DIY Radar speed gun, anyone interested?

[XJet]

A few months ago I bought one of those cheap Mattel HotWheels radar guns to see if it would be any good for clocking the speed of model airplanes.

Unfortunately they're not. The microwave source is *very* low-powered and the antenna system quite fundemental -- which results in a range of around 30 feet or less when used with something that has the radar profile of a typical RC model airplane.

So I set about designing and building something better.

Google was not my friend -- I could find no other DIY radar guns on the Net so here's what I've come up with so far.

I'm using a 20dB waveguide horn coupled to a gunn diode X-band module (about 8mW output power).

This module also has a mixer diode so it's easy to extract the difference between the transmitted and received signals (the doppler shift).

I've used a two-stage J-FET op-amp based low-noise amplifier to boost the signal from the mixer and (for the time being) I'm then feeding that into the logic board I ripped from the Mattel unit.

Today I tested the setup out at the local airfield. I could reliably measure the speed of full-sized aircraft up to around 600-800 yards away and when I trained the system on gokarts circulating around the neighboring kart-track, I was getting good readings right down the back-straightaway (about 150 yards away).

Listening to the attached speaker, I could hear the doppler shift from people walking around in the pit-area, about 120 yards away.

So far this is a *great* success, offering far more range and sensitivity than I'd expected from a simple 8mW module -- mind you, I did spend *quite* some time tuning the amp for optimum band-pass and minimal noise.

The next step is to dump the Mattel logic board, it's limited to a maximum of 100MPH. I'll use a PIC-based board to do the same thing but the bandpass of the preamp is sufficient to allow speeds up to 300MPH to be measured so I'll code the logic accordingly.

If anyones interested in building one of these just say so and, once I've finished the thing, I'll post the circuit, firmware and PCB layouts on my website.

I'll try to attach some pictures of the rather "thrown together" prototype circuitry and microwave hardware for you to see.

[Acetronics]

Have a look to Silicon Chip ( Australian ...) issues ...

There's what you're looking for ...

Alain

Here : for the lazy ones ...

http://www.siliconchip.com.au/cms/A_107875/article.html

[XJet]

That's also a pretty low-powered unit which has been around (in various forms) for a few years now. I looked at that design a while back and it doesn't seem to have enough sensitivity to reliably clock models at anything more than 30-40 feet or so. It's really pretty similar to the Mattel unit in its design.

[hul]

I'm sure the DS guys ( http://www.rcgroups.com/forums/forumdisplay.php?f=126 ) would be interested in a unit that can measure more than 300mph. They ran out of range on their guns.

Hans

[rick.benjamin]

Ramsey Electronics kit
http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=SG7

[HobbyCNC]

Ramsey Electronics kit
http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=SG7

99MPH limit with 2 digit display? Any way to hack it to increase the display spedd. Maybe a 4X multiplier?

The dynamic soaring guys would LOVE a unit that would go as high as 350MPH!

Dave

[D.S.]

I'm sure the DS guys ( http://www.rcgroups.com/forums/forumdisplay.php?f=126 ) would be interested in a unit that can measure more than 300mph. They ran out of range on their guns.

Hans
Yes we would love to get our hands on a 350 mph + radar gun, even if we have to make it ourselves!! Currently many of us are using the Stalker Pro (http://www.stalkerradar.com/sports_pro.shtml) gun which tops out at 302. The Stalker is cool because it has a twin horn design which offers many advantages over a single horn arrangement. Even so, at the speeds our planes are traveling and with the very small frontal area presented toward the gun for such a short time we don't always get a good reading on every pass. One of the tech guys at Stalker told me that only a software change would have to be made to the Stalker Pro to allow it to measure speeds greater than the current 302 limit, but the software guys at the company are to busy to take on the job even though they are aware that there are a number of people who are requesting this. If anybody knows anyone who could possibly make the software change to the Stalker gun or build a 350 mph + gun that could reliably pick up our planes PLEASE let us know over in the DS Forum. :)

Thanks

Dean

[XJet]

You're right that a small radar profile is the biggest problem with model aircraft and speed guns. This is particularly bad when you're trying to measure high speeds because the craft remains "in range" for shorter and shorter times as the speed increases.

Unless you have the sensitivity to pick up the reflected signal at a reasonable distance then changing the software won't do much -- because the sample period will be so short as to not allow a reasonable sample to be take for anything like accurate results.

One thing I'm going to experiment with is the idea of placing small dipoles (nothing more than 3cm-long bits of adhesive metalic tape) along the leading edge of a model to see if that will significantly increase its radar profile (it should).

I've done some more work this weekend on the analog side of things to try and squeeze more sensitivity/range out of the doppler module and pre-amp setup I've already built. It's working pretty well but I notice that the mixer diode is pretty heavily saturated/biased by the gunn diode -- since they're both in the same resonant cavity. This effectively reduces the sensitivity of the whole thing quite a bit and raises the noise level somewhat.

I'm going to try a twi-horn setup next, using a controlled amount of leakage from the gunn diode source to the mixer in an attempt to improve the S/N ratio and sensitivity of the receiver side.

I did work with microwave stuff (designing doppler-based alarm and speed-measuring systems) back in the mid-late 1970s and this project is a bit of a nostalgia trip at present :-)

[D.S.]

