dbg@ihldt.UUCP (06/14/83)
An interesting question.. I've often found myself unconsciously trying to "damp out" the stop and go of clogged traffic. I dislike it even in my automatic. When the car in front of me jack-rabbits I coast. I know I'll be catching him soon enough -- the game is to never have to brake. Does anybody mind my doing this? ihldt!dbg p.s. It really does exist. I have the add right here in front of me. It's a radar jammer that lets you dial in the speed you want to appear to be going. Construction plans for $19.95. (I once ordered something that sounded "too good to be true". It wasn't and I was mail-order frauded ...just an unrelated story) It's in the back of July MT right underneath the 200 mpg carburator add.
chris@umcp-cs.UUCP (06/15/83)
Yes! Smooth out that traffic flow! I'll bet if you avoid using your
brakes you can save 15-20% in gas alone.
Speaking of radar jammers, I once built one. You see, it's very easy.
The hardest part is to get a K or X band Gunn diode. But the circuit
is quite simple: you need only put out little pips of current at mph
times beat frequency, where beat frequency depends on the radar band (I
think, let me see... no, it doesn't! Or does it? Oh forget it).
Anyway, it's around 30 Hz I think. If you can find someone with a
radar gun you can calibrate that way.
All you need is a 555 timer, in the astable mode. The diagram for the
555 oscillator circuit can be found in any elementary book; ask your
local Radio Shack, they probably have it somewhere. You run it off the
car battery, and use it to power the Gunn diode. Just pulse the Gunn
at the right frequency, use a microwave horn antenna mounted facing
whichever direction you prefer, and you're all set. The pulses are
much stronger than the reflected wave from the radar gun, and it
misinterprets them as the reflection beat. Turn your little
potentiometer and dial-a-speed!
Just don't get caught: the FCC gets EXTREMELY upset. The funny thing
is, all the police have to do to see if you've got a radar jammer is
get a radar detector. Pretty stupid of them not to. (Then again maybe
they do have them by now.)
Have fun kit-building! The only difficult part is the microwave horn.
Those things are tricky.
- Chris ({seismo,allegra}!umcp-cs!chris)dmmartindale@watcgl.UUCP (Dave Martindale) (06/15/83)
I often try to damp out oscillations in traffic, although you can't afford to get TOO far behind the car ahead or someone from an adjacent lane will barge into the gap, figuring that your lane is going faster. I've occasionally noticed someone in front of me trying to smooth out the speed variations, and I appreciate it. It makes it easier on me, and means that if someone up ahead has a fender-bender, that extra-large gap between cars means that all of us behind the person damping the oscillations have a better chance of not being involved in a chain collision.
rcf@qumix.UUCP (06/18/83)
My own experience is that, except in the heaviest traffic, it is easier to maintain an interval than you might think, and the "people darting in" is often an excuse used by those who like to read the fine print on bumper stickers.
martin@auvax.UUCP (06/20/83)
I too try to damp out the stop and go of traffic however, rather than limiting myself to freeway traffic, I also do the same thing in rush hour in the city. The phenomena you describe is well noted and seems to appear on most if not all freeways during rush hours. In Vancouver B.C. on the 401 going into the city, the traffic helicopters will report 'GHOST' traffic jams. They can see these things from the air. Apparently, the "GHOST' moves along the freeway and does not stay in the same place. However, the "GHOST" seems to remain until traffic thins out. As for the reason, I've no idea but am most curious. Don Martin Athabasca University Edmonton Alberta
berry@fortune.UUCP (06/21/83)
#R:ihldt:-167700:fortune:1500014:000:682 fortune!berry Jun 20 19:19:00 1983 Let's you appear to be going any speed you desire? Let's be serious, that requires knowing the following: How far away the radar is. When it sent that pulse we just received. How fast that radar is moving. How fast I'm really going. Not to mention having to do some very heavy mathematics to turn all this into the necessary timing information. What it all boils down to is that practically speaking I can confuse the hell out of radar but it is a complex operation to believably lie to it. Admittedly the government has devices not only to change relative speed indicated by enemy radar, but also to confuse it about locations but they are just not practical for you and I.
