radar guns

[rimshot]

I see alot of radar guns on Ebay ranging from $40.00 to $500.00 What is the difference? What is a good gun to use to measure my sailplane's speed without being too expensive?

[bjaffee]

The primary difference is range. The shorter the range, the closer the plane has to be in order to get a reading on the gun. All radar guns will only give an accurate speed when the plane is head-on to the gun. Typically what happens with the shorter range guns, like the Bushnell, is that you don't catch the plane until it is starting to turn away from the gun. This means that you'll get a speed reading that is slower then the plane is actually going.

There isn't much middle ground in the radar guns that I know of. On one hand you have the Bushnell for $150-200, and then you have much better (longer range) guns that cost $700 and up.

[Terminator]

Rimshot:
I agree with that. I have used the bushnell at my site tough to get an accurate reading if not impossible. Just p/u a Decatur from Bob Breau Soaring USA.com and used it first time today. Works well, very well I am happy with it.
Terminator

[timmig]

Terminator--- Ya just have too much time and money on your hands dontcha??? Guess I'll have to get out and DS with you to know how fast I'm goin!!!

[Terminator]

Timmig:
Never enough of both I would have to say there are only 24 hours in a day.
Live life it to the fullest.
Keep smiling and enjoy your family and friends.
Absolutely you can join in the fun.
Regards Terminator:)

[Greebe]

installing a corner reflector would drastically improve the range/sensitivity as would 1/4-1/2 wave strips of aluminum foil (need to know polarization eg Hor./Vert./Circular).

Effectively either would act as a passive antenna reflecting/reradiating the RF energy to a much better degree.

You should see how small a omnidirectional corner reflector is that'll light up a radar screen the size of a Buff ;)

[bjaffee]

My friend and I tried putting aluminum foil over the nosecone (not very scientific, I know), but it didnt really seem to have any effect on increasing the range.

How would one orient strips of aluminum foil, given that we want to bounce the radar of the front of the plane?

[Greebe]

What is the polarization of the radar set and the foil needs to be perpendicular to the oncoming wave... it must not be bent... always flat

[Greebe]

Just post up which Radar set being used and I'll figure out... have loads of free time on my hands :)

[bjaffee]

Originally posted by Greebe
What is the polarization of the radar set and the foil needs to be perpendicular to the oncoming wave... it must not be bent... always flat

Hmm...the only surfaces to place it on are the leading edge of the wing or the nose. Not bending them doesn't seem to be an option.

[Greebe]

mind you this is a function of frequency and polarization... never say never til all the facts are in ;)

What radar set?

[bjaffee]

The only radar that would really need it would be the Busnell.

[Greebe]

No problem. :)

Would have been nice if supplied with a more descript anwser like the correct spelling, a link, model #, etc...

I'll give them a call when they open in a couple three hours :)

[fatboywings]

My findings of the Bushnell.

I have had a bushnell for a while and use it on EPP 60" Gliders.

We DS regularly at around 100mph with our record at 110mph.

The bushnell has been a problem to start with when we started going around 90mph. The gun needs to be held still and the glider needs to do that part of the loop in front of the gun. Don't follow the plane with the gun. this has been our down fall till recently. I started picking up every pass without fail when holding the gun steady and not following the glider.

try it and let me know of your findings.

Thanks

Ben

[Greebe]

I contacted Bushnell this morning.. Sales is the same ol typically clueless... They couldn't verify that it was a K-Band unit operating at (quoting their FAQ... "The radar transmits 24 billion RF cycles of energy per second at the speed of light, which is 186,000 miles per second."

Ok sales doesn't know this (ie 24gHz) :rolleyes:

I did point out that it does not travel at the speed of light, as that only pertains to in a vacuum, not in a gas atmosphere, but I'm not suprised.

They transfered me to a product manager, has yet to return the call. Will try again in a few

[Greebe]

Talked to a sales... trainer (just got off the phone) Eric West... nice guy.. tis interested in DSing and all that (pointed him here :)

He's going to find out what he can from a product manager and call back

Sadly the reason for calling back (this is my third time) because the last saleman is an ignorant used car saleman arse. Claimed many things that goes against what we all know about this unit, not to mention was in direct conflict with the owners manual.

[Vince inTX.]

Greebe.

You must have been an E.W. in a past life. I was going to suggest a corner reflector a while back in another thread I was following but was unsure of needed dimensions. I have forgotten many things in the last 10 years. But not how big a chaff cloud looks on the bridge repeater for the sps-64. Same thing for the rubber duck corner reflector. I was going to propose that the gents here re-pour their nose weights with a corner reflector shape embedded in it. Then the makesure that the nosecone is not carbon fiber and is painted with a nonreflective paint. now when the plane rounds the bottom of the ds turn and is nose on to the radar.....BANG.....nice big pretty return.

Vince

EW 3 U.S.S. Marvin Shields 1989-1993

[Greebe]

I was... ECM USAF, B-52H (First time Best in 8th Airforce :)

Got a returned call from Eric West at Bushnell Friday with what I needed...

The Speedster radar gun operates @ 24gHz with a horizontal polarity.

