Methodology for Measuring and Comparing the Gain of Tested Antennas (at Home on Your Knee)
As I mentioned in the introduction, I did not use any professional equipment. I prepared everything necessary for the comparison myself, and you can set it up at home. Despite the lack of specialized tools, the results of these experiments still hold informative value for Meshtastic users.
Your Meshtastic device continuously monitors signal quality when communicating with neighboring nodes. These values can be found in the list of neighboring nodes (NodeDB). This means you can determine the received signal level sent by your device from neighboring nodes (this only makes sense for direct connections). By connecting a better antenna, you can indirectly assess how much the reception on the other side improves or worsens after updating NodeDB (note that updating NodeDB can take hours and is not instantaneous). Once you obtain new signal quality data, the difference in antenna gain (in dBi) should approximately match the detected difference in RSSI level on the other side.
WARNING: I probably wouldn’t want to defend this methodology in front of experts who specialize in antennas. It would certainly be criticized. However, I am sharing it because it helped me understand antennas during the initial phase of solving signal quality issues and guided me in selecting the right antenna based on real-world values. This approach can help you as well, requiring minimal resources and no expensive equipment.
Initially, I determined the signal level using NodeDB information for individual nodes, but this was tedious. Instead, I switched to using the “Ping” service, which was initially provided by knowledgeable users on their nodes in my vicinity. This method was faster and more convenient. Later, I managed to implement something similar directly in the firmware (see “Compiling Your Own Firmware”). With some skill and patience, you can modify the firmware yourself and install it on a “remote side” device (left on a windowsill at home).
From a different location, even from a distant hill, you can then “ping” home from any device and immediately determine the signal strength at home—essentially checking the signal coming from your current position. This allows you to assess whether there is good, poor, or no signal at your current location.
If this service gains popularity, you may also “ping” other users’ devices, assuming they don’t mind sharing their airtime. 🙂
Transmitting Power
In the EU, the maximum allowed transmission power for Meshtastic at 868 MHz (specifically, within the 869.400–869.650 MHz band, centered at 869.525 MHz, with a bandwidth of 250 kHz) is +27 dBm ERP (Effective Radiated Power). In this mode, transmission is limited to a maximum of 10% of the time. The ISM band is broader, and Meshtastic can operate at other frequencies, but all relevant conditions must be met (e.g., outside this band, reduced permitted transmission time, power, etc.).
Increasing transmission power extends connection distances, but in real-world usage, it’s better to find the optimal value from below—achieving reliable connections at the lowest necessary TX level. Increasing power beyond this point does not improve reliability; in fact, it can worsen network performance. High transmission power can cause collisions with other nodes, disrupting traffic even beyond your intended range. Similarly, distant nodes using excessive power can interfere with local traffic.
A crucial consideration is that combining a high-gain antenna with maximum TX power may exceed the +27 dBm ERP limit, violating ISM band regulations.
To illustrate:
- A half-wave dipole antenna transmits power (ERP) in all directions.
- The allowed +27 dBm ERP corresponds to 0.502 W radiated omnidirectionally.
- With a directional antenna, this power is concentrated into the main radiation lobe, increasing electromagnetic field intensity in that direction.
- This can lead to exceeding the permitted transmission power in a given direction, violating frequency regulations.
For example, an ERP of +27 dBm is reached with:
- TX set to 21 dBm, plus a 6 dBi gain antenna (21 dBm + 6 dBi = 27 dBm ERP).
How to handle this?
Full transmission power is not always necessary. If your network is stable and range is sufficient, reducing TX power improves efficiency (lower power consumption, less interference). The higher the antenna gain, the more directional it is, meaning it transmits and receives signals from a specific direction only. High-gain antennas are useful for long-range links but can limit reception of nearby nodes outside their radiation lobe.
Optimal transmission power and antenna gain depend on the environment:
- Urban areas: Omnidirectional coverage is preferable for mesh networks over narrow beams.
- Omnidirectional coverage: Use vertical antennas with lower gain (e.g., 3–6 dBi) and adjust power for optimal reliability.
- Directional links: Directional antennas increase range and reduce interference from unwanted directions, improving signal quality.
- Long-distance point-to-point links: Use Yagi or other directional antennas, but be mindful of exceeding ERP limits if TX is set too high.
Golden Rule: Optimize network performance with the lowest possible TX power while maintaining reliable connections to at least three permanently reachable nodes. Less is more in this case.
Transmission Power Control – TX Parameter
- The maximum TX power can be adjusted using the LoRa TX parameter.
- The maximum allowable setting is +27 dBm.
- Many Meshtastic devices only support +21 dBm (e.g., SX1260-based modules).
- If using a device with +21 dBm TX and an antenna with more than 6 dBi gain, be careful not to exceed ERP limits!
Measuring Gain Using PING
As a reference antenna, I used the standard “stick” antenna typically packaged with Meshtastic devices. According to documentation, this antenna has a gain of +2 dBi.
To determine the gain of a new, unknown antenna, I followed a consistent process:
- The Ping service was available on my main node (Brno-LF, ZR10).
- I performed at least 10 signal level measurements at distances of 50–700 m using the reference antenna.
- Immediately afterward, I repeated the test at the same location with the unknown antenna.
- The difference in averaged signal levels provided an estimated gain value.
Example:
- Reference antenna (“stick”): Average RSSI = -48 dBm
- Unknown antenna: Average RSSI = -43 dBm
- Estimated gain: +7 dBi (2 dBi reference gain + 5 dBi improvement)
It might seem simplistic, but the data is provided directly by LoRa’s radio module—what it “sees” is what we get. No theoretical calculations can override real-world measurements.
This method has never failed me. Its usefulness is confirmed by observing similar differences when adjusting transmitter output power:
- Reducing TX from 21 dBm to 6 dBm results in a ~15 dBm drop in received RSSI.
Final Notes on Measurement Results
I emphasize that these are informative values, not laboratory-certified results. However, my experimentally determined values have often exceeded catalog data.
Of all the antennas I tested, I kept and actively use only a few. Below, I provide both catalog gain values and my estimated values based on comparative measurements against the reference 2 dBi “stick” antenna.
Measurements were conducted across a valley, at approximately 700 m with direct line of sight (in conditions resembling motorbike wind speeds—anything not taped down tended to fly away!).
Leave a Reply