Good advice on G3TXQ,- Steve's work is my bible for chokes, Steve was a great researcher and an equally great teacher.; explaining complex concepts whilst avoiding the esoteric jargon !
The antenna seems to receive as well, maybe even better, than my earthed, choked Miniwhip on HF and it does an excellent job on VHF and UHF.
RFI... same here with this shack, it's full of computers, monitors, sat TV, quad HiFi, battery chargers and desulphators (the list of gubbins goes on) LOADS of switch-mode PSUs generating a tsunami of noise, Even short 12v DC cables from my main clean PSU collect rf trash on their way to units! I tried using earthed and shielded cable to those devices with no success but I luckily found a bargain bunch of small mains-filters which do an excellent job of cleaning rf off those shack DC cables.... but the real solution of course is for me to kill the sources of the noise. Wiring new power cables to 12v devices from my clean PSU and finding old linear PSUs or even batteries at the other required voltages, will probably be cheaper than getting another mortgage to buy the mountain of ferrite this place needs!
I'll experiment with your helpful suggestions,
73 Jeff 2E0CIT