To make a passive antenna (which will greatly enhance the reflected energy). To make all you need is to cut some AL foil in to thin strips 12.5mm long.. the length is extremely important. Laid out horizonally and spaced at intervals of 3.125mm(1/4wave), 6.25mm (1/2wave) etc (ie any multiple of the wavelength) apart with some cellophane taped to the LE lengthwise.

If a corner reflector is used it would need to be a minimum of 12.5mm on each axis... this will allow it to reflect radar from K-band ie 24gHz and up... longer each axis the lower the frequency. To mount one the best location would be within the nose. BUT the nose will also have to be invisible to radar, ie cannot be made of carbon... a glass nose would work fine.

If you guys need anymore info just ask, will be pleased to advise. :)

[danand]

Greebe,

Would it help to make the "cone" of the Bushnell radar gun larger? The guns trans/rec cone appears to be relatively diminutive compared to those of other radar guns.

Dan

[Greebe]

The 'cone' is nothing more than a shield to keep contaminates out... typically made of polystyrene or polyurethane foam.

a dish would work but then the unit would need to work backwards unless you used a waveguide or secondary reflector

[Puppy Rodeo]

I was thinking it would be fun to rent/beg/borrow a gun for our clubs next fun fly. Anyone ever try this?

PR

[Daemon]

Couple things.
It'd be interesting to see if the gold and silver metalic Monocote self adhering trim is radar reflective. Another option is *true* duct tape, which is a metalic aluminum tape with a peel off backing and super duper adhesive.

But something struck me here. You said it has horizontal polarity, and that the strips should be applied horizontally. Has anyone just tried orienting the gun to the wings? Usually the gun is held upright, and at DS speeds, the glider's wings are pretty much perpendicular to the hill at all times, which means it's no more than 20-30 degrees from perpendicular to the horizontal plane of the gun. I wonder if you'd get an improvement (without foil strips etc), by just simply rotating the gun 60 degrees to the right.

If it comes back to using strips in the wing though, the obvious next trick would be to throw some into the mold when building the wing in the first place.

ian

[Greebe]

^^^ the best solution would be a corner reflector in the nose. They're omni directional by design.

[bjaffee]

Would that just be a piece of steel bent at 90 degrees and placed so that the open "v" was pointing forward?

[Greebe]

one segment yes... just like a corner... but to fully realise my reference it would be ideally like two sideless pyramids with a common base... shaped like a diamond from all views. At the frequencies the Speedster operates at would not need to be more than a tad over 1" on any axis ie 25mm (H/W/D). The kicker is that the nose needs to be transparent to radar, ie not carbon, tho fiberglass would work a peach.

Let me add in realising this will only be shot at from the front only, so only half of the above is neccesary when it's base is oriented vertically with the four segments forward facing.

[SuddenImpact]

Ok,
can some one draw a diagram please before I start sticking Aluminium foil all over my plane in the wrong place:confused: :confused: :eek:

[Daemon]

Gotta be one of the ones shown on this page.
http://www.ussailing.org/safety/Studies/radar_reflector_test.htm
Just don't know which one.

ian

[Greebe]

An omni directional radar coner reflector is a octahedron with each corner segment is the same as a corner in a room. Each side measured from the corner outward does not need to be greater than 12.5mm, but exceeding this will not cause problems.. needs to be at least 12.5mm (ie longer the axis lower the frequency)

Trying to find a pic of exactly what I'm refering to is most problematic...

http://en.wikipedia.org/upload/f/f5/Octahedron.png

like this except that the outer walls are non exsistant.

You can also make similar trihedron shaped corner reflector...

http://www.gosti.com/Cal_Tgts/image4.jpg

which is a single segment corner reflector

if you want to go all out try making this...

http://www.ilcdover.com/SpaceInf/other/sdi.htm

:D

-Mike

[Greebe]

found it... thx Daemon

http://www.ussailing.org/safety/images/radHYE.jpg

[bjaffee]

I think getting something like that to fit in the nose would be a problem with most saiplanes, unfortunately. There's just too much stuff allready stuffed in there already.

Some planes have a nosecone that extends out a bit beyond the sub-nose. Perhaps a tiny reflector would fit there?

[Greebe]

We're talking ~1" ie 25mm dimensions for the full blown reflector. A trihedron shaped reflector would only be ~12.5mm on each leg. If that's too large then go with the other suggestion I made.

[Tuffplanes]

I've got a speedster and am definitely going to try the antenna idea. I'm going to use some aluminum tape and see how that works. I'll keep you guys posted. It would be awsome to get this cheep gun working good.

[Peter K]

We all have the batteries in front of the plane - perhaps can we use them as reflector antenna? But which configuration will increase the visibly for the radargun?

[Greebe]

That would all depend on the radar guns signal polarization. If that is known, the orientate the batteries the same way.

It's far easier & better to figure the wavelength and orient a cut piece of foil to do the same

[Tuffplanes]

First time out with the antenna installed in the tail of my U2. 5 wires (wire strands from a 18 gauge wire epoxied on and covered with solartex) 1 wavelength long and spaced at half wavelength intervals. I was alone but tried it out on a slow flyby. Picked up shot at 55mph at about 25 feet away. It occured to me this morning that I took the reading with the front cover on. Not sure if the antenna helps yet. If it does, it's not much. Need to try some more on the backside at higher speeds and with the front cover removed from the gun.

Norm
http://tuffplanes.com