Mirrors are fascinating. They reflect nano-meter light waves in such a way that three mirrors set at different angles next to a light bulb create the appearance of more light bulbs, reflect the light in several directions and amplify the amount of light being produced.
What is the bandwidth of a mirror? We only observe the light frequencies, but does it also reflect microwaves and lower; maybe UHF, VHF, on down?
What if a 10-foot mirror next to a 10-foot antenna doubled and maybe aimed the signal in a desired direction? How about one of those 3-way mirrors from a department store dressing room. Would that cause a strong AM radio beam in a specific direction?
RF and Mirrors
Carl,
You have good insight on how directive radio antennas work. A mirror does not “amplify” the light rather it redirects it so the intensity adds in a certain direction but in doing so it blocks the light in its shadow. This is the principal of directive radio antennas.
The mirror reflects light due to the interaction of the light energy with the mirror material. This depends on frequency since light can be considered electromagnetic radiation. The mirror absorbs the light energy and reradiates it in a different direction.
Mirrors and metal plates will reflect microwaves and this is used in microwave dishes. At lower RF frequencies reflection also occurs but the efficiency is lower to the point that the reflection is not significant. A near resonant length of conductor will reradiate efficiently and if the reflected wave phase is such that the “reflected” wave adds to the original wave in a particular direction then the intensity will be increased in that direction. But, as with a mirror, the reflecting element will have a shadow (actually produced by interference between multiple waves unlike the shadow of a mirror) in which the field will be nulled. At RF these elements look just like the images in multiple mirrors and in fact this “image antenna” visualization is useful in analyzing directive antenna characteristics.
When we speak of antenna gain we are referring to the increased intensity in a particular direction but the antenna, like the mirror, does not amplify the signal since the total radiated energy is not increased but is just redirected. At low frequencies the spacing between radiating and reflecting elements is important. This is also true with a multiple mirrors but we don’t observe this since the wavelengths are so short and the light is incoherent. For an example of this look up “Newton’s Rings”.
Neil
Reflections
Thank you Neil, I liked the way you explained that. I am always desperate to think of something new to give the part 15 hobby a boost, since we have such small authority.
Next big idea: how can we make AM radio RF VISIBLE TO THE EYE so we could see our signal pattern. Special glasses? Funny dust chemtrailed from an air plane? Looking through an airport body scatter x-ray machine?
Visible AM Radio
Visible AM Radio. I can only imagine how weird and yet cool that would look.
Worth Reflecting
I started thinking again about the mirror idea, so I am bringing this thread back for a re-run.
What about this….
My very first indoor AM part 15 antenna was a white wire, supplied with the AMT3000, simply run vertically up a wall from the baseboard to the ceiling with a glue stick.
If that same antenna were put on a large full-sized mirror, would it make the RF image double inside the room?
Good grief Carly Brown! Your
Good grief Carly Brown! Your such a blockhead!
That wouldn’t be part15 complaint because the mirror image of your antenna would double your antenna system length to 6 meters!
I can see the NOUO report now,
Next big idea: how can we make AM radio RF VISIBLE TO THE EYE so we could see our signal pattern…
I actually had a dream several months ago that I could see the radio waves as kind of a misty, pulsing, swiggling, semi-transparent blueish.. thingy… I was moving my transmitter from one location to another in different areas of the roof, and then observing the signal pattern, and adjusting placement until it flowed precisely the way I wanted it too..
In the same dream, I was able to utilize the large defunct satellite dish sitting up there to better direct my signal towards the north end of the island.
I woke up inspired, and got on the roof while awake.. but I couldn’t see a dam thing.. not even when I squinted my eyes.
Good grief!
Those Dreams
I admit being a blockhead, but I may install a huge mirror and start a fad that could get me on Art Bell. “Mirror Wave Amplifier.”
He amplifies his thoughts and has dates every night.
But your dream is worth going back into to figure out how to make RF visible to the undressed eye.
We must pursue our part 15 ideas, small as they are.
More likely with George
More likely with George Noory. Art Bell is now only re-runs on the C2C “Somewhere in Time” episodes. (so far as I know)
Visible RF?
How about INvisible antennas? If ya can’t measure it’s length, how can you prove it’s not compliant? Now THAT would be an invention!