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Monday, December 14, 2009

Goofs For Die Hard 4 (Live Free Or Die Hard)

  1. Factual errors: The "police radio" in McClane's NYPD car (and a few other official vehicles in the film) was actually a ham radio. It was an ADI model AR-147 FM transceiver. It was tuned to 144.330 MHz which is an amateur radio frequency in the two meter band. Except for extraordinary emergencies, that band is not used for law enforcement communication.
  2. Factual errors: The frequency seen programmed into the NYPD unmarked cruiser police radio is 144.33 mhz. That frequency is assigned by the FCC to ham radio operators.
  3. Factual errors: The CB radio frequency is 66.6 but CB radio is in the 27MHz frequency. 66.6 would be in the broadcast TV portion of the spectrum.
  4. Factual errors: Downloading 500 Terabyte of data via USB connection would take at least 100 days, but in the film it takes less than 2 days.



Sunday, December 06, 2009

FireFound And Prey - Locate Your Stolen Laptop

FireFound

FireFound is an add-on for Firefox and Fennec (mobile Firefox) that helps your find your computer (or mobile phone, in the case of Fennec) if it is lost or stolen. Every time your computer's location changes, FireFound sends a secure message to a central server with its current location. You can then log into the server and see your computer's current location.
All of the location data is encrypted, so no one can find out where your computer is without your password.
If you lose your computer, you can tell FireFound to clear your personal data (saved passwords, browsing history, etc.) if anyone starts your browser before you can retrieve it.
You can even run your own FireFound server; all of the code is open-source.

Note: All geolocation data is approximate, and should only be used as a guideline. If your computer has been stolen, do not try to retrieve it yourself - alert the police.



Download

You can download the FireFound browser add-on from Mozilla Add-ons. The next time you restart your browser, you'll be asked to choose a username and password for your account. You can use that username and password to log in at this website and view the latest locations of your computer.


Prey is a lightweight application that will help you track and find your laptop if it ever gets stolen. It works in all operating systems and not only is it Open Source but also completely free. 

 

Saturday, December 05, 2009

Basic Electronics For The New Ham Slide




Becoming ham radio operator or amateur radio operator ?
First of all, we need to know a lil bit about electrics and electronics.
Get a slide from ARRL

Between Amateur Radio Of Malaysia And United States

Technician Class License. You can get an entry level Amateur Radio Technician license by passing a 35-question multiple-choice examination. No Morse code test is required. The exam covers basic regulations, operating practices, and electronics theory, with a focus on VHF and UHF applications.
Technician Class operators are authorized to use all amateur VHF and UHF frequencies (all frequencies above 50 MHz). Technicians also may operate on the 80, 40, and 15 meter HF bands using Morse code, and on the 10 meter band using Morse code, voice, and digital modes.  No Morse code test is required.

General Class License. The General Class license offers a giant step up in operating privileges. The high-power HF privileges granted to General licensees allow for cross-country and worldwide communication.
Technicians may upgrade to General by passing a 35-question multiple-choice examination. The written exam covers intermediate regulations, operating practices, and electronics theory, with a focus on HF applications. You must successfully pass the Technician exam to be eligible to sit for the General class exam. No Morse code test is required.
In addition to the Technician privileges, General Class operators are authorized to operate on any frequency in the 160, 30, 17, 12, and 10 meter bands. They may also use significant segments of the 80, 40, 20, and 15 meter bands.

Amateur Extra Class License. The HF bands can be awfully crowded, particularly at the top of the solar cycle. Once you earn HF privileges, you may quickly yearn for more room. The Extra Class license is the answer. Extra Class licensees are authorized to operate on all frequencies allocated to the Amateur Service.
General licensees may upgrade to Extra Class by passing a 50-question multiple-choice examination. No Morse code test is required. In addition to some of the more obscure regulations, the test covers specialized operating practices, advanced electronics theory, and radio equipment design.

From http://www.arrl.org/FandES/ead/classes.html

Here in Malaysia, we need to pass 100 questions to get B license ( UHF, VHF and only 10 meter on HF ) and need to sit for CW test to get A class ( Can working on any amateur bands ).

Malaysia Boleh!

p/s: im not hating morse code, im loving it. i have my own training keyer, but sometimes we need to see on other side too. just keep moving forward.

