Friday, November 13, 2009
1928 Hartley Coils
Pictured are my 80 and 40 meter tank coils. Ross Hull made a strong point in his QST article that these coils need to be able to handle a lot of current (5 amps of RF for this design), be mechanically stable and tune with as much capacitance as possible.
These coils were wound out of 1/4" OD copper tubing. A piece of 2 3/8" OD pipe was used for a winding form. Once a coil was wound I installed it and then adjusted the turn spacing so that the bottom edge of each band fell close to maximum tank tuning capacity.
While shopping for copper tubing I found that tubing wall thickness varied brand to brand. For best current handling and mechanical stability I bought the heaviest/thickest I could find.