Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?
DEAL: For $25 - Add A Second Phone Number To Your Smartphone for life! Use promo code SLASHDOT25. Also, Slashdot's Facebook page has a chat bot now. Message it for stories and more. Check out the new SourceForge HTML5 Internet speed test! ×

Comment Re:Ionospheric Skywave Propagation at HF freqs (Score 4, Informative) 159

I thought Solar UV deionized the skip layer during the day, which is why AM band signals travel farther at night?

No, solar UV ionizes the skip layer during the day down to lower altitudes, leading to refraction of AM band signals from those lower altitudes back to the ground closer to the transmitter than they would at night. At night, the ionized layer is higher, the refraction takes place at higher altitudes, so the signal hits the ground farther away.

There is another effect, too: The higher ionization during the day also leads to increased absorption (attenuation) of the AM band signals at even lower levels of the ionosphere (the D layer) than those at which they are refracted. The D layer disappears at sunset, so absorption by this cause goes away, increasing the received signal strength at distant locations.

The above behavior is for the AM broadcast band (~1 MHz). Above around 10-13 MHz, the situation reverses; during the day, these higher frequencies refract from layers at higher altitudes and suffer less from absorption (the absorption goes as an inverse square of the frequency), so they travel great distances, while at night, there is insufficient ionization to refract the signals back to ground, so they continue out into space and are lost. And above around 20-50 MHz, depending on the state of the sunspot cycle, there is insufficient ionization even during the day to refract the signals back to ground, so one has to resort to secondary mechanisms (e.g., ionization trails of meteors) for long-distance propagation.

Typically, typically. The above is a gross generalization: The effects of the ionosphere on radio waves depends on their frequency, their polarization, their direction and location relative to the geomagnetic equator, the time of day, the month of the year, the status of the sunspot cycle (solar wind), the magnitude of the Earth's magnetic field, the magnitude and direction of the magnetic field in interplanetary space, and eleventeen other factors. Radio propagation prediction software (e.g., VOACAP) deals in probabilities, not certainties.

Comment Not a "Model Rocket" (Score 1) 79

. . .at least by the definitions used by the FAA. See CFR 14, 101.22, viz.:

101.22 Definitions.

The following definitions apply to this subpart:

(a) Class 1—Model Rocket means an amateur rocket that:
                    (1) Uses no more than 125 grams (4.4 ounces) of propellant;
                    (2) Uses a slow-burning propellant;
                    (3) Is made of paper, wood, or breakable plastic;
                    (4) Contains no substantial metal parts; and
                    (5) Weighs no more than 1,500 grams (53 ounces), including the propellant.

(b) Class 2—High-Power Rocket means an amateur rocket other than a model rocket that is propelled by a motor or motors having a combined total impulse of 40,960 Newton-seconds (9,208 pound-seconds) or less.

(c) Class 3—Advanced High-Power Rocket means an amateur rocket other than a model rocket or high-power rocket.

Using these definitions, in the US the rocket is legally either a "High-Power Rocket" or an "Advanced High-Power Rocket", depending on the total impulse of the motor(s), but it is clearly not a "Model Rocket."

Comment Re:The Finest Day.... (Score 1) 185

I have very clear memories of watching the funeral on TV

I was a little older, and I have vivid memories of that, too. In my area, "Superman" (the live-action TV show) came on at 3:30 weekday afternoons, and I remember how annoyed I was one Friday to discover that it was canceled, replaced by a lot of boring people in suits talking -- and it was the same on all three channels! However, I consoled myself that tomorrow would bring Saturday morning cartoons (a staple of life for children in the US for some decades, now swept into history). Boy, was I annoyed to discover on Saturday that all the cartoons had been pre-empted, too!

IIRC it was a week or more before programming returned to normal -- an eternity for a little kid.

Comment Ho-hum. (Score 1) 245

If this latest revelation scares you, you'll go apoplectic to discover that this is SOP in IC design. Just about every IC more complicated than a 555 timer, from processors to Wi-Fi chips to you-name-it, has internal processors controlling substantially every part of their operation. It's a common technique to control every block one designs with an embedded core and a bit of code (in RAM, so that one could adjust the operation of the block after the design came back from fab by reloading RAM), making an easy-to-design programmable state machine. One ends up with a dozen or more cores in each chip design. Often there is one core programmed to run the top level of the design, controlling the warmup and warmdown procedures, reboot sequence, etc.

Move along, nothing to see here.

Comment Re: WTF? (Score 5, Informative) 760

When you make an allegation of corruption you need to back it up. Link to some source.

I'm not the OP (an AC), but for starters:
The Tampa Bay Times.

For those just tuning in, Rick Scott, Governor of the State of Florida, was previously the CEO of Columbia/HCA when it was found to have committed the largest Medicare fraud ever, up to that time ($1.7 Billion in 1997), leading to his resignation.

Slashdot Top Deals

Executive ability is deciding quickly and getting somebody else to do the work. -- John G. Pollard