[Elecraft] 270 foot (ish) Doublet & K3 ATU

[Peter Torry]

Iain,

It may be worth going back to basics and reading up on doublet antennas 
as well as open wire feeders.  The critical length is half of the top 
plus the feeder length and this should be adjusted so that it isn't 
resonant on any band you wish to use.  This because it is easier to 
match a medium impedance but reactive load rather that a high or low 
impedance load.  The impedance of the feeder is immaterial in this case 
as are issues of balance so erect whatever you can and enjoy using it.  
Based on your dimensions of 270ft top and 33ft feeder the critical 
length will be 168ft which may give trouble on some bands so may I 
suggest using about 148 to 150ft.
Hope your system works out OK

73

Peter

G3SMT