Those of you who are serious about studying UFOs ( alien space probes? ) have probably wished at one time or another that you could track those lights in the sky on your own RADAR. A rather expensive proposition, but still, it would be pretty good documentation wouldnt it?
O.K. then, how about this, a home made , Bi-Static Radar, that uses a local TV station as the transmitter and your TV set as the receiver. Admittedly, a little crude, but, completely legal , really cheap and it actually works.
First, a little Background
RADAR operates by sending out a radio signal that is reflected back from a target. The most common type sends short, powerful bursts, (called pulses), of radio energy that upon reflection are detected at the same antenna that sent them, ( where they are called echoes, or "returns" ). The time that it takes them to return is a measure of the distance to the reflecting target and the direction the antenna is pointing indicates the direction to the target.
One of the problems facing the early experimenters was the fact that the powerful burst would burn out the sensitive receiver connected to the same antenna. This problem was eventually solved by the invention of the T/R switch.(an extremely fast electronic Transmit/Receive switch) Prior to that however they made do with two antennas,one for the transmitter and a second one for the receiver.The two antennas were seperated by a considerable distance to protect the receiver from the transmitted burst. ( Bi-Static means two places) While this is no longer necessary it still works and is easily arranged.
In fact it is so easily arranged that most of us have done it by accident. Remember back when you had an antenna on your TV? Remember the "ghosts"? A ghost, ( the return ), is a reflected TV signal that arrives later than the direct signal from the station,( the transmitter ), because it is reflected from something,( the target ), thereby taking a detour on the way to your TV set,( the receiver ), and it is offset to the right of the main image because the TV scans the picture from left to right. The distance that it is offset depends upon how long it was delayed by the detour and is (indirectly) a measure of the reflecting objects location. If you put a very directional antenna on your TV and turned it until the ghost was at its strongest the antenna would be pointing at the reflecting object, ( the target ). All you need to do is figure out how to interpret the displacement of the ghost as a measure of distance and you know where the reflecting object is.
The ghosts that most of us have seen in the past were reflections from large buildings, water towers, or passing aircraft. In this application they will be from unidentified lights in the sky.
Most of this discussion is about how to interpret the displacement of ghosts as a measure of distance and the plotting of this information on a map.
The Setup
Imagine if you will a TV with two antennas.Just bring both pieces of coax to a two way splitter with the single input to the splitter going instead to the tv and the two output side going to the two antennas.
One of those antennas should be a standard UHF TV antenna of the "bowtie " variety or whatever variation on this you may have laying around. This antenna should be pointed at a local TV station at least several miles away and will provide the direct path signal to our RADAR. We call it the time base antenna.
The other antenna requires a little work. It needs to be highly directional and might easily be an old 8-10 FT satellite dish with a bowtie at the focal point. This antenna will maximize the ghost and allow us to know the direction to the reflecting object. We call this one the tracking antenna.It needs to be mounted so that it can be steered by the operator.
Using UHF allows smaller, more directional antennas than would be possible with VHF, and by virtue of being a shorter wavelength than VHF, UHF reflects well from smaller objects.
You might also consider adding a VCR to the hookup so you can analyze things later and also provide some kind of evidence that you actually saw something.
The Geometry of it all
To those who hate math, please allow me to begin by offering my deepest and most humble apologies. There is no way to avoid a discussion of ellipses and their mathematical descriptions. I will try to stick to plain english as much as possible. In the end I will leave you with some useful formulas that you can use without following the derivations and a simple computer program that will do all of the arithmetic for you! Please bear with me.
Operating Procedure
You will need at least 4 people to run this system in the field:
It is probably safe to say that there will be others in the area too, many of whom will be looking for potential targets.We can add them to the list and call them SPOTTERS
STEP 1
When a SPOTTER finds a target he/she would point it out to the TRACKER who will then bring the TRACKING ANTENNA to bear on it. When the antenna is on the target the TRACKER will announce "ON TARGET" and then call out the TRACKING ANTENNA direction for all to hear.
STEP 2
The GHOST READER, COMPUTER OPERATOR and PLOTTER will now know that the system is on a valid target and not just staring off into the sky.
The PLOTTER will mark the TRACKING ANTENNA direction on the map and wait for the range information to plot the target location.
The GHOST READER will begin reading the ghost displacement from the screen.
The COMPUTER OPERATOR will enter the TRACKING ANTENNA direction into the computer.
STEP 3
When the GHOST READER has the displacement, he/she will call it out to the COMPUTER OPERATOR who will then enter it into the computer.
STEP 4
When the computer outputs the range information the COMPUTER OPERATOR will call it out to the PLOTTER who will mark the range on the direction line already drawn in step 2.
STEP 5
The PLOTTER should then announce "PLOTTED" so that the TRACKER is free to call out "ON TARGET" again as he/she continues to follow what is probably a moving target.
Some kind of homemade military type jargon would work well here. The point being that everybody should understand everybody else. People who work together for a while usually work these things out pretty automatically.
Alternative designs
For those with a bit of cash to spare, you might consider using two TV/VCR combinations and a dual trace oscilliscope to assemble your RADAR.In which case you would connect each antenna to a seperate VCR and feed the video output from each VCR to a different trace on the scope. Then trigger the trace from the time base signal (direct path). This will greatly simplify the reading of the timing information as the TV sync pulses are easier to see on the scope than ghosts on a TV and the timing can be read directly from the scope face.
It also seems to me that we could use the time base signal to gate an oscillator into a counter and the tracking signal to stop the counter and then read it directly into a computer for calculation of target range! If the antenna direction were also encoded into another port, all that we would need then is a manual input to tell the computer that we are on a target and it could do all the work.I said "it seems to me", I did not say that I have ever tried it.
It ought to be possible to do the same thing with a bench counter and then read the numbers by eye.
If any of you try out the ideas suggested on this page please email me and let me know how it goes for you, specially if it makes you think up any NEW ideas !!! I would like nothing better than to hear of a better way to do this.
And "Ghost Reader" is a little funky, if anyone can suggest a better term I would appreciate that too !