# On the air with RF APRS > For licensed hams, covering how to beacon weather on 144.390 MHz with Direwolf or a hardware TNC, plus antennas, grounding, duty cycle and a solar power budget. Weather stations · How-to guide · https://wxalerts.org/docs/weather-stations/on-the-air/ This page is for licensed amateur radio operators only. If you do not hold a license, you cannot transmit on these frequencies, but you lose nothing: the internet-only CWOP path described in [Getting an ID](/docs/weather-stations/registration/) puts identical data in front of the same forecasters. Putting a station on **144.390 MHz**, the 2 m APRS channel in the US, makes it visible to local hams and to any igate in range even when your internet is down. For a station whose whole purpose is reporting severe weather, that independence is the point. ## The hardware paths **A hardware TNC and a radio.** The Kantronics **KPC-3+** is bulletproof and has a dedicated weather and telemetry mode. Byonics **TinyTrak** and **MicroTrak** are cheaper. **Mobilinkd** TNC3 and TNC4 speak Bluetooth KISS. **A software TNC.** **Direwolf** on a Pi with a cheap USB sound card and any 2 m radio. The most flexible and by far the best documented. **The classic WXNOW.TXT path.** Peet Bros Ultimeter and Davis hardware produce a standardized `wxnow.txt` file that a TNC or Direwolf reads and beacons directly. **All-in-one trackers** that accept a Davis or Peet feed without a computer in between. ## Direwolf as a weather beacon ```bash sudo apt install direwolf ``` A minimal `direwolf.conf` fed from a file: ``` ADEVICE plughw:1,0 # your USB sound card; find it with: aplay -l ACHANNELS 1 CHANNEL 0 MYCALL N0CALL-13 # -13 is the weather station SSID MODEM 1200 # AFSK 1200 baud PTT GPIO 23 # or: PTT /dev/ttyUSB0 RTS or VOX # Weather beacon every 10 minutes, one wide hop, WX symbol, data from a file: PBEACON delay=1 every=10 symbol="weather station" \ lat=33^16.04N long=096^31.96W \ commentcmd="tail -1 /home/pi/wxnow.txt" via=WIDE2-1 ``` Direwolf formats that trailing `wxnow.txt` line into a valid APRS weather report for you. **Test with no transmitter connected first.** Then decode your own output to confirm it is well formed: ```bash echo 'N0CALL-13>APDW17:!3316.04N/09631.96W_120/005g010t021...' | decode_aprs ``` For keying the radio you have three options. **GPIO** is cleanest: a transistor keys the radio's PTT line. **CM108** works with many cheap USB sound fobs, and with DigiRig, AIOC and DRA boards that expose a GPIO for the purpose. **VOX** is a last resort. ## Should it also be an igate? Often, yes. A **receive-only** igate is cheap insurance that local RF traffic reaches APRS-IS at all. ``` IGSERVER noam.aprs2.net IGLOGIN N0CALL 12345 # ham callsign and REAL passcode # no IGTXVIA line = receive-only, which is the safe default ``` A **transmit** igate (`IGTXVIA 0 WIDE1-1` plus a filter) gates internet traffic back onto RF and carries real responsibility: channel congestion, and relaying traffic that should not have been relayed. Run one deliberately, with a tight filter, or not at all. A weather beacon does not need to be one. ## Radios and duty cycle A station beaconing every 5 to 10 minutes keys the transmitter for about a second at a time. Thermally that is nothing, so even a cheap radio survives it. The problem with Baofeng-class handhelds is not heat but spectral purity and frequency stability: they are dirty transmitters. Acceptable for occasional beaconing, poor as a 24/7 igate transmitter. A purpose-built data radio, or a used commercial LMR mobile from Motorola or Kenwood on 144.390, is a much better long-term answer. The power arithmetic is worth internalising: at 5 W transmit, one second in every 300 is about **0.017 W** of average transmit contribution. Receive and idle current, at 50 to 200 mA, dominates your power budget entirely. Do not size a battery around transmit power. ## Antenna, feedline and grounding A simple quarter-wave ground plane or a commercial 2 m vertical at modest height is all this needs. Feedline loss matters more than people expect: at 146 MHz, LMR-400 runs about 1.5 dB per 100 ft against roughly 4.5 dB for RG-58. Use LMR-400 on any long run. Grounding and surge protection are not optional on a station whose job is to report lightning. Bond the mast to a ground rod per **NEC Article 810**, fit an in-line coax gas-discharge arrestor at the entry point bonded to the same ground, and put grounding blocks on data and power lines. A station that reports thunderstorms is by definition installed where lightning happens. ## A solar and battery budget Worked through for a remote site, so you can substitute your own numbers: | | | | --- | --- | | **Load** | Pi Zero 2 W plus SDR/TNC plus radio idle ≈ 4 W continuous → **96 Wh/day** | | **Battery**, 3-day autonomy at 50% depth of discharge | 96 × 3 / 0.5 ≈ 576 Wh → a 12 V 50 Ah LiFePO4 (~640 Wh) fits | | **Panel**, at 4 winter peak-sun-hours | 96 / 4 / 0.7 ≈ 34 W → round up to 50–100 W for margin | | **Controller** | MPPT with the correct LiFePO4 profile | On chemistry: **LiFePO4** is light, cycles deeply and lasts, but **must not be charged below 0 °C**, so use a BMS with a low-temperature cutoff, or a self-heating battery, in a cold climate. **AGM** tolerates cold charging but is heavier and shorter-lived. If the budget is tight, cut duty cycle rather than capacity: deep-sleep the microcontroller between beacons on an ESP32 build, or power the radio only when it is time to transmit. ## Frequencies outside the US | Region | Frequency | | --- | --- | | US and Canada (ITU Region 2) | 144.390 MHz | | Most of Europe (Region 1) | 144.800 MHz | | Australia | 145.175 MHz | | Japan and parts of Asia | 144.640 / 144.660 MHz | Check your national bandplan and licensing before transmitting anywhere. Note that the internet-only path is identical everywhere: non-hams in every country use APRS-IS and never touch RF. ## Next [Install, commission and maintain](/docs/weather-stations/commissioning/) covers mounting, grounding and verification. The [APRS weather packet](/docs/weather-stations/packet-format/) describes the paths and formats this page assumes.