Yagi 101

[KX5JT]

Here is very en'light'ning demonstration of how a Yagi works.  It uses a small light bulb on a dipole and a 5 watt 2 meter signal.

http://blog.makezine.com/archive/2010/02/seeing_radio_waves_with_a_light_bul.html

[K1JJ]

That's quite a dramatic demonstration that everyone should view. It makes one want to go out and put reflectors and directors on all our dipoles...

It's amazing how well the energy is attenuated off the rear of the Yagi.  Notably, the demonstration shows how the attenuation begins behind the driven element itself, not behind the reflector.

T

[KX5JT]

That's quite a dramatic demonstration that everyone should view. It makes one want to go out and put reflectors and directors on all our dipoles...

It's amazing how well the energy is attenuated off the rear of the Yagi.  Notably, the demonstration shows how the attenuation begins behind the driven element itself, not behind the reflector.

T

I didn't think about that until you pointed it out Tom.  It does seem a little counterintuitive.... I guess I always thought of the energy bouncing back from the "reflector" but I suppose it if does "bounce back" then it's out of phase and cancels as it reflects back upon itself in that space between the the reflector and the driven element.... my brain hurts.

[Steve - WB3HUZ]

It is a nice demonstration but a little misleading. The bulb is often in the near field of the antenna (not to mention there may be some reflections happening), so it's not showing the true far field pattern - the one that actually matters.

It's amazing how well the energy is attenuated off the rear of the Yagi.  Notably, the demonstration shows how the attenuation begins behind the driven element itself, not behind the reflector.

T

[KL7OF]

Those leggings that she wears are skewing the pattern.....Otherwise a pretty neat demo..