[Neil Purling]

The coil form is 38mm in diameter.
Frequency range for Long Wave is usually 150 - 270 Khz.
Tuning capacitor is 500pf. I have no idea of what it's minimum capacitance is.

There are commercially available coils (just), from Isoplethics, but they have a seperate reaction winding and there's no tap for the detector's cathode.
They do have Octal plug in coil forms, which I would like to use, of the diameter mentioned above.

Is the usage of a ferrite rod aerial going to be necessary?
The only large diameter material I can think of is plastic drain pipe, from out of the nearest skip.