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118 lines
5.7 KiB
HTML
118 lines
5.7 KiB
HTML
<!doctype html>
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<html>
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<head>
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<title>meshtastic radio</title>
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<style>
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body { color: #303030; font-family: sans-serif; font-size: medium; width: 500px; margin: 30px 20px; }
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a:link, a:visited { text-decoration: none; color: blue; }
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a:hover { text-decoration: underline; }
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</style>
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</head>
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<body>
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<h2>Simple Meshtastic Radio</h2>
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<p>
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My take on a home made solution for an affordable, reliable radio:
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<br>(no superfluous parts - very low energy consumption)
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</p>
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<img src="img/radio.jpg" height=250>
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<img src="img/radio-bag.jpg" height=250>
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<br><small><i>open radio / inside a camera bag</i></small>
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<ul>
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<li>WisBlock Meshtastic <a href="https://store.rakwireless.com/products/wisblock-meshtastic-starter-kit" target="_blank">Starter Kit</a>: no display (not needed), no GPS (taken from phone), very low energy consumption
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<li>cheap enclosure 100 x 60 x 25 mm for electronics (no screws)
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<li>3.7V 18650 rechargeable battery + battery holder
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<li>toggle switch (no standby consumption)
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<li>antenna (bendable 90°) either 868 MHz (Europe) or 915 MHz (USA) + pigtail (IPEX-SMA)
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</ul>
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<p><small><i>Make sure both antenna and pigtail match, so they must be both <b>SMA</b>, or alternatively both <b>RP-SMA</b></i>.</small></p>
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<p>All parts above combined cost me around 50€.</p>
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<p>I used a soldering iron, a hot glue gun, a step drill bit, double sided tape.</p>
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<br>
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<h2>Antennas</h2>
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<p>
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<i><small>Important: never power on your radio without a mounted antenna, this can destroy your hardware (power is reflected back to the radio).</small></i>
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</p>
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<p>
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A good antenna is crucial for the radio to function properly.
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</p>
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<p>
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A <a href="https://nanovna.com/" target="_blank">NanoVNA</a> is very helpful to test if an antenna is resonant at the specified frequency (otherwise it's useless).
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<br>The <i>Return Loss</i> should be >= 10dB at the used frequency, which means that at least 90% of the power is going out of the antenna, and only 10% is reflected back to the radio.
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</p>
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<pre><small><b> RL back out VSWR</b>
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---------------------------
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0 dB 100% 0% infinity
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1 dB 80% 20% 17
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2 dB 63% 37% 9
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3 dB 50% 50% 6
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5 dB 32% 68% 3.5
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6 dB 25% 75% 3
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8 dB 16% 84% 2.3
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10 dB 10% 90% 2
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15 dB 3% 97% 1.4
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20 dB 1% 99% 1.2
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<b>RL</b> ..... Return Loss
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<b>back</b> ... reflected back to radio
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<b>out</b> .... going out of antenna
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<b>VSWR</b> ... Voltage Standing Wave Ratio</small></pre>
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<p>
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You can find good NanoVNA clones for about 50€/$ (beware of really cheap/bad clones).
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</p>
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<img src="img/RL.png" width=200>
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<p>
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The screenshot shows a very good <i>Return Loss</i> of 22dB.
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</p>
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<p>
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The antenna needs to be in vertical position while testing, so it's best practice to build a little stand for it, so one can test without touching the circuit, which would inevitably falsify the measurements.
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</p>
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<p>
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It's highly recommended to only trust specialized shops (Mouser, Rokland, RAK store) for antennas, because there is simply too much mass produced garbage out there (talking from experience).
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</p>
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<p>
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Here you can see the inside of one good example, and the worst offender so far:
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</p>
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<img src="img/good-antenna.jpg" height=220>
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<img src="img/worst-antenna.jpg" height=220>
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<p>
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Here an example of a classical (home made) ground plane antenna, using an SMA socket and 2 mm copper wire, after calculating the lengths <a href="https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/" target="_blank">here</a>:
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<p>
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<img src="img/ground-plane.jpg" height=220>
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<p><small><i>Can easily be trimmed by making the vertical wire a little too long, and cutting off one mm after another until it matches perfectly, while having it attached to a NanoVNA.</i></small></p>
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<br>
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<h2>Line of Sight</h2>
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To easily find out if two places are within line of sight, you can use this
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<br><br><a href="http://heywhatsthat.com/profiler.html" target="_blank">Path Profiler</a>
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<p>
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<img src="img/line-of-sight.png" width=400>
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<br>line of sight
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</p>
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<p>
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<img src="img/no-line-of-sight.png" width=400>
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<br>no line of sight
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</p>
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<br>
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<h2>Waterproof Solar Panel Radio</h2>
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<img src="img/solar-radio-1.jpg" height=210>
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<img src="img/solar-radio-2.jpg" height=210>
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<p>
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The RAK store has this nice <a href="https://store.rakwireless.com/products/unify-enclosure-ip65-100x75x38-solar?variant=42490657439942" target="_blank">enclosure</a> where there is enough space for both a 18650 battery and a RAK <a href="https://store.rakwireless.com/products/wisblock-base-board-rak19003" target="_blank">19003 Mini Board</a>.
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</p>
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<p><small><i>The above combination is not supported by the mounting kit, so this is just a personal hack, as you can see if you zoom in on the details.</i></small></p>
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<br>
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<h2>Simple Standalone Device</h2>
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<img src="img/chatter.jpg" width=280>
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<p>
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Support for Meshtastic is increasing continuously. These are <i>CircuitMess Chatter 2.0</i> devices (they come in pairs). I found them on US amazon, also available on ebay.
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</p>
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<p>
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They have some limitations: they only support <i>MediumSlow</i> instead of <i>LongFast</i>, and have a lousy antenna, but work great if those limitations are acceptable for one's use case.
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</p>
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<p><small><i>If you're a hacker you can replace the radio chip with a cheap Heltec RA-62 to support LongFast, and mount a decent antenna.</i></small></p>
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</p>
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<br>
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</body>
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</html>
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