Browsing through the internet the thought struck my mind if there was a method available that can help give a rough idea on the estimated altitude required to achieve a certain distance based on theoretical RF Fresnel zones for both 915 MHZ and 5.8 GHZ frequency that we use for our transmitter and video links.

I found an interesting but yet simple to use website setup by someone called Mr.D : https://www.mrd-rc.com/tutorials-tools-a...alculator/



A useful feature of the web based tool is that it also takes into account any direct obstacles such as trees when providing the optimal altitude required.

The web page does not mention the back end formulas or calculations used else it would be interesting to perhaps setup a lua script on a radio without relying on a webpage. But the webpage scales perfectly on most smart phone screens to be able to punch in the values and get a quick calculation.

I also found an interesting document published by an Australia based entity called Campbell Scientific Australia that has a published document (but please be mindful of copyright information) with most of the theory and formulas related to Line of Sight Obstruction with regards to RF signals : https://s.campbellsci.com/documents/au/t...uction.pdf

Based on the document referenced in my previous post (https://s.campbellsci.com/documents/au/t...uction.pdf) I have put together a quick Excel sheet (attached) working through the various calculations to obtaining optimal model/aircraft height to avoid interference from an obstacle:



To use the sheet we enter the required values in Black/Grey text to get calculated values in Red text.

Basically we keep adjusting the Height of Tx antenna (h2) value and pay attention to the CFFZ result in the last rows of the sheet till the value is positive indicating adequate clearance.

I have contacted the Mr.D who put together the online Simple FPV Antenna LOS Altitude Calculator (https://www.mrd-rc.com/tutorials-tools-a...alculator/) to get an understanding of the calculation used and a quick response from him explained that the calculations used on the webpage are based on basic trigonometric calculations (taking into account Fresnel zone radius and the elevation drop as a result of the curvature of the Earth). I have emailed him my worksheet sharing my findings of calculated/recommended model/aircraft height at a certain distance and how it compares to the value we calculate using the website.