through the wall with ladder line---

[Catbrain]

I am planning on doing home made ladder line (4 inch). It will of coarse- have to come through the wall at some point.
I was thinking of taking some brass 1/8 rod- cutting it to stick out about an inch on each side of the wall--- thread the ends for nuts. Maybe slip polyethylene tubing over the rods and then maybe some rubber vacuum line over that . Then a bit of caulk on both sides - and maybe a plastic box over the outside. does that sound like it would work ? Im trying to avoid using coax through the wall. how does one terminate ladder line if it runs to the back of the radio or wattmeter or whatever the first piece of equipment is ? Is there no other way than transitioning to coax ?

 

[Catbrain]

Considering home made ladder line (4 inch) with pex spreaders. Thinking about how to come through wall to inside of house.
thinking of using 1/8 brass rods - threaded on each end for nuts-- slip polyethylene tubing over them-- then something like automotive vacuum hose. then insert that through the wall and seal with silicone. Maybe a plastic box on the outside to keep the birds off it. Does that sound reasonable ? want something that wont freak out the impedance of the line.

And--- if i have ladder line all the way to the back of the first electronics (wattmeter or matcher)--- how do I transition from ladder line to screw-on connector ? IS that where I have to hold my nose and use a short piece of coax ?

Tim

 

[prcguy]

Considering home made ladder line (4 inch) with pex spreaders. Thinking about how to come through wall to inside of house.
thinking of using 1/8 brass rods - threaded on each end for nuts-- slip polyethylene tubing over them-- then something like automotive vacuum hose. then insert that through the wall and seal with silicone. Maybe a plastic box on the outside to keep the birds off it. Does that sound reasonable ? want something that wont freak out the impedance of the line.

And--- if i have ladder line all the way to the back of the first electronics (wattmeter or matcher)--- how do I transition from ladder line to screw-on connector ? IS that where I have to hold my nose and use a short piece of coax ?

Tim

Ideally you use a balanced tuner and the ladder line connects directly to the tuner at the radio end. You can't run balanced line directly to unbalanced coax, it will unbalance the system and cause all kinds of problems. Depending on the type of antenna you can either use a balun/matching transformer at each end to go from 50 ohms to probably 600 ohms for your 4" spaced ladder line then a transformer at the other end to get back to unbalanced 50 ohms. If the antenna is a doublet or dipole you just feed the dipole with the ladder line use a good 1:1 choke balun at the radio end.

Some people think you need a 4:1 or 9:1 balun transformer at the radio end when feeding a dipole to match the 50 ohm radio side to the 450 or 600 ohm balanced line, but when directly feeding a dipole at the far end the ladder line becomes part of the antenna and can be almost any impedance at any given point along its length due to interaction with the antenna, so a 1:1 is usually best in that case.

For some installations people have had good success running a wide range coax tuner at the radio then a very short run of low loss coax like LMR400 to get from the tuner to the outside, then the 1:1 balun/transformer outside to the ladder line. Its much easier to get coax through the wall than ladder line and the extra loss of maybe 6ft of LMR400 is usually not a problem. The reason for LMR400 is when coax is operating under very high VSWR, which it will when connected to a ladder line system with balun, it can incur waaay more loss than advertised, plus voltages can be very high if the end of the coax is at very high impedance. A short run of LMR400 will usually overcome these problems good enough.

 

[prcguy]

Thinking about this more, if I were to use 600 ohm balanced line and transition to coax at the building, I would shop for a wide range 1:1 choke balun for the outside using a toroid core with bifilar windings and wide spacing between the wires around the core and preferably Teflon sleeving over the wires for surviving very high voltage. Or one wound with Teflon coax. Then a second 1:1 choke balun just inside the wall and the best I have found is the MyAntennas CMC-130-3K here CMC-130-3K 1-30MHz – MyAntennas.com

For the outside balun I would consider this one: CMC-330-5K – MyAntennas.com

The CMC-130-3K by itself will certainly force a balance between the ladder line and coax but internally it has Teflon coax smaller than RG-58 and I would be concerned with arc over at full legal limit. The CMC-330-5K is less effective but looks like it will handle more HV at the ladder line/coax junction and the CMC-130-3K after it will mop up anything left.

 

[Catbrain]

thank you PRC---- Your first reply- I had read some of that --- but the 2-nd reply is golden nuggets of experience ! I have been reading up in feed lines and mostly what I have found out is that I really didn't understand how feed lines work as far as currents, voltages and impedances.

My limited understanding of where junctions between different feed lines meet-- is that you need a transformer
where the primary and secondary that match each side of the lines. and then the energy does not reflect away at the the discontinuity.

is my understanding if the term "balanced" refer to the ladder line is symmetrical in that both legs are electrically
symmetrical and interchangeable--- where as coax has an form factor where the core and braid look different to the RF and have unequal transmission properties. Is that much sort of correct ? So if the baluns are just impedance transformers i would expect one between coax and any non-50 ohm antenna. and if your radio gear is set up for 50 ohm- then one there if using ladder line. Is the difference between the balun and the unun just in the turns ratio and hence the impedance ratio ? or --in a balun using coax on one side--- is it wound to treat the braid side with a different number of turns than the core side? (as opposed to using ladder line where the 2 legs might have matching windings for each leg on the ladder line half...)

Will the ARRL antenna book teach me about this -- or do you have another better book you recommend for beginners ?

Thanks for the info---- I will go look up that equipment you suggested.

(would I assume you are a Viet Nam Veteran who humped a PRC25 through the jungle ? )
Had a friend in the 101-st that did that. Cant believe how much that thing weighed. :-(
i would have preferred the m-60.