencies (nitpick: Amateur Satellite Service freqs) as opposed to using a Yaesu or Kenwood radio on Amateur freqs. To hams like me, this isn't a big deal. Designing software-defined radios and protocols that can span Virginia->New Zealand using 1W of power is cool, but making an 5W VHF or UHF radio is so 1970's.

The recent Amateur radio mode called WSPR ('whisper') can work with a signal around 27 dB below the noise (SNR of -27dB). This site records contacts between hams worldwide in real time. Most activity is on 30m.