dAISy off-grid receiver

Off-grid AIS Station is now live on marinetraffic:
Receiver altitude is approx. 230m ASL, so should be better

Station coverage:
https://www.marinetraffic.com/en/ais/details/stations/910/

Remote unit battery level monitor real-time
https://thingspeak.com/channels/113422
https://io.adafruit.com/steve098/aismon

Compare the receiption to the Moxon square RTL-SDR receiver in my loft at sea level,
https://www.marinetraffic.com/en/ais/details/stations/1618/

The remote receiver picks up vessels in Oban Bay more reliably (not surprising as it can see over the top of several hills compared to my home station), and sees 'around the corner' into the Sound of Mull better, being able to track the Loch Fyne CalMac ferry on most of its route from Lochaline to Fishnish on the Isle of Mull.

It sacrifices coverage up Loch Creran.


Todo:
* convert daisy to 3.3v operation. I have received advice from Adrian Studer on how to fix excess power drain when operating the dAISy at 3.3v by isolating the 3.3v LDO reg.
* convert the AIS parser script that powers the Twitter feeds @ObanAIS and @ObanSARwatch to accept AIS sentences from the remote receiver.