Field Antenna Testing Without Lab Equipment

Professional antenna testing requires a vector network analyzer and anechoic chamber. Field testing with simple tools can still tell you whether an antenna is working as expected for your deployment.

The Two-Node RSSI Test

The most practical field test for comparing antennas:

1. Set up a reference node at a fixed location (indoors at a window, or on a tripod outdoors)
2. Connect your test antenna to the mobile node
3. Walk to a consistent test point 50-200m away
4. Record RSSI (in dBm) displayed in the Meshtastic app on either node
5. Replace antenna with a known reference (stock rubber duck or a calibrated dipole)
6. Return to the same test point and record RSSI again

RSSI difference in dB = antenna gain difference (approximately). A +3 dB improvement means the new antenna has ~3 dB more gain than the reference.

Important: Test at multiple azimuths (compass directions) for directional antennas. Omnidirectional antennas should show similar RSSI regardless of direction.

Checking for Antenna Resonance with an SDR

An RTL-SDR dongle ($25) can help verify antenna resonance:

1. Connect the test antenna to the SDR via an appropriate adapter
2. Open SDR# or GQRX
3. Look at the noise floor across 900-930 MHz while the antenna is connected vs. with a dummy load or no antenna
4. An antenna that's resonant near 915 MHz will show elevated noise pickup compared to a non-resonant antenna at that frequency

This isn't a precision measurement, but it can confirm whether an antenna is "alive" at the target frequency.

Common Field Issues and Quick Diagnosis

Symptom	Likely Cause	Quick Test
RSSI much worse than expected	Wrong frequency antenna, damaged element, or loose connector	Swap with known-good antenna; check connector seating
Range varies wildly with orientation	Antenna is directional (yagi, patch), or near-field coupling to enclosure	Mount antenna away from metal surfaces
Range degrades after outdoor installation	Water ingress into connector or pigtail	Inspect connector for corrosion; re-weatherproof
Node transmits but no one hears it	Open circuit in antenna path (broken cable, wrong adapter)	Check SWR at transmitter; swap cable

Documentation for Installations

For permanent outdoor installations, document your baseline measurements:

• Date of installation
• Antenna model and supplier
• SWR at 915 MHz (from NanoVNA if available)
• RSSI to 2-3 reference nodes at known distances
• Photos of antenna mounting and connector weatherproofing

This documentation makes troubleshooting future performance issues much faster — you have a baseline to compare against.