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Homemade Radar

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Homemade Radar

Unread postAuthor: SEAKING9006 » Sun Sep 21, 2008 12:00 pm

I've been interested in radar systems for quite some time, being an avid WWII tech fanatic, (A fact that causes me to drool over turbojet engines, radars, and guided air-to-air missiles) and have unfortunately found nothing in the way of a kit or set of plans for a home-brew radar station. Most of what I find ends up being either a police radar jammer or a speed radar. What I'm looking for is something with a graphic output that I can look at and see if something is flying overhead.

In an unrelated note, progress on any of my current projects has been slowed by a combination of endless school work, laziness, and my participation in my schools BEST Robotics team. I have however found a supplier for large pressure rated fittings, and a backpack reservoir (my new R808 and R808 A1 backpack air tanks) is currently under construction. Once I find the time, I will resume work on my blowforward valve automatic.
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Unread postAuthor: TurboSuper » Sun Sep 21, 2008 1:22 pm

Well, the little problem is that the authorities won't like your radar signal interfering with their radar/communications. You'd have to check with the FCC for what band you can use and the max range you can use it in.
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Unread postAuthor: SEAKING9006 » Sun Sep 21, 2008 1:29 pm

That may not be the case, seeing as unless I build a really old style (chain home) radar, or phased-array (not going to happen), there shouldn't be an issue with interference. Also, radar usually only functions on specified frequencies. The frequency capable of detecting light aircraft should not interfere with communications.
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Unread postAuthor: jimmy101 » Sun Sep 21, 2008 2:13 pm

You can't, legally, generate and transmit RF in most places in the world. There are only a few exceptions to this. You are allowed to generate RF in narrow frequencies bands such as used by walkie-talkies, Ham etc.

Blasting out enough RF, at suitable frequencies, for a homebrew radar is going to have the feds knocking at your door.

Are you an expert in cross talk between RFs at different frequencies? Do you know how to measure the sideband power of your transmitter? Transmitters do not put out a single frequency. They give harmonics, noise, random glitches etc. Any transimitter with enough ooomph to be used in radar, even if the range is limitted to a few thousand feet, is going to f-up all kinds of electronics devices within a couple miles.

My cell phone puts noise into my PC's soundcard. The cell phone is transmitting at what, gigahertz? The soundcard is working at killohertz. Big time cross talk even though the frequency ranges are seperated by about a million fold.

There's a reason why most electronics sold in the US have FCC stickers on'm saying they meet the restriction on RF generation. Even things that aren't meant to be transmitters (TVs, PCs, stereos...) still have their transmission characteristics measured.
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Unread postAuthor: psycix » Sun Sep 21, 2008 2:37 pm

Well, I wouldnt really worry bout the legality.
Spudgunning isnt always legal either, yet still, may people do it.
I'd say do not run it too much and too long, so that if you would cause interference, they do not have the time to track you.
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Unread postAuthor: grumpy » Sun Sep 21, 2008 3:43 pm

building your own DARTS radar is perfectly legal as long as you have a amature radio license, some info and stuff can be found here.
http://www.hamhud.net/darts/rdr_comp.htm
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Unread postAuthor: SEAKING9006 » Sun Sep 21, 2008 8:36 pm

Well, legality happens to be a serious issue, as far as my current situation is concerned, especially when it comes to electronics. (Why do you think I only build pneumatics? :wink: ) Anyway, I could probably get what I want out of a fish finder modified for atmospheric use, or just a surplus radar set.

Oh well. Not really a huge concern of mind, mainly a passing fancy.
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Unread postAuthor: Solar » Sun Sep 21, 2008 10:08 pm

How is a boat radar different than what you are talking of building? 24 to 50 miles on the water is legal to operate?. Is the technology different?
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Unread postAuthor: starman » Mon Sep 22, 2008 12:46 am

Solar wrote:How is a boat radar different than what you are talking of building? 24 to 50 miles on the water is legal to operate?. Is the technology different?


Isn't boat radar aimed fairly close to the ground so as to just pick up other boats and land masses? I'm sure it's properly regulated via the FCC just like everything else.

@Seeking: I'm curious how a real radar setup would be even remotely useful to an amateur hobbyist...beyond just the novelty of it of course. I'm guessing there is a real reason you don't see home brew radar station plans in Popular Electronics. Ditto Jimmy on this.
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Unread postAuthor: jimmy101 » Mon Sep 22, 2008 2:30 pm

Solar wrote:How is a boat radar different than what you are talking of building? 24 to 50 miles on the water is legal to operate?. Is the technology different?

Boat radar, aircraft radar, ground radar, deep space radar, they are all basically the same.

The key point is that those are all licensed intruments. Built by people that know what they are doing and tested by other people to insure they only broadcast in the claimed frequency range.

