As promised above I will now add a few more details to the construction of my 80m coils.
There are many articles written about the construction of loading coils. Many ended by saying that even after doing calculations the best approach was to actually make the coil.
The coils have been wound on 36mm diameter waste pipe..it's what I had lying around..length 90mm (trimmed to this size after tuning). There are 60 turns of wire on each coil (all depends on diam of tube etc.). As I had a roll of the yellow lightweight antenna wire from Sotabeams I used that for the coils.
The only calculations that I made was to measure the 40m element of my 3 band linked dipole (20/40/60) then work out how much extra wire I would need to make it into an 80m dipole. I added an extra 500mm to the resultant measurement. It is essential you make the two coils exactly the same. To calculate how long the tube needed to be I wound the wire around a long length of tube then trimmed the tube accordingly. With suitable wire retaining holes drilled in both tubes I then proceeded to coil it around the tube.
Mounting these coils to the 40m and 60m croc clips I trimmed the wire on both coils by exactly the same amount to resonate around 3.760 (WAB net). I used my Antenna Analyser to take readings. There was a lot of trimming of wire and testing and a few prototypes
I used clear heat shrink sleeve to hold the coils in place and liquid tape over the joints. The coils give me about 25 Khz each side of the net frequency without the need of an ATU. Initial test early in the year have been have been good. All this was done to get on 80m and to keep the antenna compact.
Suitable holes drilled for the wire at both ends of the tubes
Finished coils with liquid tape
Fitted between 40 and 60m croc clips
My blog reports and contact details of activations that included 80m below.
Anyway, cheap to make and fun to experiment with
Hope this helps
73 Allan GW4VPX