Originally Posted by Lockpicker
I am currently working on a TV antenna of a Omni directional nature. I have built three Hovermans, two Danny Hodges - whisker antennas and am now working on a circular design out of copper tubing.
Hello, Lockpicker; welcome to the forum.
Now I have taken a step back to think about the balun ......Every antenna build I find on the net says to use the 75/300 ohm balun.....
Many DIY antennas have an output impedance of 300 ohms, so the proper balun for them would be 300 to 75 ohms, or 4:1. Some DIY antennas have an output impedance of 75 ohms, so the 300/75 ohm balun would not be correct for them.
Also my balun is the new style and continuity of each side is .5. If it is a 4 to 1 or say 75 /300 ohm then readings should be 4 to 1 and not evenly matched as mine presents. Thoughts ?
When you use an ohmmeter to measure resistance, that is the DC resistance. The readings that you get with an ohmmeter are not conclusive because the internal wiring of the balun is different for different baluns.
The impedance of antennas is measured at RF frequencies with an impedance bridge, not an ohmmeter.
I am currently working on a TV antenna of a Omni directional nature.....how do they measure it when there is dead air between each side ??
The air between the two sides of a dipole isn't dead; there is a current flow through the air between the two sides of a dipole; the impedance at the feedpoint is 75 ohms. The current flows through the capacitance between the two ends:
With a folded dipole, a connection between the two ends is made with a second dipole in parallel with the first dipole; the impedance at the feedpoint is 300 ohms. Even with the folded dipole there is current flow through the air because of the capacitance between the two ends that are at a different potential (voltage).
am now working on a circular design out of copper tubing.
What does that design look like?
I must tell you that I am not a fan of Omni antennas; they receive poorly in all directions. If your desired channels are in different directions, you will usually need to find a different way to solve the reception problem.