Please suggest us method for extending the length of the Coaxial Cable from receiver to antenna as shown in the figure .Actually we need the two antennas to be connected around 700 mm from receiver via the co-axial cable of same specification as shown in the figure (i.e Frsky X8R Receiver).
Frsky used to sell replacement antennas, not sure though if they have the length you need…
Try contacting them.
Or you can make your own with some info from here: https://oscarliang.com/repair-2-4ghz-antenna-rx/
rather than extend the antenna can you use a pair of R-XSR receivers or one of them and an rx8r? That way you can mount the receiver way out on a limb and run the cables back to the center.
Added benefit of redundancy
If you are okay with soldering, should you try to desolder the cable and buy the RF113 for extending. I have one with ACCESS version but it is not available to check at the moment, will do it later and keep you posted.