300 ohm ladderline

[Highlander_821]

I built an antenna that is going to use 300 ohm ladderline for a feedline.

Currently, I have about 5 coax feedlines running into the shack through a 3 inch PVC feedthrough. Can I run the ladderline through that short conduit alongside those coax cables? There is plenty of room for it, but will it not like being next to the other cables?

 

[Beetle]

Run it separately, keeping it several times the wire separation distance from other metallic objects, including other wires, coax shields, window sills, etc.

5x the wire separation is a good rule of thumb.

And the "300 ohm ladderline" is probably "twinlead". True ladderline has bare wires (or varnished wires for insulation) running through the spacers, with no overall insulation. It's typically closer to 600 ohms characteristic impedance simply because of the tiny spacing required for anything with much lower impedance.

 

[W5LZ]

Highlander_821,
'Beetle's right, that twin-lead/ladder-line won't 'like' it much. A very simple way to run almost any kind of 'ladder-line' is through a board placed in a window (if you happen to have a window handy). A couple of holes the right distance apart. I just cut a short section of ladder-line (window line, actually, so what) for the feed-through, connected the rest of the line to the outside ends. It will have a sort of impedance 'lump' at the feed through point, but as long as it's only a small 'lump', it doesn't make a lot of difference. ('Small' in this instance means that what the line goes through is non-conductive, sort of 'thin', and doesn't 'deform' the line much.) I've used the same board/window and feed through wires for quite a few years with no problem. I see that 'MFJ' now offers the same sort of thingy commercially. No experience with it so won't say good/bad. I'm too cheap so I made my own.
Just for 'grins', you might try your present 'feed-through' thingy and see what happens. I'd be interested...
- 'Doc

 

[Highlander_821]

It is 300 ohm "window" twin lead, with a .91 VF. I think I'll just make a separate, smaller feedthrough next to the one that I'm using now.