Questions about Ladder Line ?...

What 'size' doesn't make a huge difference. I would recommend NOT using 300 ohm TV twinlead though. From there it's a matter of how much you want to spend. The stuff that uses 14 ga. wire is nice and should be strong enough for about anything. The common 'ladder line', 18 ga. solid wire has worked for me for a lot of years though and is cheaper. You can also make your own if you want. Just takes a lot of wire (of whatever size) and some insulators to keep those wires separated.
Typically, having a tuner makes it much easier to live with. If the SWR changes for some reason just retune that tuner a bit and it's taken care of. If you don't want or can't use a tuner then a balun to change the normal 50 ohm coax to a balanced 450 ohms, or 600 ohms, or whatever the impedance of that 'ladder line' is would be needed at both the transmitter end and the antenna end.
I read your description of that 'track line' and the coil of coax, etc, and didn't really understand all of it. So can't relate what I'm talking about to what you were describing. My use of ladder line and tuners goes back quite a ways and I can say it does work. There are some differences in what you/I were/are doing though. I used one antenna on several bands, not an Imax 2000. That Imax has a dedicated tuned circuit at it's input which really does limit it's use to one band. Sure, it can be used on more than one band but that input circuit's 'tuning' goes out the window when you do that, it won't be 'right'. For the use I was putting that ladder line and tuner, I just didn't care what the 'match' was at the antenna's input, it didn't matter much because the ladder line and tuner could handle it. Because you are using that antenna I would definitely try to get the SWR as 'right' as I could with a couple of baluns.
Using ladder line isn't a 'set it and forget it' thingy. Rain, snow, whatever, can change it's impedance. Another good reason to have a tuner. With snow, if you can knock it off of the ladder line, things go back to what it was. Knocking the snow off of 500 some odd feet of ladder line just isn't too practical though. Ladder line and coax are different so you have to treat them differently. It's really not that difficult, but it isn't the same. Using ladder line isn't to everyone's taste, so if you aren't willing to learn the 'do's and 'don'ts', then don't use it. For the distance you have to go to that antenna there would be advantages though. You decide if those 'advantages' are worth the effort.
- 'Doc

A balun in this sort of instance does two things, it changes 'state' from a balanced state to an unbalanced state, and it can transform impedance. Coax is an 'unbalanced' feed line, ladder line is a balanced feed line, it deals with how the things are constructed. Two parallel wires the same length are in a 'balanced' state, equal currents flowing in both of them so that it doesn't radiate (significantly, anyway). Coax is in an unbalanced state because one conductor is inside the other and the currents flowing in one are never exactly the same as in the other conductor (all coax radiates to some slight extent).
Baluns are generally built just like a transformer, a couple of coils. Because those coils are not exactly the same in all cases it can transform impedance just like an AC transformer can transform 120 volts to some other voltage, like 12vac or 1200vac. So, if there's a fairly large difference in impedance, 50 ohms versus 450 ohms, selecting the right 'size' of balun can do that changing from one to the other. That also means that baluns are somewhat 'directional', you don't wanna get'em backwards. That comes in mainly with the connectors used on a particular balun. Two baluns with an SO-239 on one end and two post connectors on the other, with a 9:1 turns ratio (50 ->450 ohms), should work just fine.
That's a very 'general' description of what would happen, it's not 'exact' by any means. It's 'close enough' to understand what's happening though.
"----A========B----"
Point 'A' is a balun going from 50->450 ohms. Point 'B' is another balun of the same size/construction going from 450->50 ohms. The '-' is coax, the '=' is ladder line.

And since that Imax uses the feed line for it's "ground" (or other half), I think I'd use something like a 1/2 wave of coax between it and the balun on that end. That coax ought'a be sort of straight too, but as long as it isn't in a coil it should work.
Confused yet? Oh well, it is confusing. But it works.
- 'Doc

Doc
If a half wave of coax is used to serve as a counter poise, would one of those shunts to ground be useful at the ladderline/coax connection?

