On Tue, Feb 9, 2010 at 2:55 PM, John Homer H Alvero <[email protected]> wrote: > On Tue, Feb 9, 2010 at 12:10 PM, fooler mail <[email protected]> wrote: >> On Mon, Feb 8, 2010 at 11:08 PM, John Homer H Alvero >> <[email protected]> wrote: >>> On Mon, Feb 8, 2010 at 10:49 PM, fooler mail <[email protected]> wrote: >>>> On Thu, Feb 4, 2010 at 12:31 PM, Junix Gaspar <[email protected]> >>>> wrote: >>>>> >>>>> I wonder whats the proximity for a jammer... >>>> >>>> depends on the wattage and the height of its jamming device... >>>> >>>> the higher the wattage .. the longer its range... but you dont need to >>>> have a high wattage jamming device if you have a clear line of sight >>>> to your target... thats why external antennas such as cellsites, >>>> AM/FM/TV transmitter needs a higher structure... >>> >>> signal diminishes with distance, think of "free space loss". so yes, >>> distance is also a factor. the lower the MHZ, the more resilient it is >>> to LOS. 2.4ghz can penetrate more obstacle than 5.4. that is why >>> 900mhz systems are often dubbed as (non|near)-line-of-sight wireless. >> >> hi, >> >> it only needs 1 watt of power for Apollo astronauts to communicate >> from the moon to earth... > > 1W is already 30dbm, by current standards 1W is already high-power. if > the Apollo astronauts where able to communicate at 1W over that > distance: > > 1. they must have used huge antennas > 2. they are transmitting at low speed > > there is also another factor: Receive Sensitivity, every radio device > has corresponding receive sensitivity, it goes something like: > > -74dbm @ 54mbps > -78dbm @ 38mbps > .. > .. > -84db @ 1mbps > > the lower the sensitivity, the better. > > you may not need high powered radios for low transmission links. but > in data wireless networks there is also what is called "fade margin". > it's just short of saying "allowance" for signal drops.
apollo lunar module used S-band frequency (2282.5 megahertz for transmission and 2101.8 megahertz for reception) for voice, data and TV transmission... it uses a 26-inch-diameter parabolic dish with a nominal power output of 0.75 watt (0.5 watt for low and 1.0 watt for high).. as long as there are no obstacles in the path of transmission and you have a clear line of sight... your transmission can go longer... this is due to induction process... magnetic field created by the antenna induces an electric field in space... this electrifc field in turn induces another magnectic field in space.. and so on and so forth... fooler. _________________________________________________ Philippine Linux Users' Group (PLUG) Mailing List http://lists.linux.org.ph/mailman/listinfo/plug Searchable Archives: http://archives.free.net.ph
