Work in progress. The making of an air wound pi coil!

It has been a while since last post. The build has not stalled but the process has been very slow lately. The reason is that I have had too much work to do the last months. I have not been able to spend any time in the work shop. However, this Easter weekend gave me the opportunity to to do some work. The goal for this weekend was to make the 30 to 80 meter pi coil. The raw material is 3 mm copper wire which should be more than adequate for 1 KW in SSB service. Further on, this size should be able to withstand continuos service as well

The completed coil mesures 70 mm OD, 84 mm in length and has a total number of 18 turns. The measured inductance is 11,18 micro Henry and the calculated value is 12, 54 micro Henry. The needed inductance for the Pi-L tank is 11,04. So the result is perfect!

First step of the coil making. About 40 turns coiled up on a 60 mm steel tube. I used only 18 turns.

Four polycarbonate ribs are cut to size. They will support the coil and keep the pitch of the turns through out the length of the coil. Polycarbonate (Lexan) is a very good plastic materiel, far superior to the more common acrylic. It is a lot easier to work with machine tools since it does not splinter as easy.

The supporting ribs are drilled to accommodate the coil.

This is the time consuming part! The polycarbonate ribs are threaded on the coil, turn by turn!

The coil is ready! Nice and shining. It almost looks factory made.

After making this 11 micro Henry coil I realize that the amplifier housing does not have room to accommodate the 160 meter pi coil nor the L-coil for all bands if I make them as traditional air wound coils. For this I need to investigate how to use toroids in high power coil design!