Simple UFO Detector |
Overview
Ever wanted a device which you could point at an unknown light in the sky and have it tell you if it's an UFO?
Well, now you can build one! Kinda...
By adding a simple phototransistor to one of the eyepieces on an old pair of binoculars, and coupling the phototransistor's output into the "Simple Optical Receiver Project #1" from GBPPR 'Zine, Issue #87, you'll have a device which can be used to monitor any modulation(s) of the target light in the sky.
What makes this an "UFO detector" is the fact that some large commercial and military airplanes have lights (landing, navigation, etc.) which are modulated at 400 Hz.
In order to reduce weight (and increase efficiency) of an airplane's electrical system, they tend to use a 400 Hz modulated 120 VAC buss, as opposed to the standard 50/60 Hz 120 VAC you see from your wall outlet. The higher the frequency of the AC signal, the physically smaller the transformer needed to step-up or step-down the AC voltage. The equals a significant reduction in unnecessary weight for the airplane.
That was a pretty quick overview, and you can Google for hundreds of more articles on airplane electrical systems, but all you really need to know is that SOME of the lights on an airplane sound like a 400 Hz tone when you "listen" to them via a phototransistor-based optical receiver. Not all planes use a 400 Hz AC electrical system, with smaller airplanes being run from +12 or +24 VDC batteries. Since those smaller planes tend to have propellers, you should be able to use your ears to weed them out from UFOs. In some cases, it's possible to "hear" the vibration in the lights caused by the propeller.
Mirages and "floating" lights from atmospheric conditions or temperature inversions will tend to have a 50/60 Hz (or 100/120 Hz) modulation as the illumination source is often just regular lights on the ground.
Some filament-based car headlights will have a "brrrr..." modulation as the road vibrations modulate the headlights.
Military illumination and counter-IR flares may have a "crackling" modulation, but I don't have a way to test this right now.

Pictures & Construction Notes

Overview of the parts for the UFO detector.
Above is an old pair of Bushnell 7x35 binoculars and a 1-inch PVC cap.
The binoculars should have rubber eyepiece cups which can be unscrewed, as shown on the left.

Paint the inside of 1-inch PVC cap with some non-reflective paint.
Mask off the rim of the PVC cap so you have a clear area to glue the rubber eyepiece cup inside the cap.
You'll also want to drill a hole (either 3/8" or 1/2") for mounting a BNC jack in the center of the flat side of the PVC cap.

Glue the rubber eyepiece cup just inside the 1-inch PVC cap.
Be sure the eyepiece cup is flush with the top of the PVC cap.
Also be sure not to get any glue on the eyepiece cup's threads.
If you're lucky, you'll have a perfect fit. If the PVC cap is too large, you'll have to wrap a few layers of electrical tape around the eyepiece cup.

On the front of the PVC cap, an isolated BNC jack will be mounted.
The collector (flat-side) and emitter of the phototransistor (Radio Shack #276-145) will be attached to the isolated BNC jack. You'll need to guesstimate the phototransistor's final lead lengths.
An isolated BNC jack will allow for more options in configuring the phototransistor for the post-processing electronics, and is highly recommended.


Mounting the phototransistor inside the 1-inch PVC cap.
The phototransistor should be mounted just a few millimeters away from the glass of the eyepiece. You may want to fiddle and experiment with the final mounting distance.
Adjust the threading distance on the eyepiece to give you a bit of a "fine tune."

Completed UFO detector.
Screw the new eyepiece onto the binoculars and connect the output from the phototransistor to the optical receiver.
Test the unit by viewing a distant terrestrial light source you know is modulated at 60 Hz. While viewing the light source in the "normal" eyepiece of the binoculars, you should also "hear" the 60 Hz modulation of the light in the audio output from the optical receiver.
It's also possible to analyze the target light source via computer audio spectrum analysis software. This is a good way to create a catalog of known objects which you can quickly reference.
Another trick is to add a small piece of diffraction grating and a small color digital camera over the binocular eyepiece. This acts as a "poor man's spectroscope" and allows you to study the different wavelengths which make up the target light you are monitoring.
Sodium-vapor lamps, like those found in most streelights, will have a strong color spectrum in the yellow-orange-red bands along with a distinct turquoise band. Neon lights tend to have a single color or several bands of distinct colors. Mercury-vapor lamps tend to have several bands in the blue-violet spectrum.