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. > > One of the biggest factors of reducing the range is the obstacles in > the path of transmission... these obstacles absorb (eg. non-metallic > objects) and reflect radio waves (eg. metallic objects).. > > another thing.. even if there are no obstacles at a longer distance.. > you need a higher antenna because of earth's curvature .. this will > give you a better line of sight... yep, to give clearance for fresnel zone. remember though you need high clearance for lower freq. 2.4 ghz systems require higher towers because of bigger fresnel radius. > furthermore, regarding to low frequency versus high frequency... lower > frequencies have a greater penetration power than to a higher > frequencies for non-metallic object.. both degrade its signal based on > the density of that non-metallic object... there is also what you call, "knife-edge effect". heheh (in practise no one does this) > > for a metallic object... although it reflects the signal for both high > and low frequencies... if there is a hole in it.. higher frequencies > can pass to that hole as long as its wavelength fits to that hole... > higher frequencies have a shorter wavelength than lower frequencies... > but longer wavelengths travel greater distance than a shorter > wavelengths given on the same power output (watts)... > > fooler. > _________________________________________________ > Philippine Linux Users' Group (PLUG) Mailing List > http://lists.linux.org.ph/mailman/listinfo/plug > Searchable Archives: http://archives.free.net.ph > _________________________________________________ Philippine Linux Users' Group (PLUG) Mailing List http://lists.linux.org.ph/mailman/listinfo/plug Searchable Archives: http://archives.free.net.ph
