[hamdani yusuf (OP)]

Continuing my effort to understand the behavior of microwave in another thread, here I'd like to share experiments showing how radio wave behaves. I've prepared some experimental equipment, but didn't have enough time to execute the experiments yet, so for now I'll put this well made video from Harvard Natural Sciences Lecture Demonstrations first.

[hamdani yusuf (OP)]

Here is another demonstration from a documentary movie.

Credits: Artifax Production for Channel 4 - 1990

[hamdani yusuf (OP)]

My plan is to repeat those experiments with various shapes and materials of antennae. I hope it can complete our understanding of how radio waves work. In my previous experiments using microwave, we investigated its interactions with various combination of materials and shapes, but the transmitter and reciever antennae have fixed materials and shapes.

[hamdani yusuf (OP)]

I was about to start the experiment using these generic 433 MHz radio transmitter and receiver,


and the circuit diagram (transmitter on the right)

when I realized that their antenna feeds are unbalanced, which are not well suited for dipole antennae. Using monopole antennae is simple and convenient for practical use, but they introduce unwanted complexities which are against the purpose of the experiments. After searching for a while I finally found this source which I think is the best solution for the problem.
http://vk5ajl.com/projects/baluns.php#current

CORE TYPE CURRENT BALUN
Highly recommended. This is a very low loss balun and ideal for use with a tuner.

This balun works by controlling currents. THERE IS NO TRANSFORMER ACTION. The two windings must be in the same sense (dots at the same end). The magnetic fields of opposing balanced working currents will cancel each other out and so present very little impedance (other than the resistance of the wires) to these currents. On the other hand, common mode currents will produce a mutually inductive magnetic field and face a high impedance.

This means the more turns the better, up to a point. In this case, the windings are a transmission line that has losses but these are much lower than the losses transfering energy from one winding to another through a core.

Design considerations are really very minimal. Since the losses of balanced lines are low compared to coax, you aren't losing much except for the resistance of the wires which is very low compared to radiating resistance anyway.

The current balun shown here, wound around a steel bolt, is probably a little crude but why not? Steel or iron is not normally used for RF because there are too many eddys making it too inefficient for transformers. In this application, since there is no magnetic effect for the desired currents, it doesn't matter. For common mode currents on the other hand, inefficiency is an advantage. Not only is a high impedance presented to common mode currents, the energy from them is absorbed by the bolt.

I'd like to hear if someone here has a second opinion.