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Smart Radio Trouble-Shooting

Guide

Fresnel Zone Clearance

The required Fresnel Zone clearance is the radius around the line-of-sight path which must be

clear of obstancles. The Fresnel Zone clearance is frequency dependent, so we recommend

using an RF calculator to calculate the required clearance for your application. Drone

applications typically do not need to worry about Fresnel Zone clearance, but it is critical for

unmanned ground vehicles (UGV).

Noise and Interference

Background noise and interference has a direct effect on the achievable range. The 2.4-GHz ISM

band may be the most crowded frequency band in the world due to the ubiquity of 2.4-GHz

WiFi. Therefore, the achievable range in urbanized areas is notably poorer for the 2.4-GHz band

than other bands. Aside from the 2.4-GHz band, the 915-MHz band and the 5-GHz bands are

also license-free and may be highly congested depending on where the radios are being

deployed. You can measure the level of the background noise picked up by the radio using the

built-in spectrum analyzer on the wireless configuration page. This is only accessible in the

Advanced Settings. The figure below shows the wireless page with Advanced Settings enabled,

and a Spectrum Scan button available for the radio0 interface. The spectrum scanner is only

available for 10 MHz channel bandwidth or greater.

If you perform a spectrum scan, the radio will scan all channels. We recommend narrowing in

on the desired operating channel to check the noise performance as it will be faster and more

accurate. Note that the thermal noise floor is approximately -116 dBm per FFT bin in a 20-MHz

Fig. 2 – Wireless page with Spectrum Scan available

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September 8, 2021