A friend of mine has just installed a small three side corner reflector in the nose of his Destiny. A corner reflector like this one was recommended to us by the guys at Stalker as the best choice for reflecting the greatest amount of signal energy back at the gun given the size and configuration constraints of our planes. We are all looking forward to the next big day of wind so we can test it out. There are relatively few people out there who are likely to push past 302 in the near future, but it will happen and as planes and pilots get faster our current crop of radar guns are going to prevent the posting of the true accomplishments of these remarkably gifted builders and flyers.

Dean

Here's the quick build thread of the Destiny with the corner reflector in the nose:
http://www.rcgroups.com/forums/showpost.php?p=6565615&postcount=22

http://static.rcgroups.com/forums/attachments/6/6/0/7/3/a1101057-157-des5.jpg

http://static.rcgroups.com/forums/attachments/6/6/0/7/3/a1101059-223-des6.jpg

http://static.rcgroups.com/forums/attachments/6/6/0/7/3/a1101063-185-des8.jpg

[dusty IV]

What I want is a xmitter in my car that will trick speeders in thinking a Cop is on them.

I love it when they lock up their wheels. :D

[AndyOne]

Dean,

May be I'm reading your picture incorrectly but shouldn't a corner reflector have internal corners not external ones to work as it should.

Andy.

[D.S.]

Your right it's an optical construsion ( ;) ) It actually does have inside corners. A friend of mine made the one in the photos above and he did however use the wrong angles. The recommended design for a corner reflector actually uses right angle triangles and he has removed that one from the plane and made another one using right angles meeting at the inside point. It should look like a single segment of this Super Reflector sold by Stalker.

http://www.stalkerradar.com/sports_reflect.shtml

Dean

http://www.stalkerradar.com/images/reflector-a.jpg

[AndyOne]

But, the one in your picture doesn't have right angles it looks more like 60 degrees!


Andy.

[FenceMagnet]

"...he did however use the wrong angles..."

read much ?

:cool:

[richard tunstal]

miiaaaooowwwww!!!
lets not get catty ---it's nearly xmas!

to up the sensitivity could you use the lnb from a sat dish.?

dont know how you'd inject the 'local osc' other than a piece of strategically placed tin can.

i've also seen the local(dro?) oscs output fed into the amp chain in the lnb to make a
test signal source.

[AndyOne]

It must me another optical illusion because the Stalker one doesn't look right either, it should look like this...

Andy.

[D.S.]

"...he did however use the wrong angles..."

read much ?

:cool:
Do you need a shift key for your keyboard? :rolleyes:

[D.S.]

It must me another optical illusion because the Stalker one doesn't look right either, it should look like this...

Andy.
Your corner reflector has right angle triangles just like the Stalker reflector.

Dean

[Acetronics]

Hi,

Did someone had a look to Bushnell's Velocity ref 101911 CM ...

I just saw it under 200 Euros ... say 250 Bucks !!!

Alain

[D.S.]

I had a Bushnell Speedster which sold for around the same price and it was only good for foamies at close range and low speeds. As the speeds went up the gun becomes practically useless and had much more difficulty with composite planes. I sold mine after only a couple of months for $50.00 to a friend of mine and he only kept it for a few weeks before he sold it to somebody else. We were primarily using it while dynamic soaring.

http://bushnellspeedster.com/

Dean

[Acetronics]

So, might be (!) the problem is aboard the plane ...

and trying to use more reflective material/shapes.

Alain

[alwhyte_eng]

I am interested to build one of this could you send me all circuits all pictures all specifications everything nessary i would like to use it to measure speed of cars to demonstrate doppler effect.
thanks
Ainsley
email at alwhyte_eng@hotmail.com


A few months ago I bought one of those cheap Mattel HotWheels radar guns to see if it would be any good for clocking the speed of model airplanes.

Unfortunately they're not. The microwave source is *very* low-powered and the antenna system quite fundemental -- which results in a range of around 30 feet or less when used with something that has the radar profile of a typical RC model airplane.

So I set about designing and building something better.

Google was not my friend -- I could find no other DIY radar guns on the Net so here's what I've come up with so far.

I'm using a 20dB waveguide horn coupled to a gunn diode X-band module (about 8mW output power).

This module also has a mixer diode so it's easy to extract the difference between the transmitted and received signals (the doppler shift).

I've used a two-stage J-FET op-amp based low-noise amplifier to boost the signal from the mixer and (for the time being) I'm then feeding that into the logic board I ripped from the Mattel unit.

Today I tested the setup out at the local airfield. I could reliably measure the speed of full-sized aircraft up to around 600-800 yards away and when I trained the system on gokarts circulating around the neighboring kart-track, I was getting good readings right down the back-straightaway (about 150 yards away).

Listening to the attached speaker, I could hear the doppler shift from people walking around in the pit-area, about 120 yards away.

So far this is a *great* success, offering far more range and sensitivity than I'd expected from a simple 8mW module -- mind you, I did spend *quite* some time tuning the amp for optimum band-pass and minimal noise.

The next step is to dump the Mattel logic board, it's limited to a maximum of 100MPH. I'll use a PIC-based board to do the same thing but the bandpass of the preamp is sufficient to allow speeds up to 300MPH to be measured so I'll code the logic accordingly.

If anyones interested in building one of these just say so and, once I've finished the thing, I'll post the circuit, firmware and PCB layouts on my website.

I'll try to attach some pictures of the rather "thrown together" prototype circuitry and microwave hardware for you to see.