300 ohm ladder line on 11 meters ?

[HomerBB]

Just for fun I decided to try a twinlead to a wire antenna. For 2+ months I've had 300 Ohm twinlead attached to my rectangular loop in my attic. It is then attached to a coax choke 75 Ohm 1/4 wave transformer turned into a coax choke and fed from the radio with 50 ohm jumper.

It gives me a very good 1.1:1 SWR over a sufficient bandwidth and I routinely run up to 400 watts PEP though it with no problems.

Whether it's supposed to work or not, or is incorrectly done, I'm all about trying things and this one works very well.

 

[Needle Bender]

A common mode choke only keeps the portion of the feedline, coax cable,between the choke and the transmitter from radiating. That is why they are used at antenna feedpoints. Once the balance of a balanced line is upset it will radiate regardless of the presence of another CMC on the other end. It is a good example of two wrongs not making a right.

Without trying to be offensive, it sounds to me like you're talking in circles. You keep mentioning the balance is "upset" but don't offer the reason why, other than the balance is upset.

If the 5000 ohm choke is right at the coax tap point at each end so there is no unchoked coax to radiate on either end, then there's no evident reason why the balanced line would see more than a negligible unbalanced current path at either end to cause it to go unbalanced and radiate.

I'm going to build and try it and I'll report back when I do later in the Spring if not sooner, win or lose.

I have to admit, I'm cheating a little since I already know it works, there's 360 yards of 450 ohm fed this way at a dx cabin I've been to which replaced LMR400 because of too much loss to the 10m beam on top of the hill (1200w of 1500w power loss) but I wasn't the one who built and matched that line, and I want to try it for myself.

I want to see how hard it is to find the 50 ohm tap point at each end and if it moves or changes once the other end is tapped.

I'll be using 300 ohm TV twin lead (because I have 500' of it!) with 100w and will see what amount of loss there is by reading how much wattage is present at the other end of 500'.

I'll find a park and lay out the 300 ohm in a big elevated triangle so the antenna end is close enough to me to read the watt meter, unless I can get someone to go with me in which case I'll just lay it out straight. I have another Gainmaster I'll probably use on a 6' pipe hammered into the ground.

I'll also walk the 500' of twin lead with a field strength meter to check for feed line radiation.

 

[Captain Kilowatt]

Just for fun I decided to try a twinlead to a wire antenna. For 2+ months I've had 300 Ohm twinlead attached to my rectangular loop in my attic. It is then attached to a coax choke 75 Ohm 1/4 wave transformer turned into a coax choke and fed from the radio with 50 ohm jumper.

It gives me a very good 1.1:1 SWR over a sufficient bandwidth and I routinely run up to 400 watts PEP though it with no problems.

Whether it's supposed to work or not, or is incorrectly done, I'm all about trying things and this one works very well.

Sounds to me like your 75 ohn transformer is a balun which will preserve the balance of the 300 ohm cable. You did it right

 

[Captain Kilowatt]

Without trying to be offensive, it sounds to me like you're talking in circles. You keep mentioning the balance is "upset" but don't offer the reason why, other than the balance is upset.

If the 5000 ohm choke is right at the coax tap point at each end so there is no unchoked coax to radiate on either end, then there's no evident reason why the balanced line would see more than a negligible unbalanced current path at either end to cause it to go unbalanced and radiate.

I'm going to build and try it and I'll report back when I do later in the Spring if not sooner, win or lose.

I have to admit, I'm cheating a little since I already know it works, there's 360 yards of 450 ohm fed this way at a dx cabin I've been to which replaced LMR400 because of too much loss to the 10m beam on top of the hill (1200w of 1500w power loss) but I wasn't the one who built and matched that line, and I want to try it for myself.

I want to see how hard it is to find the 50 ohm tap point at each end and if it moves or changes once the other end is tapped.

I'll be using 300 ohm TV twin lead (because I have 500' of it!) with 100w and will see what amount of loss there is by reading how much wattage is present at the other end of 500'.

I'll find a park and lay out the 300 ohm in a big elevated triangle so the antenna end is close enough to me to read the watt meter, unless I can get someone to go with me in which case I'll just lay it out straight. I have another Gainmaster I'll probably use on a 6' pipe hammered into the ground.

I'll also walk the 500' of twin lead with a field strength meter to check for feed line radiation.

Note that I never said your ideas will not work,never did, as it will. There is working and then there is working as it should. Take two RF current meters and put one in each side of the balanced line section and see the currents are equal.

 

[HomerBB]

Sounds to me like your 75 ohn transformer is a balun which will preserve the balance of the 300 ohm cable. You did it right

Whew! I get lucky sometimes.

 

[Needle Bender]

Just for fun I decided to try a twinlead to a wire antenna. For 2+ months I've had 300 Ohm twinlead attached to my rectangular loop in my attic. It is then attached to a coax choke 75 Ohm 1/4 wave transformer turned into a coax choke and fed from the radio with 50 ohm jumper.

It gives me a very good 1.1:1 SWR over a sufficient bandwidth and I routinely run up to 400 watts PEP though it with no problems.

Whether it's supposed to work or not, or is incorrectly done, I'm all about trying things and this one works very well.

Sounds to me like your 75 ohn transformer is a balun which will preserve the balance of the 300 ohm cable. You did it right

No, a choke is not a balun and a balun is not a choke.
But, uhm, that's basically, exactly what I've been describing, except I don't need to use a 75 ohm 1/4 wave impedance matching transformer since there is a 50 ohm antenna at the other end, not a 100 ohm loop, plus I'm using a shorted stub termination with a 50 ohm tap. But they're both still balanced to unbalanced (coaxial) line with a cmc choke where they meet.

