Follow Slashdot stories on Twitter

 



Forgot your password?
typodupeerror

Comment Re: Really? (Score 1) 492 492

I get closer to 0.5 J, but still there are about 410 pellets to the oz, so for a standard 1.125 oz load that's a maximum of 461 pellets buzzing around, getting hit (hard!) by the props.

Two of those pellets have "the kinetic energy of a 56 g tennis ball moving at 6 m/s (22 km/h)". From the standpoint of a tiny, light drone, that's a lot of energy to absorb.

Comment Re:Buy an rf jammer, become a drone collector (Score 1) 1176 1176

The whole 'water absorption' thing is mostly a myth. There is not a large absorption band at 2.4 GHz - that frequency was chosen specifically since it's in an ISM band where devices that generate and use RF for non-communications purposes are meant to live.

Comment Re:Buy an rf jammer, become a drone collector (Score 1) 1176 1176

... illegally transmitting in restricted spectrum.

2.4 GHz is some of the _least_ restricted RF spectrum, FWIW.

Too bad I can't charge for using Amateur radio - I can legally transmit up to 1500W into the antenna on that band (2300-2450 MHz) with no restriction on Effective Isotropic Radiated Power. Here's a 1.0x0.6 m somewhat paraboloid antenna that has 24 dB gain in a 10x14 degree pattern, making the EIRP 377kW. I bet that would pop the radios in that drone.

(Naturally I'd never do this - according to RF exposure limits, that setup would exceed the limits for uncontrolled human exposure out to 180 feet or so).

Comment Re:Safety (Score 1) 63 63

They may be, given the horrendous loss involved and the use of directional coupling. That 50 Watt limit is not absolute, it's more of a guideline for Amateur radio stations specifically, not all emitters. Your cell phone at < 4W is also closely regulated due to its proximity to human tissue. Please refer to the FCC RF exposure site for the full regs.

RF exposure is a function of frequency, duty cycle, distance, transmitter power, and antenna gain. I have a tiny 10mW 10GHz transmitter that couples its power via WR-90 waveguide. If my math is correct, that's 3.1 mW/cm^2 at the mouth of the waveguide - WAY over the exposure limit of 1.0 mW/cm^2 at 10 GHz for uncontrolled access.

Remember, sunburns are actually RF burns.

Comment Re:Safety (Score 1) 63 63

Magnetic fields don't hurt you

STATIC magnetic fields don't seem to hurt you. Time-varying magnetic fields most certainly can hurt you. In addition to ionizing radiation (x-rays, gamma rays) which can obviously hurt you, plain old radio waves can too:

Radiation burns can also occur with high power radio transmitters at any frequency where the body absorbs radio frequency energy and converts it to heat.[1] The U.S. Federal Communications Commission (FCC) considers 50 watts to be the lowest power above which radio stations must evaluate emission safety. Frequencies considered especially dangerous occur where the human body can become resonant, at 35 MHz, 70 MHz, 80-100 MHz, 400 MHz, and 1 GHz.[2] Exposure to microwaves of too high intensity can cause microwave burns.

%DCL-MEM-BAD, bad memory VMS-F-PDGERS, pudding between the ears

Working...