Markus;
But this 4' coil only takes me down from already resonant ant at 69 kHz.  It is in series with those coils shown on shelf at operating position. 
At bottom of this 4' coil is a tap about 6 inches up from bottom to hit 29.5.  With those additional turns I can go down to near 28.000.
All my ant coils are wound with either 12 or 14 wire.  That was available but too large.  I think 18 would be fine.  At 3 amps ant current these coils run cold, barely noticeable above room temp-Bob