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


Forgot your password?

Comment: Re:Done without negative feedback (Score 2) 51

by dtmos (#48903215) Attached to: A Call That Made History, 100 Years Ago Today

What it loses in gain it gains in bandwidth: While the gain-bandwidth product is a constant, one may trade gain to obtain bandwidth. In addition, the bandwidth was settable by external components, rather than by the parasitic reactances inside the tube (valve) itself -- an important property given the (relatively) short lives of the tubes, and the manufacturing variations between different copies of them.

Negative feedback was very popular with vacuum-tube (valve) amplifiers of the 1930s and 1940s, for just these reasons.

Comment: Marketing opportunity (Score 2) 818

by dtmos (#48877581) Attached to: Fake Engine Noise Is the Auto Industry's Dirty Little Secret

This is a missed marketing opportunity. Car manufacturers need to expose an API so that third-party developers can provide owners with their own sounds -- sounds that respond to the state of the car.

Want a car that sounds like the Jetsons' flying car when you take off from a light? Now you can. Want your Prius to sound like an F1 Lotus? It's downloadable. Want your econobox to sound like a muscle car? We're here to serve you.

The good part is, the quieter the car is, the more effective the sounds will be, so those of us that like silence will benefit, too. It's a win-win!

Comment: Carbon film resistors (Score 1) 314

by dtmos (#48822865) Attached to: Radio Shack Reported To Be Ready for Bankruptcy Filing

you mean carbon. or metal film. I don't think you meant both

He could have. Carbon film resistors can be made to higher precision than carbon composition types, but typically are less expensive (but have more noise) than metal film types. There is nothing wrong with them, used in the correct application.

Comment: Re:Montana used to have no speed limit at all... (Score 3, Insightful) 525

by dtmos (#48497301) Attached to: Montana Lawmakers Propose 85 Mph Speed Limit On Interstates

Is it similar in the US?

It's a little more insidious in the US, because there is an informal speed buffer of something like "10% + 2mph over the limit," but it is not codified into law anywhere, at least AFAIK. In general, people are not harassed for slightly excessive speed, but if the officer doesn't like you, or is having a bad day, or is behind in his quota (excuse me, "performance guideline") for the month, he is perfectly within his authority to write you a ticket for doing 71 in a 70 zone.

Now, there are reasons for him not to do so; a rational judge would probably look critically on an officer that submitted several such citations, for example, but that would require one to contest the ticket in court, something one may be loath to do if one is far from home. A good attorney could probably make the calibration argument in front of the judge and win, but that would require not only contesting the ticket but hiring an attorney, which may cost more than paying a simple speeding ticket in the first place. One would also hope that a high rate of contested citations would reflect negatively on the performance of the officer in his performance review, but that's assuming a lot (including that there actually is a high rate of contested citations, and it's not just you).

When speeding in the US, therefore, one counts on the largesse of the officer, something not guaranteed to be available.

Comment: Re:Preferable to Rarer, Larger Quakes (Score 4, Insightful) 65

by dtmos (#48348989) Attached to: Nevada Earthquake Swarm Increases Chance of Larger Quake

Having been in all three (well, I wasn't exactly inside the tornado, but it was much too close for comfort), I agree that the earthquake is the choice of the lot -- if one has to be in one of the three.

However, if the question is, "Which would you rather live in -- an earthquake-, tornado-, or hurricane-prone area?", my answer would be the hurricane-prone area, because these days they're by far the most predictable and, therefore, escapable. I'm comforted by the fact that should one appear, I will have enough warning to be elsewhere when it hits. It's a lot harder to say that about tornadoes and earthquakes.

Comment: Unlocked? (Score 1) 150

by dtmos (#48300611) Attached to: SpaceShipTwo's Rocket Engine Did Not Cause Fatal Crash

The part I don't get is why one would unlock the feathering system at the start of the burn, well before it is expected to be used -- something that the in-flight videos apparently show. I can see that keeping the feathering system locked would be a safe thing to do before the release, but was the feathering system designed to be used while SpaceShipTwo was in powered flight? I was under the impression that it was not, so it would seem prudent to keep it locked until the burn was complete. Am I missing something?

I confess that I am reminded of Evel Knievel's abortive jump of the Snake River in his Skycycle X-2, which failed when his recovery mechanism (in this case, a drogue parachute) deployed during the first few seconds of powered flight. The design of recovery systems is a difficult problem.

Comment: Re:Microwaves and 2.4 GHz (Score 1) 122

by dtmos (#47937203) Attached to: Scientists Twist Radio Beams To Send Data At 32 Gigabits Per Second

I think the special part is that 2.4 GHz is a convenient frequency where there is a balance between a larger amount of energy being absorbed by water and a smaller amount of energy being absorbed by glass and plastic.

No, 2.4 GHz was just one of seven convenient open frequency bands when, in 1947, the FCC assigned frequencies for the industrial heating, diathermy, and other RF sources that were causing interference on communication systems. These bands were scattered from 25 MHz to 20 GHz. See p. 8 and p. 50-51 of the Thirteenth Annual Report of the FCC, and the 1947 US Frequency Allocation Proposal to the Atlantic City International Radio Conference (see pdf page 464 of this pdf file). They were collectively called the "ISM bands", because the FCC aggregated Industrial heating, Scientific uses, and Medical heating (diathermy) equipment into bands that would minimize interference to communication systems. The microwave oven (called an "electronic cooker" in the FCC report) was so new that it was explicitly mentioned, and lumped in with other "industrial" heating systems.

Comment: Re:Spiral filter, and a Tardis (Score 1) 122

by dtmos (#47934759) Attached to: Scientists Twist Radio Beams To Send Data At 32 Gigabits Per Second

So let me ask: If the multiplexing is due to "the phase relationship between the oscillations of the field at different positions", may I assume that these systems would be very sensitive to multipath interference -- especially varying multipath interference, as in mobile devices? Is that why the only demonstrations I have seen involve point-to-point links in free space (where multipath would be minimized)?

Comment: Microwaves and 2.4 GHz (Score 4, Informative) 122

by dtmos (#47934723) Attached to: Scientists Twist Radio Beams To Send Data At 32 Gigabits Per Second

2.4GHz is perfect for heating anything with a high water content, like tissue. That's why microwave ovens use it.

This is a myth. There is nothing special about 2.4 GHz as far as water is concerned. There is a mild absorption peak at 24 GHz, but nothing at 2.4.

Everybody likes a kidder, but nobody lends him money. -- Arthur Miller