dave@rocksvax.UUCP (06/22/83)
You need no mathmatics, just a pulse generator running at an
appropriate frequency for the band you run on and enough power to
overcome their reflected signal. Most radars are of CW nature, that is
they transmit a signal continuously. The receiver in the radar unit is
coupled to the transmitter such that there is a mixing of the
transmitted signal, the reference, and the incoming reflection doppler
shifted in frequency. This produces 2 signals at the output of the
mixer, the sum of the 2 signals freq. (20 Ghz) and a difference
signal (audio). The radar filters out only the low frequency
component. This is a lot like listening to carriers on an SSB
receiver, a carrier off 1 Khz generates a 1 Khz tone out the receiver.
By putting in a pulse stream near within the passband of their receiver
you and make your own audio range signal, which is basically
indistinguishable from the transmitter-reflection signal. There will
be a small piece of the normal reflection signal modulating your audio
signal, but the digital limiting in the frequency counter will probably
filter out that small interference, looks like noise on the edges of
square waves.
If you run the same power as the police radar, very easy seeing most of
the Gunn diodes are the same, you can easily jam/have the radar read
anything you want. Let me note that only hams can legally send these
transmissions, as long as you identify on morse code at the appropriate
intervals and stay within our bands. K band no problem, we share that,
X band is an adjacent band, ends @ 10 Ghz, radar operates @ 10.250 Ghz
I think.
I still think the ultimate ham project is to build a moving radar, to
find out how fast that RX-7 passed my diesel Rabbit by. Of course that
"calibration" pulse generater would be fun to play with, imagine plodding
by a radar trap while their radar reads 98 MPH!!
Dave Sewhuk
Arpa: Sewhuk.HENR@PARC-MAXC
uucp: {rochester, allegra, amd70}!rocksvax!davezhahai@nbires.UUCP (06/24/83)
There are some problems with the simple "transmit the output of a tunable oscillator" approach: any difference between your Xtal and theirs should show up as a speed reading. Given the difference between the speed of light and car speeds, it should take a very small difference in frequency to do it. Also, if your frequency was right on, you would still have to take the shift caused by your movement into account. (Only weighted by half, however, since a transmitter travelling at 80mph should have approx the same shift as a reflection on something moveing 40mph). I recall seeing a suggestion some years ago (in 73 maybe?) for using a passive modulator in a shaped horn. Radar comes in, stimulates something (gunn diode?) and reflects back. Trick was to modulate it with an audio level signal while it was there - but not to generate an rf signal yourself. Said audio signal was supposed to be stronger than the frequency difference, get through the filters, and make "dial a speed" possible. I do not understand how this would work, but the author claimed to have experimented with it. I do know of a clever way which an acquaintance told me about, claiming to have tried it with the help of a police friend. I wonder if I should mention it? It is probably legal, should work, is totally passive (no RF involved). Sure, why not. Build yourself a rotating cup device, similar to an anerometer. Use well constructed corner reflectors, which can have a much bigger radar image than their size would indicate. (metal of course). A corner reflector is 3 planes all at right angles to each other - a signal comes in and reflects off all three surfaces then heads back where it came from (directed, not dispersed). You may have seen them near airports (at least military). Anyway, these reflectors have large radar images one way, small the other. Spin it at a controlled rate with a motor. (the prototype tested was spun by the wind). If it has a bigger image than your car - you can set the rate the radar sees. One problem is that if you subtract 40mph from a frontal reading (70-40=30) you will add 40mph to the rear (70+40=110!). Or vice versa, you can slow the rear reading and speed up the front. Better know which way the radar is from! Now, such a thing would be rather obvious, but I figure one could hide one in a plastic luggage rack. Not so hot for your sports car? I didn't say it was magic, just clever. Maybe adding and subtracting 50mph would do it: if the reading is vastly over the rate your car can go it might be ignored or thrown out of court. Not a game to play if you have a very fast car. Now I'm just waiting for the teardrop shaped dual rotor (one shielded from rear, one shielded from front) commercial model... Colorado like passive means of speed detection, by the way. No way to beat a plane.