Total posts : 45366
I’ve recently experimented with loading coils for use with an 8 foot , 1/2 inch diameter copper pipe on a roof mounted mast.
After trying various ferrite core loading coils vs. air core coils, I believe I’m going to settle on a space wound air coil (1/2-1 wire diameter spacing) on a polypropylene jar. Using a field strength meter, the space wound air coil has the edge over the ferrite coils. The range difference of the spaced air coil over a similar tight wound coil on a PVC form is significant. Once the geometry is set, I plan to replace the magnet wire with Litz.
I’ve not seen much discussion anywhere of using Litz for loading coils. But there’s been plenty of experimentation and discussion of Litz coils. In an unloaded coil, properly configured Litz can double or triple the Q over magnet wire. Q around 1500 has recently been achieved for MW frequencies using Litz and ferrite: http://www.midnightscience.com/rapntap/topic.asp?whichpage=8&pagesize=15&forum_title=Crystal+Radio+Think+Tank+%2A%2A+Advanced+Forum&topic_title=Air+coils+enhanced+by+ferrite+%2E&forum_id=10&topic_id=4755
Although the contrawound coil is perfect for my Macrohenrydyne radio described above, at this time, I don’t see much benefit to a contrawound loading coil.