Homemade Radar

[Technician1002]

Part of what you posted is incorrect..

In speed radar, if you point it at a wall and nothing is moving, the system does not show you the returns from the wall, but if you throw a baseball it will give you the speed based on calculations of the returns of various pulses returned from the object compared to the time the waves traveled.

Most consumer speed radar does not do any ranging whatsoever. Instead of pulsed, the gunn diode runs CW. The transmitted frequency is mixed with the return and the envelope is detected. With no motion the envelope is steady. With motion, a dopplar shift is generated. (Dopplar speed radar) The mixed output of the 2 frequencies is detected. The beat frequency is directly related to the Frequency of the radar and the speed of the object causing a doplar shift. The frequency is counted and displayed as speed.

One other FCC requirement besides interferance with CB or millitary. Any interferance including cordless phones, TV, sound systems, etc is prohibitied. Transmisison on most frequencies are prohibited, except those designated such as the ISM band. (Industrial, Scientiefic, Medical)

Please familiarize yourself with the FCC regulations before building any transmitter. Many (Most) have to be Type Accepted..


Here is a link to get you started and out of jail.
http://www.fcc.gov/oet/info/rules/

Section 15 is in regards to devices.
Section 18 covers the ISM frequencies.

[rpjacks]

I missed this earlier...
Radar does not interfere with pacemakers. Pacemakers are timed circuits to keep your heart beating within a certain range (yes this is frequency but it is not radio frequency). Other than the pacemaker potentially altering the transmitted freq of your attempt at radar and making your returns unreadable, there is no danger. Otherwise pacemakers would be failing on highways and at airports among other places.


Remember that radar is just RAdio Distancing And Ranging. You do need a powerful signal to reach and bounce back to your set when you're talking distances of miles or tens of miles, but when dealing within the idea of hundreds of feet out to perhaps half a mile (based on the wattage restrictions of the FCC) you will not be "painting" aircraft, unless it's the news/police helicopter hovering over your neighbors drug processing shed, and they will not notice that your system even exists unless it's in the freq range that they are using, however as you are restricted to bands they are not using, that is unlikely.

[warhead052]

Take the cheapest radar you can buy, and tweak it a bit to work at higher altitudes and so on. Easy enough right?

[rpjacks]

Technician1002

You are right about the interference issue. As I stated in my reply, as long as you are not interfering with others use of the public frequencies, you are within your rights to do pretty much anything.

I would check your source on TV, Sound Systems, Phones etc, most of these devices have to comply FCC regulation that requires them to not interfere with other objects and that they must be designed as to accept interference from outside sources including interference that may cause the item to not operate as desired.

I am not a government official and admit to not knowing the nuances of all the FCC codes and regulations, nor do I know what freqs are designated as off limits, but I do know there are published lists indicating what freqs are free to use. Any home built radar set of acceptable wattage will not be noticed by any officials as an infringement unless reported or detected. The aircraft in question would never even notice being painted if the wattage allowed such as it would still be in a freq range that the plane would not be "looking for" as a "radar" set.

I think that overall, home built radar is a great project for someone who is in school and wants to work in RF applications in the future, but as for every Tom Dick and Jane, perhaps we should not all dream of being air traffic controllers.

[rpjacks]

Warhead, first of all, aviation radar sets are prohibitively expensive. Second, radar sets are designed to work within a certain range of freq and wattage, you can't do too much "tweaking" to those systems without significant reworking of many subsystems.

The hardest part of building a home radar would be generating the signal and receiving the return, that is why I suggested modding a radar gun. The device is already working as a transceiver for the purpose of radar detection and all you are modifying is the output filter and the display type of that output, which I perceive to be easier for someone working in their home workshop than actually creating and receiving the signals from scratch.

To properly make or maintain the system any other way would require equipment most of us can't justify spending money on, such as a spectrum analyzer used to properly tune both the freq and the information transmitted on that freq.