Comparing spudgunning to a homebrew radar is a bit of a stretch. The gun's range is typically several hundred meters and the chances of actually hitting anything at that range is pretty close to zero. The radar may well have a range of several miles (or more) and will "hit" everything within range. The radar may have fairly minor affects on your neighbors, like interfering with TV and phone signals. Or, it might have a significant affect like interfering with an aircraft's radar or confusing a person's pacemaker.

If your homebrew set overlaps the frequencies used by air traffic control radars you'll have very angry federal employees at your door in an instant. The feds would be able to pinpoint your location to within a fairly small area even if you only transmit for a few seconds. Your radar set is going to look like a big-ass radar beacon and could be located by triangulation from the various local aircraft control radars and weather radars. Where I live, an unlicensed radar transmitter would light-up something like ten local radar stations.

I'm about 20 miles from an aircraft gunnery range. I'm sure those folks would be very displeased if an unlicensed radar set started blasting out RF.

If the technology interests you, you might consider doing ultrasound instead. The range is very limited (probably less than 100 meters if you're really good) but the principles are all the same, and it is unregulated. (Of course, your dog might not like it much :shock: )
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Unread postAuthor: TurboSuper » Mon Sep 22, 2008 3:29 pm

How about using optics? I remember someone built a sentry gun using a webcam...I'm sure you could cook up something similar with the right coding.
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Unread postAuthor: Hotwired » Mon Sep 22, 2008 9:32 pm

I have a suspicion that would have been just motion sensing, you can make a bot to "aim" roughly using an array of motion sensors around it. If it was actual target recognition that would be something to see.
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Unread postAuthor: TurboSuper » Tue Sep 23, 2008 5:15 am

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Unread postAuthor: Hotwired » Tue Sep 23, 2008 8:23 am

Haha, the clip is amusing :P

*sneaks past it using a sheet of A4 paper on a stick while dressed in dark clothing*

Cool stuff all the same but you'd need a fair bit of non mechanical knowledge including coding to rig up one.
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Unread postAuthor: rpjacks » Tue Mar 29, 2011 9:57 am

I was a Radar Repairer in the U.S. Army for 18.5 years and have some observations based on comments here.

Transmitters do not have single frequencies, they are able to utilize a single freq at a time. The tuner determines the output freq for the transmitter/antenna.

Current radar sets prevent contamination of signal by using multiple frequencies so that the outgoing signals are not the same as the signals being received at that same instant. For example my radar set is sending out pulses using 10 freqs, it sends out "1,9,3,0,2,8,7,4,5,6" it recorded he order and looks for those freqs in that order on return, and discards any signal not in sequence, which is why my radar set could be within range of another set and not interfere with each other (in my case it was artillery radar and our systems faced each other so that we covered each other within our fan)

Broadcasting anything through a radio transmitter is restricted by the FCC. Limit your frequency use to bands authorized by the FCC and keep your wattage within their guidelines and you can do anything you wish, regardless of what that is, unless your actions are preventing others from using the designated Citizens Bands or infringing upon the bands authorized for government use. If it were illegal to create or use radar, every batting range, race track an anyone else using speed detection radar would be being tracked by the government constantly and deadlocking those agencies. It is estimated that over 1.5 million radar units of various kinds (speed detection, object finding, GPR and other) are in non government use within the United States alone, it is not a crime.

By the way, many motion detecting doors use s basic radar device to open the door. Most of these are now using infra red motion detection but any that are immune to IR interference are likely to use RF motion detection.


As I can see from your posts that you are electronics gifted, you probably have as good a chance as anyone to do that which you wish to do, here is my suggestion.

Start small. Purchase a speed radar unit, like a Hot wheels radar (about $20 look online) and locate the output circuit. 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. What you want to do is channel that output to something like an Arduino where you can program an output to a screen instead of just a number display. You will further want to eliminate the "dead return" suppression. That is the part of the system which is preventing the wall from being registered by the radar gun.

Some of the simple radars used in the army are small ground based sensors which can and are used to detect man sized objects moving in a set location. These sets can be used to map a target area, then switched to eliminate those objects in it's field of view which are stationary from the feedback. I have limited experience with the use of these sets but in my school experience we used them and they are incredibly accurate. We mistakenly aimed the set slightly higher than normal and ended up getting helicopter returns when they were in the area. I don't know if these units would work with fast moving jets, but cars and helicopters are certainly valid targets.

By experimenting inexpensively with the radar gun, you will gain knowledge of RF and how the sideband is produced. If you can find tech manuals on those radar guns, or old ground based Army manuals (hard to come by as they are usually classified) you will get the idea of what you need to build your own. Just remember if you start building big, you will be using high voltage and all safety warnings should be doubled. If you are building your own stuff, make sure you design safety interlocks to prevent HV accidents. Even small artillery radar sets use extremely high voltages so please be careful.

I hope you found this useful, I loved working on radar sets and when I purchase my own home I hope to build a workshop where I may build m own small unit. The information I gave above concerns single direction radar, I have no experience with rotating antenna systems nor do I know how to make a graphic interface.
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