This is from K1TTT technical reference. It is what I used for making a coax choke. The larger article elaborates on this and is much more technical but these were his findings in conclusion.
It can be a bugger to wind RG-213 on a 4 inch piece of PVC but it can be done with good plastic cable ties.
Conclusions
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- A 1:1 coaxial balun with excellent choking reactance for 10 through
20 meters can be made by winding 6 turns of RG-213 on inexpensive 4
inch PVC sewer pipe.
- For 40 or 30 meters, use 12 turns of RG-213 on 4 inch PVC sewer
pipe.
- Don't bunch the turns together. Wind them as a single layer on a
form. Bunching the turns kills the choking effect at higher
frequencies.
- Don't use too many turns. For example, the HyGain manuals for my 10
and 15 meter yagis both recommend 12 turns 6 inches in diameter. At
the very least this is about 3 times as much coax as is needed, and
these dimensions actually give less than the desired choking impedance
on 10 and 15 meters.
