wireless test

[Chewy]

conclusion:
it sucks

took a long phone extension(16') and moved dsl wireless modem/router to room with computers, wireless adapter is like a foot away from modem, download speeds immediately increased and I can still surf, response times for both are great. Before I could cap out at 150KB/s but even at 40-50KB/s
that's all the connection would do, shut down download to even open up google fast.

it's not ready for prime time

[RFBurns]

Wireless network transmitters and recievers utilize a modulation technique called "spread spectrum", which means the data transmitted and recieved is carried between one frequency point and another.

For example, it might begin at 2.4Ghz, and end at 2.7Ghz. This spread is 300Mhz wide. So the digital modulation occupies 300Mhz of bandwidth. A very wide signal!

A signal of this bandwidth would require an extremely clean, clear line of sight path between transmitter and reciever. Also, most frequencies used in wireless LAN networks are using part of the microwave radio spectrum. Microwaves love to "bounce" off of surfaces, making the signal "scatter" as it goes between the transmitter and reciever. This can cause "multi-path" to the signal, meaning by the time that signal plus the scattered reflected signals reach the reciever, the poor reciever is picking up the signal we want (main signal) and the reflected signals that bounce off the room walls, decorations, etc and the reciever is now detecting and demodulating multiples of the primary signal, and now must do alot of error correction inside the reciever. This will dramatically reduce the speed of the data because the reciever has to do "double time" work and remove unwanted multi-path reception. Multi-path causes the signal to be "echoed" creating almost ghost like duplicates. Depending on how much the primary signal is reflected back and forth between reflective surfaces, it can wreak havock on the primary signal we want to work with.

Putting the router which contains the main transmitter closer to the recievers eliminates 99 percent of the multi-path signals since the antennas are close and the chances the reciever picks up the reflections before the primary are slim.

Its similar to how voice would echo in a large room that is un-insulated. You hear not only the main signal (voice) but its multi-path signals too (echos). Not too difficult to pick out the main voice we want to hear, but imagine if it were 300 voices and we want to hear them all. 300 voices with echos for each voice will make it very difficult to understand what is being said.

Hope that kind of explains it.

[Chewy]

durn good explaination, line of sight thru solid core doors doesn't work worth a darn, and the reflection part explains a lot, my signal is bouncing off a heat and air unit also. the error correction for the modulation explains a lot.

at 150 KB/s download, IE still surfs ok, course my antennas are about 6 inches apart now.

[RFBurns]

durn good explaination, line of sight thru solid core doors doesn't work worth a darn, and the reflection part explains a lot, my signal is bouncing off a heat and air unit also. the error correction for the modulation explains a lot.

Thanks, glad the explanation helped. I hope it also helps others who are having speed problems with their networks.

Its a strange situation using low power microwave frequencies for LAN applications given the nature of microwave propegation and its unavoidable reflecting off of surfaces. There is another reaction that microwaves are affected too. It is called "temperature inversion". Meaning the microwaves will bend along its path due to varying temperatures between transmission point and reception point. Even though a typical room inside a home is not comparable to large distances that are found on microwave linked communications facilities, the effect is the same.

In a room, or across a couple of rooms in a home, the temperatures from floor level to ceiling are different. Since hot air rises and cold air is low to the floor, the low level microwave signal can be affected by this difference in temperature and bend away from its intended path. This causes further attenuation of the signal and could allow more of the multi-path signal get to the reciever first. Since multi-path is basically a delayed version of the primary signal we want, it all combines at the reception point causing the unwanted results. In this case with the network, drastic reduction in local network bandwidth reliability affecting the LAN's speed due to the reciever passing the data from the delayed signal instead of the one we want. The data becomes slowed when moved from the reciever into the nic card inside the PC. One might even experience gaps in downloads or corrupted downloads.

at 150 KB/s download, IE still surfs ok, course my antennas are about 6 inches apart now.

Indeed! There should be no line of sight problems there! RF signals in the Ghz frequency range move through the air in an unusual pattern. Again, certian surfaces or even things like those outdoor wind chimes can definately cause problems.

If someone always wonders why the cordless phone gets all noisy and drops out when stepping out the front door a few feet to grab the morning paper while on the phone with another party, only to be frustrated because the phone call got dropped, might check to see if the outdoor chimes are hanging in between themselves and the cordless phone base unit.

The small wind chimes are at the wavelength of certian frequencies, given their various short lengths. The wind chimes will resonate at a given frequency and cause what is called "hetrodyne" effect. The resonating wind chime will in effect create a duplicate signal, on the same frequency and begin to mix with the frequency making it resonate. It could also produce a sum of the two mixed frequencies and wala, a brand new, unintended signal causing interference to the next door neighbors XM reception or their Direct-TV/Dish Network tv reception occurs.

Great care is taken during engineering of these devices so as to minimize the interference and other problems. Manufcaturers put notice stickers on these wireless devices warning of possible interference from normal operations or adjacent wireless devices causing undesired results.

I knew a fella that took an old 2Ghz police radar gun and began to play with it one evening. He ended up interfereing with every persons cordless phone and wireless network systems in a 1 block radius. I think a few garage doors ended up opening in the middle of the night, causing a large surge in 911 phone calls from folks thinking someone was entering their homes through the garage. Dispite the fact that the police radar gun only has a 300 miliwatt RF power output, it is that horn assembly in the front that kicks that power level up into several watts, which the gain factor is called "ERP" or Effective Radiated Power.

It kind of reminded me of the hey day of radio interference when an enthusiastic CB or HAM radio operator would fire up that freshly built home brew linear amp and threw a kilowatt or two into a 30db gain directional antenna array kicking up that kilowatt of RF power to several kilowatts of RF power!

Imagine sitting next to a 10 bay FM antenna with an 11db gain per bay spec being fed by a 25 kilowatt transmitter! In the US, FM ERP power is capped at 100,000 watts. VHF high band for television (NTSC) is capped at 320,000 watts. AM radio is capped at 50,000 watts.

All of our cordless wireless devices (in the US) fall under the Part 15 FCC rules which state a maximum radiated power level of 1 microvolt measured 1 meter from the transmitting antenna with a combined antenna/feedline length not to exceed 10 feet. This translates into aprox 300 mW (miliwatts). Other countries have more laxed restrictions, others have even stiffer rules. This power level restriction for devices operating in the US is why the push to eliminate cell phones and the consistant "cry wolf" campaigns about how cell phones will cook your brain went to the trash can as fast as they began. Some even compared a cell phone to a microwave oven and that it could cause damage to the brain similar to how hamburger gets cooked in the microwave oven.

This not only is rediculous, but impossible. A typical microwave oven does operate in the same frequency range as a wireless LAN or cordless/cell phone, but the power level leaving the magnetron in the microwave oven is usually around 600 watts or more. A considerable amount from the 300 miliwatt power level from a cell/cordless/wireless LAN signal!

All of this I have posted here is to inform folks about the nature of wireless devices and possible scenarios for the undesired results often encountered with them. As newer devices are released with improved circuitry much of the common problems will be resolved or at the very least minimized.

Hope anyone and everyone finds this information informative and of use.

[jm1647]

Somebody in my neighborhood has a wireless setup I just piggy backed a connection on, nothing to brag about but it is free