3.5 KiB
| id | title | sidebar_label | slug |
|---|---|---|---|
| aerials | Aerial selection | Aerial selection | /hardware/aerials |
The stock aerials provided bundled with the t-Beam and other boards are, in general a 'mixed bag'. They may not have been selected for your given frequency range, tuned or of a quality design.
Matching an aerial to the frequency of transmission is important, as is choosing an appropriate design.
The aerial's design will affect:
- proportion of the signal which leaves the aerial (efficiency),
- directions in which it's transmitted, and whether it will be affected by horizontal / vertical polarisation,
- proportion of signal which is reflected back within the device itself.
:::caution While the LoRa devices we are using for Meshtastic are relatively low power radios, care should be taken not to operate any radio transmission device without an aerial or with a poorly matched aerial. Un-transmitted radio signal reflected back to the transmitter can damage the device. :::
Important considerations:
- What transmission frequency are you using?
- Devices on another frequency will not be able to interact with yours.
- See this listing by The Things Network for frequencies licensed for specific countries.
- How will you be carrying / transporting the radio?
- A large directional aerial will transmit over significantly greater distance than an omni-directional aerial. However, it must be pointed at its target so isn't optimal for mobile use.
- A tuned half wave whip aerial may have more omni-directional range than the quarter wave stubby; but it will be conspicuous in your pocket.
- Many antennas, especially quater wave stubby antennas, require the use of ground planes to transmit at peak performance.
- Do you want transmission in all directions?
- While humans (mostly water) don't attenuate signal greatly (at LoRa frequencies), buildings & walls do.
- If your aerial is permanently positioned against a building, signal transmitted towards the wall will be largely lost.
- Does my Meshtastic device have the right power range, impedance & connector for the aerial?
- For the LoRa devices it should be 50 Ohm impedance, with SMA connector. Many antennas will be recommended for LoRa use in their technical details.
- By contrast, a close range, contact-less Personal Area Network antenna, or a huge aerial at the end of length of coax designed for a 100W transmitter are not going to be operable.
- Cost, quality and supply service?
- The perfect aerial on paper, sourced from the other side of the world with mixed reviews doesn't compare to a local supplier who has spent time carefully collating all of the aerial data-sheets for comparison and holds stock immediately available - personally I prefer to pay significantly more for a time saving, quality service.
- How close will the antenna be to my Meshtastic device?
- Most cables will significantly degrade the signal strength over any significant distance. It is often more effective to place a node outside, than to have it indoors with the antenna outside.
Terminology / references
You could do a lot worse than reading the Wikipedia entry for Antenna, along with the Wikipedia entry for LoRa.
Instead of listing the terms, let us recommend this superb tutorial by Andreas Speiss (the 'guy with the Swiss accent').