I don't understand your comment. Were you not following the thread? The OP wants to do a doppler measurement on model rockets to ascertain speed away from the radar.
The rocket itself is probably pretty transparent to radar, so the corner reflector should function well even while the rocket is climbing.
--Mac
I think police radar would work. Also, I think you can buy "sports radars" for measuring, for example, baseball and tennis ball speeds. I found one website where references were made to the need of baseball scouts to measure pitch speed from up to 200 feet away.
If they sell these things to baseball scouts, they probably sell them to anybody. The frequency is around 10 GHz.
They have a max speed mode, which might be useful to you. I suspect that just a tiny filament of the finest magnet wire you can find placed along the fins of a rocket would increase the RCS of the rocket enough for one of these radars to pick up the doppler on it.
Especially the police radar, since it needs to pick up cars from miles away.
--Mac
I was assuming a measurement from the front. I doubt a rocket is transparent to radar unless made from non-metal and also not made from carbon. Plus the exhaust could give a false reading. It is a plasma after all. Plus the tracking is not trivial. Either the antenna has some gain or the signal will disappear rather quickly. If it has some gain, the antenna has to track the rocket.
Rene
-- Ing.Buero R.Tschaggelar - http://www.ibrtses.com & commercial newsgroups - http://www.talkto.net
Well, according to the OP, these are model rockets made from paper. If they are NOT transparent to radar, then the radar can pick up the rocket without the reflectors. If they ARE transparent to radar, then the reflector will work. You can't have it both ways.
The exhaust worries me a bit, too. I had initially neglected it. How would it look, doppler-wise to a radar? I'm thinking that the individual gas particles are too small to scatter individually, so maybe the flame plume will just act like a single scatterer? If so, it might be good enough of a reflector all by itself. Then again, I have zero experience in this matter.
As for tracking, the operator can stand as close as is safe to the rocket, and track visually, gun-sight style.
--Mac
Mac wrote in news: snipped-for-privacy@bar.net:
Issues of exhaust aside, have you ever seen a model rocket launch? Mod- rocks and mid-powers can really scoot taking off, and are easily lost visually due to their small size. What is the typical angle of regard for a police radar? Also, what is the cost? How do you track a rocket that is not modified or specially built with some sort of mechanism to increase rcs? The whole idea behind having a small, inexpensive transmitter was that 1) no modification would be needed, 2) using appropriate antenna the receiver could be placed almost under the launch pad and would cover the area of sky the rocket was most likely to go through (large angle of regard), 3) cost - I was thinking about less than $50 for a simple xmtr/rcvr pair. Transmitter would need to be very low power and of the right frequency so as not to need FCC license. It's been an interesting discussion, but I don't think radar is the cheap/easy way to go. Maybe a big spool of kevlar thread with a counter attached. At least that way I wouldn't lose and more rockets (grin)!
-- Sooner dot boomer at gbronline dot com
Yes.
In my limited experience, it is usually possible to track them with your eyes until the flame goes out.
Haven't you been reading the thread? It may very well be possible to measure the speed of an unmodified rocket with a surplus police radar, or a used "sports" radar. I have no idea what these cost. I guess you could check ebay.
If you do have to modify the rocket, it may be as simple as taping or CA-ing a little bit of ultra-fine wire to the trailing edge of the fins.
Of the issues you mention above, I think 2 and 3 are the big ones. Modifying rocket RCS is not a big deal, in my opinion. If you put 3cm (as Rich Grise suggested) of wire on the fins, you will probably have plenty of RCS. And the exhaust plume itself may have enough RCS to measure. We don't know.
I think that, with practice, you could manually track a rocket with a gun-style radar. The reading would only be accurate if the rocket is heading away from you, but the error should be minimal as the rocket gets higher.
Maybe you could find someone who has or can borrow a handheld gun style radar and get them to come to one of your launches just to see if it works at all.
Or, if you are ready to forget about radar, maybe you should start a new thread where the idea would be a miniature 2.5 GHz CW transponder for mounting in a model rocket. It seems to me that a CW Doppler radar at 2.5 GHz might just be feasible, affordable, and legal. I think the hardest part would be fitting a 2.5 GHz antenna inside a rocket...
The other promising idea that someone mentioned was the rocket-mounted sensor pack. If you had a barometric sensor in the rocket, and you could sample its output often enough, you could use that to get reliable speed information (it would be vertical speed only, I guess). And with accelerometers, you might be able to estimate max velocity fairly accurately.
--Mac
You sure can. It could be from solid metal and yet not reflect anything, but scatter forward and sideways. No ?
Rene
In theory, it can. In reality, it won't. If stealth were that easy, they would have been using it in Viet Nam war-era aircraft.
I don't think a metal cylinder of 1 or 2 inches diameter can hide from a
10 GHz Doppler radar. If you have experience to the contrary, please do tell. ;-)--Mac
In article , Paul Hovnanian P.E. writes
Reminds me of an Idea I patented some years ago only to discover that someone filed the previous year. Now in the public domain if anyone interested: Add value to vehicle exhaust silencer/muffler by incorporating a siren/whistle to be bypassed under normal driving conditions but introduced when required as an anti-theft system.
1 or 2 horsepower dedicated to generating acoustic energy with 80% efficiency as is possible with sirens would render a vehicle a centre of attention and undriveable except by the deaf....:)-- ddwyer
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