LoRa Antenna Selection
The stock antennas provided with the T-Beam and other boards usually come from 'mixed bags'. They may not have been designed or tuned for your given frequency range, and they may not be of a quality design.
Matching an antenna to the transceiver frequency is important, as is choosing an appropriate design.
The antenna's design will affect:
- Efficiency - The proportion of the signal which leaves the antenna
- Direction in which the signal is transmitted
- Interference by horizontal or vertical polarization
- Amount of signal which is reflected back to the device itself
While the LoRa devices we use for Meshtastic are relatively low power radios, care should be taken not to operate any radio transmission device without an antenna or with a poorly matched antenna. Un-transmitted radio signal reflected back to the transmitter can damage the device.
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 antenna will transmit over significantly greater distance than an omni-directional antenna. However, it must be pointed at its target - so it is not optimal for mobile use.
A tuned half-wave whip antenna may have more omni-directional range than the quarter wave stubby; but it will be conspicuous in your pocket.
Many antennas, especially quarter 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 antenna is permanently positioned against a building, signal transmitted towards the wall will be largely lost or attenuated.
Does my Meshtastic device have the right power range, impedance, and connector for the antenna?
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.
In contrast, a close range, contact-less Personal Area Network antenna, or a huge antenna 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 antenna 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 antenna 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. The exception might be if there is extreme heat, cold, or humidity, and if the shortest possible low loss cable is used.
Still, a proper enclosure should mitigate bad weather.
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 Spiess (the 'guy with the Swiss accent').