Designing for a Certain Impedance (

Jerry, KA4OBT, is wondering why some one would use a 200 ohm antenna instead of a 50ohm antenna. His second question is where can he find an equation for calculating the length for a 200 ohm antenna.
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[@FoxUSArmy]

I think the main reason for 4:1 baluns could be that old school hams had plenty of 300 ohm window line for their broadcast TV antennas and 75 ohm coax became readily available. Matching those is 4:1. Hams liked to homebrew with what they had lying around on hand. Seems reasonable enough (and I may have read something to that effect years ago).
Now... Why do we still do it? Change is really hard when someone takes the time to learn one way of doing something. And it doesn't hurt to have 4:1 in your TUNER as it more than covers the 1.5:1 for a dipole to tune 50 ohm and helps you bring 300 ohm close to within tuning range of 50 ohm as well. So it's probably a good compromise that covers the most common scenarios.
Just a thought.

[@billmcilwee566]

Thanks for another informative video. 73, KF0NNQ.

[@rudiwiedemann8173]

OMG Dave! It's EASY to build a Balun or Unun for darned near ANY impedance conversion ratio you like. The impedance ratio is just the square of the turns ratio. UnUns have a shared ground connection and BalUns don't. It's that simple! For example, if I wanted to feed an OCFD at around 15% from one end which exhibits an impedance of 1,250 ohms (at your desired frequency), that's just 50x25. So the turns ratio is the square root of 25 which is 5. You can get this with a simple 3 turn primary and 15 turn secondary. And the turns ratIo doesn't even have to be in integer number. It all derives from Ohm's Law and the fact that the power across any transformer must be the same on both sides...73 from K7RAW-The Antenna Whisperer (see my Channel for my full TennaTalk Series)

[@rjy8960]

I've been looking at designing a delta loop and am of the impression that in certain configurations they present a 200R impedance which is what I'm most likely going to go with.
Thanks Dave!

[@N2YTA]

Isn't an other than 50 ohm antenna (or feeding a dipole at other than the center) a trade off necessary to make the antenna multi banded?

[@dandypoint]

I think the answer is yes. I have seen 4:1 baluns used on Off Center Fed antennas where you attempt to pick a feed point near 200 ohms on as many bands as possible. Then the 4:1 transformer reduces that to near 50 ohms. All you really need is to end up with a range from 25 ohms to 100 ohms and your coax SWR will be less than 2:1. So if the antenna feed point range can be anywhere from 100 ohms to 400 ohms.
If it is 100 on one band you get 25 ohms and a 2:1 SWR. If the antenna on another band is 400 ohms you get 100 ohms and a 2:1. If the feed point ends up above 100 and less than 400 you get a better than 2:1 SWR. Sometimes open wire line is used as a transformer with an OCF dipole to make an impedance transformation and then the 4:1 balun will see a value closer to 200 ohms and can convert it to very nearly 50 ohms. There are lots of possibilities. Myself, I use broadband Beverage on the Ground receiving antennas on 160 through 40 meters and their input impedance is near 300 ohms so I wind 4:1 transformers for them because I use 75 ohm RG-6 for my receiver antennas.