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Adam Munich

Wed Oct 13 2010, 04:14AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

ITT I'd like you to post observations that made you say huh. Not in the "what" sense but in the "huh, I didn't expect that. Interesting..." sense.

I went fishing on Lake Erie the other day, and I bought my really old transistor AM radio. (I wanted to listen to sandy beach). Well during commercials I got bored and started scanning the band. I noticed something interesting. At 700kHz i could hear a click every time my engine fired; undoubtedly due to the ignition system. Interested, I killed the motor and scanned the rest of the band. At different frequencies I could "pick up" other boats' motors. At 1460kHz I was hearing a boat nearly half a mile away. Huh.

Now you.

Steve Conner

Wed Oct 13 2010, 09:29AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Today I visited the Ebay front page, and the "Suggestions for you" were all IGBT bricks.

Yesterday I borrowed a great big LeCroy 16GS/s digital oscilloscope for an experiment. When I turned it on, it displayed a Windows 2000 splash screen and then asked for a username and password. Not only did I not know them, but the scope doesn't even have a keyboard to type them in.

On Monday I tried out my new FPGA design, and it worked! I certainly didn't expect that

Jrz126

Wed Oct 13 2010, 12:02PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

Grenadier wrote ...

I went fishing on Lake Erie the other day, and I bought my really old transistor AM radio. (I wanted to listen to sandy beach). Well during commercials I got bored and started scanning the band. I noticed something interesting. At 700kHz i could hear a click every time my engine fired; undoubtedly due to the ignition system. Interested, I killed the motor and scanned the rest of the band. At different frequencies I could "pick up" other boats' motors. At 1460kHz I was hearing a boat nearly half a mile away. Huh.

The AC130's used this to target enemy trucks during Vietnam. (Copied from Wikipedia):
During the Vietnam era, the various AC-130 versions following the Pave Pronto modifications were equipped with a magnetic anomaly detector (MAD) system called the Black Crow (AN/ASD-5), a highly sensitive passive device with a phased-array antenna located in the left-front nose radome that could pick up localized deviations in earth's magnetic field and is normally used to detect submerged submarines. The Black Crow system on the AC-130A/E/H could accurately detect the unshielded ignition coils of North Vietnamese trucks that were hidden under the dense foliage of the jungle canopy along the Ho Chi Minh trail. It could also detect the signal from a hand-held transmitter that was used by air controllers on the ground to identify and locate specific target types. The system was slaved into the targeting computer.

803

Wed Oct 13 2010, 07:28PM

Registered Member #2807 Joined: Fri Apr 16 2010, 08:10PM
Location:
Posts: 191

I was using my antique transistor radio, and on some point on the high band, at a certain point of day, I could hear 1080 AM, note this was at like at 80 MHZ + or -

hm

Adam Munich

Wed Oct 13 2010, 08:38PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Wow, that's quite a far harmonic.

Today I was in my basement and I noticed something odd. When I moved my hand under the fluorescent bulbs which haven't been replaced in a decade (yet somehow still work), I witnessed something like the DLP rainbow effect.

I think I may know what causes it. The red phosphor is slower than the blue. It takes longer to charge and longer to "discharge". This means at the end of every half cycle the blue phosphor gives a quick flash of light, making the light blueish. Then a few milliseconds later the red phosphor emits, turning the light red.

Huh.

klugesmith

Thu Oct 14 2010, 04:22PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Grenadier wrote ...
Today I was in my basement and I noticed something odd. When I moved my hand under the fluorescent bulbs which haven't been replaced in a decade (yet somehow still work), I witnessed something like the DLP rainbow effect.

I think I may know what causes it. The red phosphor is slower than the blue. It takes longer to charge and longer to "discharge". This means at the end of every half cycle the blue phosphor gives a quick flash of light, making the light blueish. Then a few milliseconds later the red phosphor emits, turning the light red.

Huh.

Sounds like the same effect I saw in an Exploratorium display before you were born, that made me go "huh".
Visitor faced a large screen that was dimly lit in yellow, 'cause that seemed to enhance the illusion.
Visitor could point a small projector that made a pattern of three different-colored dots
in a perfect vertical line. If you swept the pattern left or right, without following it with your eyes,
the vertical alignment obviously broke because one of the colored dots was lagging.

[edit] Here's one of my favorite sights that was totally unexpected the first time.
A high-altitude jet plane was making a strong, straight contrail in a cloudless, deep blue sky.
The plane's course took it right between me and the sun, or the contrail drifted to cross the sun seconds after the plane had passed.
A long, straight -dark- line appeared in the sky, as if the linear contrail were projected ahead of the plane.

That of course was the shadow of the contrail, visible in clear air because less sunlight was scattered in the shadow plane, and viewer was in the shadow plane.
I've seen it happen a few other times, not counting common contrail shadows on cloud layers.

Steve Conner

Thu Oct 14 2010, 04:32PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

So it's actually your eyes that have different response times to different colours?

I've seen a similar illusion when looking at red 7-segment displays in a darkened room. (As I often do in my secret lab, muahaha, etc.) If you move your head quickly, the red lights seem to lag the other stuff in the room.

Bjørn

Thu Oct 14 2010, 05:37PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

The lag depends strongly on brightness. Different colours will be different brightness unless carefully calibrated. Someone developed a system for 3D video with glasses that were slightly darker on one eye, causing the brain to se a different frame from each eye.

radiotech

Thu Oct 14 2010, 07:11PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Interesting but if you want to train yourself to read flash images
find a speed reading machine, the kind with the cards and the
shutter like this one. Then you can make up some color bar
cards. And dont even think of using a computer screen.

machine

card

Erlend^SE

Thu Oct 14 2010, 09:05PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

blue is a strange color.. I have to refocus my vision to see the blue power-indicator on my computer monitor after reading the white text next to it.

I did get the idea about looking at it like that from reading something about the diffraction of different light wavelengths/colors in lenses (like in my eyes) and the "blue LED problem".

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