[TowerTalk] Open Wire Line

[w8ji.tom]

Hi Dave,

>  Since I've tried making my own open wire line and found it very 
> difficult due problems finding spreader material,  can you give any 
> indication how commercially  made ladder(window) line would perform?

Don't know. There are too many types. I measured some ribbon-type "ladder"
line and it was OK but no where near like the real stuff. The thing I don't
like is how much it changes when it gets wet.


I sure wish someone would make some real air insulated line. I'd buy a mile
of it! 

>  What did you use for spreader material ?

Lexan, a uv resistant grad. But I only wound up using one spacer every 15
or 20 feet. I pass the wire through smooth glazed ceramic post insulators
every 100 feet or so, and let it float. Only one end of my lexan spreaders
is anchored to the wire rigidly, the other end captivates the wire but can
still slip.

I pulled the line hard and pre-stretched it. I anchor one end solid, and
tie the wires on the other end  through dead end strain insulators to a
rope that loops over the wheel of a pulley. I pull tension on that pulley
hook, so each wire in the line gets exactly the same tension.

> PS: I've just concluded an independant study of toroid materials and 
> believe that type 43 ferrite would probably make better baluns for 160m 
> than the type 61. 

Maybe, maybe not. Loss tangent is lower in 61 material, so there is
absolutely no heating at all in the cores. If I ran low power, I'd use 73
mix. The higher the power, the lower the loss tangent I use so the material
does not reach curie temperature even though I still use transmission line
type transformers. My choke baluns that couple the 9:1 transformers use 43
material with silver/teflon coax. 

This combo provides 1.1 to 1 SWR on 1.8 MHz, perfect on 10-15 MHz, and only
1.5 to 1 on 35 MHz when terminated in 450 ohms (the line impedance). About
half the .17 dB loss is in the transmission lines, the rest in the cores.
It's certainly the best I can do, but I'd like to have better transformers
if you or anyone can help.

Many people would probably use a good matching transformer that handles
high power and high SWR.

73 Tom

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