ELRS Redundant Diversity Groundside TX Version

Owned by Ishman Mann
Last updated: 2024-10-27
3 min read

Owner: @Ishman Mann

ToDo:

  • Come up w/key features and Modify the schematic by @Nolan Haines for groundside TX applications

  • Create a corresponding layout

 

 

Table of Contents

 

Background

 

This board will take the best parts of ELRS Gemini TX and ELRS Redundant Diversity RX, and combine them into a groundside TX. Likely this board won’t use Diversity TX (which doesn’t really exist), but Xrossband.

Ideas

 

 

 

Key references:

 

 

 

Needs Assessment

Top goals

  • Current sense on the tx

  • Have 2 Geminis (4 LR221s) on the board for Xrossband. Make it compatible with the RX board.

    • Improve upon the ELRS Gemini TX.

      • Port over existing features and add new ones

      • Design to solve/avoid the issue it was having!

    • Easily programmable

    • Configurable over UART, WIFI, etc…

 

 

 

Constraints

  • Size and weight are not limiting factors

  •  

 

 

 

Architecture

 

  • I probably don’t need the ESP 01F because Xrossband has dual band anyway. But there is a chance I will keep it.

 

 

  • Need to have high output power, eg 1W. (But no off the shelf RX can support over 250mW telem). Need to determine appropriate power arch and if the current LR221s are good enough.

    • → Seems like the current LR221s on the ELRS Redundant Diversity RX has a TX power of 15dBm max for 900 MHz. Is this enough? DEFINITELY NOT, we need something like 27dBm or 30dBm

      image-20241019-013055.png

       

    • ^But what about this high gain antenna thing?? → I believe its more directional than a normal antenna, but its worth looking into

    • Solid option: use an RF amplifier - there are plenty of options and this needs a decision matrix

      •  

  • Carefully draft a power architecture. The one in the diagram below is just rough with not much thought yet. Definitely want good isolation where needed, and need to consider power demand

 

 

  • consider dual passband filter of somekind

    • https://blaauw.engin.umich.edu/wp-content/uploads/sites/342/2017/11/472.pdf

    • If this can somehow be implemented, it would be a lot more cheap than a tunable filter (which I would never add because they’re so niche and expensive)

    • If this can somehow be implemented, it would be a lot more cheap than a tunable filter (which I would never add because they’re so niche and expensive)

 

 

 

 

Test/Validation Plan

 

Layout Considerations