Ladder line can not be near or touching anything. Should be suspended in free space. Stick with coax, it will be much better in your case.

kor b,
Don't take that 1/2 w length of coax as 'gospel', I'm guessing at the length actually required. I figure that length should 'cover' what's really required, but I'm not sure of that. I don't understand what you want to do with that 1/2w stub so can't say if it would be of any benefit or not. Sorry 'bout that.
- 'Doc


================

packrat,
You're right, ladder line shouldn't be 'near' or touch things but that 'near' is something like 2 to 4 times the ladder line's width. Figure about 1 inch for it's width and if it's 3 - 4 inches away from stuff it shouldn't be affected significantly.
There are some 'tricks' that can minimize how much ladder line is affected by near thingys. One of those 'tricks' is to twist that ladder line so that both 'sides' of it are about the same distance from that thingy. That means that both conductors are affected -about- the same amount so that it sort of cancels out, mostly. None of this is 'exact' by any means. Typical 450 ohm ladder line really isn't 450 ohms, more like 350 - 425 as a guess. Depends on the dielectric material used to keep those conductors spaced right. If it get's wet then it's impedance changes again. See how that's going? It's mostly a 'ball-park'ish thing. SWR just isn't all that critical so it isn't as big'a 'biggy' as it may seem.
- 'Doc

that coil you talk about in the past was probably a type of balun. and if the distance is as far as you say ladder line will have a lot less loss than coax. 73s midnight special

If Oatmeal wants to utilize ladder line, why can't he simply determine the e1/2ƛ of the ladder line and cut exact multiples of that from the antenna to the station, tune his antenna and get on the air? Would not the radio see the impedance of the antenna and put out maximum power?
If not, what's wrong with simply adding a 9:1 balun at each end of the line, the 9 value ends of the baluns toward the ladder line, the 1 value ends toward the 50 Ohm equipment, and get on the air?

e1/2ƛ = electrical half wave

No reason at all except he'd still have to contend with the balanced to unbalanced thingy on each end. They won't 'cancel out'.
- 'Doc

HomerBB said:

If Oatmeal wants to utilize ladder line, why can't he simply determine the e1/2ƛ of the ladder line and cut exact multiples of that from the antenna to the station, tune his antenna and get on the air? Would not the radio see the impedance of the antenna and put out maximum power?
If not, what's wrong with simply adding a 9:1 balun at each end of the line, the 9 value ends of the baluns toward the ladder line, the 1 value ends toward the 50 Ohm equipment, and get on the air?

e1/2ƛ = electrical half wave

Click to expand...

Yes.
Cut it to electrically corrected 1/2 wave lengths and take the loss in the ladder line. (could very well be less than the matched loss of anything but the very best coaxial cable)
And yes to the 9:1 balun.

But I have come up with something else that is entirely practical and feasible.
I had already posted this in another thread that this author started.
But it lookes like the thread was abandoned.
I will repost it here.

--------------------------------------------------------------------------
The following is one easy and cheap way to implement parallel transmission line for a 50 ohm antenna and transmitter:

Two paralleled quarter wave sections of 300 ohm tv wire on each end of the 450 ohm long run.

square root (450 x 50) = 150
Easy peasy.
Some form of balun will be desired.
Could be simple and inexpensive coaxial choke balun with enough length of coax to wind the balun and to get to the radio/antenna.
The most loss will be the loss associated with the mismatched 300 ohm quarter wave section; (loss associated with a 6:1 mismatch in 7.5 feet of tv twinlead x4) And without doing the math I am gonna say that it can probably be ignored condsidering the lack of loss in the long run of 450 ohm parallel transmision run versus coax will more than make up for it, versus the loss that you would incur in your typical 'good' quality coax.

Here is a link to a pdf about home-made parallel transmission line that you might be interested in reading.