Recently acquired a JR Receiver R800S (35Mhz) to install in a Kalt Cyclone 1980's heli - the antenna is 83cms but the end looks frayed. What should the correct length be please?

Replace from RX , open and solder in new one . You can range test ,sometimes a little off is no biggie .

I don't know how we made it until 2.4 , well worth the upgrade

I stole it ,flew it and gave it back ;)

Anyone actually have one ?

Should be about 40 inches. In a heli, the antenna is all the hell out of tune anyway. Not critical.