Heat Shrink Your Antenna Coils
In this photo, I am applying heat-shrink to my recently completed 17 meter coil assembly.
Just so you know, not all heat-shrink materials are created equal.
The heat-shrink that I selected for covering this coil assembly is a adhesive lined Polyolefin, with a 4:1 heat shrink ratio.
When heat is applied to the heat-shrink with a heat-gun, the inner hot melt adhesive lining melts, and conforms to the shape of the coil assembly, sealing out the environmental elements that would throw the antenna into tizzies when the weather is a factor, as it quite often is throughout the winter months here in southern Alberta.
If you haven’t used heat-shrink tubing before, don’t be concerned, as it is easily applied. I have several heat guns, one being a heat gun made for this purpose, the second one I own I have had for years, and its original purpose was for applying monokote coverings on RC model airplanes.
Once you slide the shrink tube in place over the coil assembly, start heating the shrink-tube from the center of the coil assembly and working out to the ends. While applying heat, rotate the coil, making sure that the shrink-tubing follows the contours of the coil. Also ensure that you have applied the proper amount of heat, melting the adhesive which will be visible at either end of the shrink-tube. This will seal the coil assembly, keeping the coil dry within and the antenna tuned.
Do not apply more heat than necessary to shrink the tubing, as you do not want to damage the coilform.
Be aware that any dielectric placed over the coil assembly, decreases the Q of the coil, because the dielectric increases shunt capacitance.
So its a trade-off... without the covering, the coil although higher in Q, is vulnerable from the weather....with the covering and some loss of Q, your good to go in all seasons.
Still, for the small loss that the heat-shrink causes to the Q of the coil, the benefits are a antenna that stays tuned when the weather turns nasty.
The coil without its covering...