Data Uplink without Internet connection, APRS-RF, 144.390MHZ

Until now the only way to send station data to the world wide web was through an internet connection provided by a WiFi access point.  Not much of a problem as long as the station is near civilization, and even in somewhat remote areas one could get a wifi hotspot provided by a cellular service, however the monthly service charges can add up pretty quick if all you are doing is running a weather station off of it. Then there are the really remote places, where there simply isn’t any reliable cell service …..

Luckily there is a world wide amateur radio network called APRS  (Automated Packet Reporting System) that among other uses provides a means to distribute weather data. The system operates in the 2 meter HAM band,   144.390 Mhz in the US.   Transmission are picked up by repeaters in strategic locations and eventually are relayed to the Internet for world wide dissemination.  The communication technology  is based on analog modems running at 1200 baud. The system is therefore not amazingly fast, but since a weather station also doesn’t have much to report it is an excellent fit. Being a non commercial solution there is no monthly service cost associated, all you need is the hardware and a HAM license to operate the transmitter.  The license required is the entry level license and is terribly easy to obtain.  The local HAM club probably has a Saturday class where you go in the morning and walk out in the evening with license in hand. ( Actually you have to wait for l the FAA to post your station ID ).

The uploaded data can be observed on one of the APRS internet sites, for example The site provides charts and tables , quite possibly in a better format than WU.

APRS Weather Station using Baofeng model UV5R VHF transciver on 144.290 Mhz for uplink.

APRS Weather Station using HAM radio link

To get on the air you will need a handheld  2M HAM transceiver.  I  bough a cheap handheld by Baofeng (UV5RV2+). They run about $30 and are the size of a family radio Walky-Talky.  It’s quite a rugged design and for the price I could not help myself and had to buy two.

The radio needs to be programmed to the correct frequency, the modem and weather station then does the rest.  An external antenna will come in handy to make the most out of the 5 watt transmitter.

To interface between the WX station and the radio I designed a little modem board (Nano Modem) with the help of Mark Qvist who did the initial schematic and firmware (see MicroAPRS )

Tiny modem board that interfaces between Weather Station and HAM radio to communicate on the APRS network.

APRS Nano Modem interface adapter

The station, modem and radio are wired together at the moment, 3 wires from Station to modem, and  4 from modem to the radio plugs.  If there is a demand, one could make a daughter board that directly plugs onto the station main board to simplify installation.

The station firmware got an upgrade to include the APRS-RF upload option. All that’s needed  is to set the station ID to the operators HAM station identifier and correctly set the long/lat coordinates. The station can report wind,rain,temp, humidity and barometer.

I did some power consumption measurements on the station and modem board.  Since a WiFi connection is not needed in RF mode, the station firmware turns the WiFi module off when not in use. This  significantly reduces the power requirement from 150 ma down to 45ma with passive wind instruments, or 80ma with the active, high resolution sensors.  This is a total of either 0.2 or 0.4 watt total consumption.  — A  small solar setup should be able to handle.

Next up is to build a solar operated station and put it up on a mountain top away from all civilization to see it run in the wild!




One thought on “Data Uplink without Internet connection, APRS-RF, 144.390MHZ

  1. Very cool, Gary. I ordered the radio today. What about the modem? My very old FT23r that I bought in Hong Kong in 1987 took a dump last year when the battery pack out gassed and pretty much ruined all the electronics above the pack. So this will be neat.


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