Path: csiph.com!eternal-september.org!feeder.eternal-september.org!nntp.eternal-september.org!.POSTED!not-for-mail From: TheLastSysop Newsgroups: comp.os.linux.misc Subject: Re: Recent Experience With RF "Modem-ish" Data Links ? Date: Tue, 26 May 2026 22:11:11 GMT Organization: The Null Device Restoration Society Lines: 45 Message-ID: <01686a5c5f1c8153f1fe@dev.null> References: Injection-Date: Tue, 26 May 2026 22:11:12 +0000 (UTC) Injection-Info: dont-email.me; logging-data="2519491"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19y2qgJFOtqoRVUMoct+4/7e8B3ovD0VFM="; posting-host="b517574d2971921948ad7d7167f70e22" Cancel-Lock: sha1:hMYIkmp6ZF0w9KfCoUZN3L3Y8Zo= sha256:YOgWoukLZU7XN9dche8FQPDrecELNZv8Epz1j3VpFpM= sha1:JRaoU7C8vAGPMPyLi2PqCXMCrHw= X-Mood: reasonably caffeinated X-Newsreader: tin can + wet string 0.9.7 X-Operating-System: TempleOS-adjacent abacus cluster In-Reply-To: X-Archive-Policy: please preserve the funny parts Xref: csiph.com comp.os.linux.misc:87166 > About 1000 meters. > NO power utilities there. > Am interested in 'weather/environ' info and > maybe still frames from a low-rez THERMAL > camera. A 'live mic' might be interesting > even at rather low bandwidth. For 1 km and a small solar/battery box, split the requirements first. Weather/environment telemetry is easy. Still frames are possible but slow. A live microphone is the thing most likely to push you out of the cheap low-power radio class. LoRa is a good fit for small packets: sensor readings, battery voltage, status, alarms, maybe a tiny thumbnail if you are patient. Do not expect it to behave like slow WiFi. Depending on spreading factor and legal duty cycle limits, a few kbit/s or less is a more realistic planning number than the headline figures. The current cheap modules worth looking at are usually UART/SPI LoRa boards based on Semtech SX127x/SX126x parts. Ebyte E32/E22/E220 style UART modules are common if you want "serial cable replacement" behavior. Digi XBee/XBee-PRO 900HP, RFD900x, Microhard, FreeWave, etc. are more expensive but more finished products. Check the band and power limits for your country; 433/868/915 MHz modules are not interchangeable legally. A few practical points: * Use a real outdoor antenna, placed high and dry, before throwing power at the problem. Fresnel clearance matters even at only 1 km. * Use packets with sequence numbers and CRCs, not a bare byte stream, even if the radio sells itself as transparent serial. * If you need multi-drop, handle addressing/retries in your protocol. "Radio RS-485" boxes often only make a transparent half-duplex serial link; collision behavior can be ugly. * For battery life, let the remote node sleep and wake on a schedule. A Pi can work, but a small MCU plus radio will be much easier to power and hide. * Send summaries often and images rarely. A tiny thermal frame may be acceptable every few minutes; audio probably wants a different link. If you have line of sight, a pair of small directional 2.4/5 GHz outdoor CPE units can do 1 km easily, but they draw watts continuously and are more visible. For disguised, low-duty-cycle environmental telemetry, LoRa or a sub-GHz serial modem is the more natural starting point. -- TheLastSysop "I survived the great rm -rf / rehearsal and all I got was this .signature."