Doppler effect




The sudden change in pitch of a car horn as a car passes by (source motion) or in the pitch of a boom box on the sidewalk as you drive by in your car (observer motion) was first explained in 1842 by Christian Doppler. His Doppler Effect is the shift in frequency and wavelength of waves which results from a source moving with respect to the medium, a receiver moving with respect to the medium, or even a moving medium.
The perceived frequency (f ´) is related to the actual frequency (f0) and the relative speeds of the source (vs), observer (vo), and the speed (v) of waves in the medium by









The choice of using the plus (+) or minus (-) sign is made according to the convention that if the source and observer are moving towards each other the perceived frequency (f ´) is higher than the actual frequency (f0). Likewise, if the source and observer are moving away from each other the perceived frequency (f ´) is lower than the actual frequency (f0). Although first discovered for sound waves, the Doppler effect holds true for all types of waves including light (and other electromagnetic waves). The Doppler effect for light waves is usually described in terms of colors rather than frequency. A red shift occurs when the source and observer are moving away from eachother, and a blue shift occurs when the source and observer are moving towards eachother. The red shift of light from remote galaxies is proof that the universe is expanding.

The animations below will illustrate this phenomena for a moving source and stationary observer.


Stationary Sound Source







The movie at left shows a stationary sound source. Sound waves are produced at a constant frequency f0, and the wavefronts propagate symmetrically away from the source at a constant speed v, which is the speed of sound in the medium. The distance between wavefronts is the wavelength. All observers will hear the same frequency, which will be equal to the actual frequency of the source. For a movie showing how circular waves can be created (in terms of particle motion and wave motion) go here.


Source moving with vsource < vsound ( Mach 0.7 )


 


In the movie at left the same sound source is radiating sound waves at a constant frequency in the same medium. However, now the sound source is moving to the right with a speed vs = 0.7 v (Mach 0.7). The wavefronts are produced with the same frequency as before. However, since the source is moving, the center of each new wavefront is now slightly displaced to the right. As a result, the wavefronts begin to bunch up on the right side (in front of) and spread further apart on the left side (behind) of the source. An observer in front of the source will hear a higher frequency f ´ > f0, and an observer behind the source will hear a lower frequency f ´ < f0.


Source moving with vsource = vsound ( Mach 1 - breaking the sound barrier )


 



Now the source is moving at the speed of sound in the medium (vs = v, or Mach 1). The speed of sound in air at sea level is about 340 m/s or about 750 mph. The wave fronts in front of the source are now all bunched up at the same point. As a result, an observer in front of the source will detect nothing until the source arrives. The pressure front will be quite intense (a shock wave), due to all the wave fronts adding together, and will not be perceived as a pitch but as a "thump" of sound as the pressure wall passes by. The figure at right shows a bullet traveling at Mach 1.01. You can see the shock wave front just ahead of the bullet. Jet pilots flying at Mach 1 report that there is a noticeable "wall" or "barrier" which must be penetrated before achieving supersonic speeds. This "wall" is due to the intense pressure front, and flying within this pressure front produces a very turbulent and bouncy ride. Chuck Yeager was the first person to break the sound barrier when he flew faster than the speed of sound in the X-1 rocket-powered aircraft on October 14, 1947. Check out the movie The Right Stuff for more about this significant milestone, and the beginnings of the US space project. The figure at right shows a n F-18 at the exact instant it goes supersonic. Click on the figure to see more information and a MPEG movie of this event.

Source moving with vsource > vsound (Mach 1.4 - supersonic)






The sound source has now broken through the sound speed barrier, and is traveling at 1.4 times the speed of sound (Mach 1.4). Since the source is moving faster than the sound waves it creates, it actually leads the advancing wavefront. The sound source will pass by a stationary observer before the observer actually hears the sound it creates. As you watch the animation, notice the clear formation of the Mach cone, the angle of which depends on the ratio of source speed to sound speed. It is this intense pressure front on the Mach cone that causes the shock wave known as a sonic boom as a supersonic aircraft passes overhead. The shock wave advances at the speed of sound v, and since it is built up from all of the combined wave fronts, the sound heard by an observer will be quite intense. A supersonic aircraft usually produces two sonic booms, one from the aircraft's nose and the other from its tail, resulting in a double thump. The figure at right shows a bullet travelling at Mach 2.45. The mach cone and shock wavefronts are very noticeable.