Note that I never said your ideas will not work,never did, as it will. There is working and then there is working as it should. Take two RF current meters and put one in each side of the balanced line section and see the currents are equal.

So for Homer's cmc-choked, balanced to unbalanced feed line you say, "You did it right",
but for MY cmc-choked, balanced to unbalanced feed line you say, "There is working, then there is working as it should".

Now you're just blowin' hot air. I'm done. :glare:

 

[Captain Kilowatt]

No, a choke is not a balun and a balun is not a choke.
But, uhm, that's basically, exactly what I've been describing, except I don't need to use a 75 ohm 1/4 wave impedance matching transformer since there is a 50 ohm antenna at the other end, not a 100 ohm loop, plus I'm using a shorted stub termination with a 50 ohm tap. But they're both still balanced to unbalanced (coaxial) line with a cmc choke where they meet.


So for Homer's cmc-choked, balanced to unbalanced feed line you say, "You did it right",
but for MY cmc-choked, balanced to unbalanced feed line you say, "There is working, then there is working as it should".

Now you're just blowin' hot air. I'm done. :glare:

Now that I am on the laptop and not on my phone like I was earlier today at work i think I misread this part from homerbb.

"75 ohm 1/4 wave impedance matching transformer" On my tiny screen I read it as "75 ohm 1:4 impedance matching transformer" hence my comments. Anyway I am not just blowing smoke as you say but we are just pissing on each other's boots so we will just agree to disagree and move on. In the end either way will radiate a signal and that is what it is all about.

 

[Needle Bender]

In the end either way will radiate a signal and that is what it is all about.

 

[HomerBB]

Aw Shucks . . .

 

[mackmobile43]

Aw Shucks . . .

You got *MPOWERED

 

[HomerBB]

Just for fun I decided to try a twinlead to a wire antenna. For 2+ months I've had 300 Ohm twinlead attached to my rectangular loop in my attic. It is then attached to a coax choke 75 Ohm 1/4 wave transformer turned into a coax choke and fed from the radio with 50 ohm jumper.

It gives me a very good 1.1:1 SWR over a sufficient bandwidth and I routinely run up to 400 watts PEP though it with no problems.

Whether it's supposed to work or not, or is incorrectly done, I'm all about trying things and this one works very well.

I was rethinking my feedline setup on the attic loop and realized I left something out of the sequence.

Loop>300 Ohm twinlead>4:1 balun>75 Ohm section wound into coax choke>50 ohm jumper>radio = very low SWR and a surprisingly good DX loop in the attic. Not shabby on local either. Downside is the loop is more susceptible to HVAC blower noise being in the attic.

May not be right yet, but it's working well.

Why I rethought it is I want to take the twinlead out to the dipole, too, and as I was thinking of what I needed to put in line it occurred to me I had not written the one piece into my previous post on this thread. You believe me or must I get photos?

 

[Captain Kilowatt]

Earlier I said something to the effect that just because it is not done right does not mean it will not work. Here is a good example of what NOT to do but yet it still worked.

Waaaayy back when I was first licensed I strung up an 80m dipole fed with 450 ohm ladderline. (My how history repeats itself as that is all I have right now until spring) It was erected as an inverted Vee with the apex at 38 feet and the ends almost at ground level. The support was a steel tower stuck right in the middle of the antenna. (Mistake #1) Not knowing too much about ladderline and having only used coax cable before I ran the balanced line out the basement window and over to the tower. It was then taped to a tower leg for about 30 feet to the antenna along with various coax cables and rotator control lines. (Mistake #2 BIG MISTAKE) I had about 15 feet left over in the shack so I rolled it up into a coil about a foot and a half in diameter. (Mistake #3) I used that configuration to work all over the world including an AM contact into Barnaul central Siberia with just 12 watts of carrier from my Heath DX-60. Was it installed right? Not just no but HELL NO!! Did it work? Sure did. It also creamed the television and stereo as well as the old 49 MHz cordless phone and I had lots of RF in the shack and would get bitten by the microphone. Later as I learned what I did wrong I used stand-offs to hold the line away from the tower and shortened the line so I did not need to coil up the line. The problems with the phone and stereo went away and the interference to the television was greatly reduced and was limited to just 80m and some times on 20m. I also had no more problems with getting bitten from the RF in the shack. Antenna performance did not seem to change. If we simply base installation procedures on performance we do not see the entire picture.

 

[Captain Kilowatt]

I was rethinking my feedline setup on the attic loop and realized I left something out of the sequence.

Loop>300 Ohm twinlead>4:1 balun>75 Ohm section wound into coax choke>50 ohm jumper>radio = very low SWR and a surprisingly good DX loop in the attic. Not shabby on local either. Downside is the loop is more susceptible to HVAC blower noise being in the attic.

May not be right yet, but it's working well.

Why I rethought it is I want to take the twinlead out to the dipole, too, and as I was thinking of what I needed to put in line it occurred to me I had not written the one piece into my previous post on this thread. You believe me or must I get photos?

AHHH!! ... So there is indeed a balun in the system. My reading error and subsequent post about doing it correctly was in fact correct after all. BTW with the balun you do not need to make a choke out of the coax cable but no harm, no foul if you do it just won't make any difference.

 

[HomerBB]

I feel better now

 

[Needle Bender]

I feel better now

I feel all warm and fuzzy :tongue: