Don't be afraid of ladderline

[Uncle Ronnie 336]

got rid of the 150' run of rg8x into the big pine tree but instead of dropping an arm and a leg on lmr600, i decided to give a folded dipole and 450ohm windowline a try. running a 9:1 3kw balun right behind the radio room. dropping the feed loss from 42% to 5% is HUGE. so no more coax outside! hangs vertical in a big 80' pine and i had to whip the feed over a branch to keep it 90deg from the antenna

 

[SuperLid]

got rid of the 150' run of rg8x into the big pine tree but instead of dropping an arm and a leg on lmr600, i decided to give a folded dipole and 450ohm windowline a try. running a 9:1 3kw balun right behind the radio room. dropping the feed loss from 42% to 5% is HUGE. so no more coax outside! hangs vertical in a big 80' pine and i had to whip the feed over a branch to keep it 90deg from the antenna

Why 9:1?

 

[TM86]

Why 9:1?

Radio wants 50 ohms. Feedline is 450 ohms, or 9 times the impedance.

 

[GlocknSpiel]

Back in the 90's, I ran some 75 ohm hardline that the local cable company took to the scrap yard. I paid $20 for 200 ft of the stuff. I made "transformers" outta 5/8" hard copper water pipe with an SO-239 soldered on the end for each end. These were adjustable by simply loosening the hose clamp and sliding then in or out like a gama match, then tightening them back down. They went from roughly 100 to 30 Ohm impedance. Some of that hardline is still out in the lot next to mine with trees growing on top of them..
There should be one of the copper 'transformers' out there somewhere too.

 

[SuperLid]

Radio wants 50 ohms. Feedline is 450 ohms, or 9 times the impedance.

What is the antenna feedpoint impedance? That theory works only if you are imposing a 450 Ohm constant at the feedpoint.

 

[The DB]

What is the antenna feedpoint impedance? That theory works only if you are imposing a 450 Ohm constant at the feedpoint.

According to This coax loss calculator, a 150 foot run of RG8x with a 1:1 match on the antenna end, 100 watts in will get you 58.498 watts absorbed by the antenna. There is 2.32 dB of loss, all of it from the initial pass through the coax.

According to the same calculator, a 150 foot run of 450 ohm window line (which many now days is mistakenly called ladder line) into a 9:1 match (50 ohm load) on the antenna end, 100 watts in will get you 81.077 watts absorbed by the antenna. Here there is 0.911 dB of total loss, 0.221 of which is from the run through the feed line, and 0.69 is losses from the reflected power as it travels through said feed line.

That is where the op made a mistake in numbers, you can't assume the match for both feed lines of different impedances to the same load will be the same. Of course, assuming the load on the far end is (at least close to) 50 ohms, he can put another 9:1 balun over there, at which point his 95% number will be accurate... I'm only mentioning this here as he didn't say he did this.

LMR-600, with a 1:1match on the antenna side, 100 watts in will get you 87.096 watts out, which is better than the 450 ohm line with no 9:1 balun on the far end...

Ladder line, and its variants are amazing, better in many ways than coax (especially cheaper). Unfortunately it seems to be a lost art these days, which is a shame.


The DB

 

[Shadetree Mechanic]

Here is some info about ladder line.

Ham Radio Site - {D-i-Y Ladder-Line}

Neue Seite

www.dj0ip.de

 

[Uncle Ronnie 336]

Why 9:1?

because it's what i had laying around

 

[Uncle Ronnie 336]

What is the antenna feedpoint impedance? That theory works only if you are imposing a 450 Ohm constant at the feedpoint.

close enough for govt work i guess. no higher than a 1.5:1 across 3+ band segments

 

[Uncle Ronnie 336]

According to This coax loss calculator, a 150 foot run of RG8x with a 1:1 match on the antenna end, 100 watts in will get you 58.498 watts absorbed by the antenna. There is 2.32 dB of loss, all of it from the initial pass through the coax.

According to the same calculator, a 150 foot run of 450 ohm window line (which many now days is mistakenly called ladder line) into a 9:1 match (50 ohm load) on the antenna end, 100 watts in will get you 81.077 watts absorbed by the antenna. Here there is 0.911 dB of total loss, 0.221 of which is from the run through the feed line, and 0.69 is losses from the reflected power as it travels through said feed line.

That is where the op made a mistake in numbers, you can't assume the match for both feed lines of different impedances to the same load will be the same. Of course, assuming the load on the far end is (at least close to) 50 ohms, he can put another 9:1 balun over there, at which point his 95% number will be accurate... I'm only mentioning this here as he didn't say he did this.

LMR-600, with a 1:1match on the antenna side, 100 watts in will get you 87.096 watts out, which is better than the 450 ohm line with no 9:1 balun on the far end...

Ladder line, and its variants are amazing, better in many ways than coax (especially cheaper). Unfortunately it seems to be a lost art these days, which is a shame.


The DB

i had some coax on the shopping list but this was just a very successful experiment and i now cannot justify the cost of that long of a run of LMR600. i want some other people to mess with it, maybe optimise it some. a folded dipole is resonant, but at about 200-300 ohms so most people use a 4:1. what i did was slap a bunch of stuff together and shrugged as EVERYONE locally came up drastically from the long run of 8x on an imax.

 

[Uncle Ronnie 336]

so how i keep the shape of a folded dipole was to wrap it lengthwise across 2 sections of PVC conduit to make it easier to hang vertical. so far i have not encountered any other CBers going this route.

 

[FlatlandBusa]

I run legal limit+ to a non resonant ladder line fed doublet on 10 - 160 and have had zero issues with RF in the shack on any of the bands. An ATR-30 tuner keeps the linear happy. This antenna hears good and gets out really good. The only band I need to be cautious on is 160 as the feed line and tuner get warm on long key-downs at legal limit. Ladder line is a good solution for the feed line of a low visibility non resonant wire antenna.

 

[SuperLid]

I run legal limit+ to a non resonant ladder line fed doublet on 10 - 160 and have had zero issues with RF in the shack on any of the bands. An ATR-30 tuner keeps the linear happy. This antenna hears good and gets out really good. The only band I need to be cautious on is 160 as the feed line and tuner get warm on long key-downs at legal limit. Ladder line is a good solution for the feed line of a low visibility non resonant wire antenna.

I use a doublet with ATR-30 as well. However, I rewound the crappy balun with coax. I tested the as built balun as trash. The coax windings were a huge improvement. When I am not using the internal balun with the ATR-30, I use a 1:1 current balun inside between the transmatch of the day and the source.

 

[SuperLid]

According to This coax loss calculator, a 150 foot run of RG8x with a 1:1 match on the antenna end, 100 watts in will get you 58.498 watts absorbed by the antenna. There is 2.32 dB of loss, all of it from the initial pass through the coax.

According to the same calculator, a 150 foot run of 450 ohm window line (which many now days is mistakenly called ladder line) into a 9:1 match (50 ohm load) on the antenna end, 100 watts in will get you 81.077 watts absorbed by the antenna. Here there is 0.911 dB of total loss, 0.221 of which is from the run through the feed line, and 0.69 is losses from the reflected power as it travels through said feed line.

That is where the op made a mistake in numbers, you can't assume the match for both feed lines of different impedances to the same load will be the same. Of course, assuming the load on the far end is (at least close to) 50 ohms, he can put another 9:1 balun over there, at which point his 95% number will be accurate... I'm only mentioning this here as he didn't say he did this.

LMR-600, with a 1:1match on the antenna side, 100 watts in will get you 87.096 watts out, which is better than the 450 ohm line with no 9:1 balun on the far end...

Ladder line, and its variants are amazing, better in many ways than coax (especially cheaper). Unfortunately it seems to be a lost art these days, which is a shame.


The DB

I mentioned in this thread I have a doublet with transmatch, feeding 450 ohm balanced line, using the 1:1 internal balun in one of my setup configurations. It is great.... no headaches and just does what it is supposed to.

 

[M0GVZ]

dropping the feed loss from 42% to 5% is HUGE.

Half a S point on a S-meter calibrated to IARU standards, 1 S point on a typical CB meter.