[AMRadio] Ceramic feedline spacers

[D. Chester]

> I have a bunch of 2" (hole spacing) ceramic feedline spacers, they have a 
> hole in each end with a groove running around the outside, now here's the 
> question,( and I am only asking this as after looking for most of the 
> evening here I cannot find the answer anywhere) Does the feedline wire go 
> in the hole or on the outside and how to fix the wire to the spacer, I 
> would assume the feedline wire goes in the hole and a wire twist holds it 
> there, however, some say the feedline goes on the outside with the wire 
> twist from the inside.
> 73 Max

The feedline wire goes on the outside, resting in the groove at each end of 
the insulator.  The tie-wire (I believe a better term than "twist wire") 
goes through the hole, with several turns at each end of the tie-wire 
wrapped  round the feed line wire.  The tie wire should be wrapped with the 
spiral going in the same direction at each end, so that the two ends will 
come out of the hole and make initial contact with the main wire on opposite 
sides of the main wire.  In other words, the tie-wire should spiral round 
the main wire, go through the hole, and come out of the hole and continue 
spiralling in the same direction, to maintain balanced tension on the main 
wire so that the main  wire won't tend to pull out of the groove. For the 
tie-wire, use solid copper wire a few gauge   sizes smaller than the main 
wire.

Look in an ARRL "Radio Amateur's Handbook" to find a drawing that clearly 
shows how this is done. It was always included in the older handbooks; I am 
not sure if the newer ones have it or not, since I have been surprised at 
some of the most useful topics they have deleted from the newer editions. 
Maybe  that's why they dropped the name "Radio Amateur's Handbook" and now 
simply call it the ARRL Handbook.

I have heard of people running the main wire through the hole, but there are 
two problems with doing it that way. First of all, the hole is only large 
enough to accommodate a wire up to a certain size.  Secondly, if the 
insulator were to break (a common occurrence), how would you ever replace it 
without having to completely disassemble the entire line just to thread the 
new insulator in place? Besides, it would be a tedious process to thread 
each insulator from one end of the feed line all the way along the length to 
the spot where the insulator is to be attached.

I would recommend keeping a handful of extra insulators on hand just in case 
you need to replace broken ones. Every line I have ever built has eventually 
needed replacement of one or more chipped or broken insulators.

The larger dimple-like groove on the flat side of the 2" insulator at each 
end is for copper tubing.  In that case, the tubing would rest in the larger 
groove, and the tie wire would  wrap round the tubing, pass through the 
hole, loop over the tubing, pass back through the groove at the tip-end, and 
continue to the opposite side of the insulator and that end of the tie-wire 
would wrap round the tubing, continuing the spiral in the same direction. 
Copper tubing is for making a lower impedance feed line, usually for a 
Johnson "Q" section.


Don k4kyv


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