I have alot of installs with 400mw cards..sr2 and mostly nmp-8602s. i was thinking of changing some of them out to R52 as some of the APs are very close together and i wanted less noise since im only serving laptop users.
then i was thinking that maybe i actually want very powerfull TX on my end, to compensate for the very bad RX sensitvity on most laptops…where as on the MT sidei can hear to ~-93 from the laptops 20-80mW radio, on the laptop side the rx sensitivty can be ~-80-85.
am i missing something here or should i want 400mw at locations serving laptops?
Maybe just try cranking TX power down on SR2 and see what happens? You might want to set up some kind of testing range for this so as to make sure you eliminate moving bodies etc. as as uncontrolled variables.
I had an AP 130ft on a tower, 150mw, ~5ft LMR 400 and a 10.5dBi omni in testing. I had access a little over a half mile away with my Inspiron 8200 and Intel 2915abg card. Wasn’t really stable, but it was also sitting on top of my laptop bag on the passenger seat of my car. I got a 1-2Mb connection, enough to play the MP3 on a network share I was using to test with.
Keep in mind, the Intel card is suppose to be capable of 50mw transmit, but its never shown more than 30mw transmit.
I imagine I would have had a better link if I had gotten out of the car. Would have been better still with a high power PCMCIA card as the AP was receiving a -89 to -90dB signal from the laptop. With an AP sitting on top of the car with stock 2dBi antenna, 100mw, I got roughly 11mb at the same location going 55mph.
edit: for clarity, I’ve tested the sensitivity of this laptop, it works at -93dB, depending on the environment and noise level, obviously.
I’m not sure about SR2s but i know that SR5s are more sensitive , i’ve seen one get a link where a cm9 didn’t ( crap link anyway but may be on par with laptop far away to an omni )
I don’t think SR5s are reliable though.
We use 400mw to service hotel/motel using outdoor MT AP’s pointed at the building w/ 9db sector antennas. You are correct, the AP’s extra sensitivity plus 9db antenna compensates for the low output power of the laptops. But most laptop users are heavy on the download side, and light on the upload, so giving them a powerful signal increases the modulation rate with less errors, so your network is faster.
Remember also that MANY laptops do not have -93db senstivity, many times you have as low at -80db (Cisco Aironet PCMCIA for example - some people still use that stuff). Some of the cheaper Broadcom chipsets aren’t sensitive either. My old Sony Vaio P3 850 laptop has a Orinoco chipset with a low output and low sensitivity. Plus associations work better with a stronger signal.
i can say this: Recently i’ve been doing some tests on the many NMP-8602s i have serving laptop users…i lower the TX power to ~60-70mw and see how that affects things. It seems not to at all..some times it will show a small gain in RSSI or sig to noise, and the end users Bandwidth does not seem to be affected based on looking at before and after snmp graphs…ive yet to see where this has been negitive in anyway.
i still want to do some more of these power down tests as well as see the results in a few weeks when i go out to a large install of these and start swaping a few floors NMP8602s with some r52s.. and do some real tests…i’ll report back when i do that.
keep in mind what evercard, is being fed into a 17dbi 90 degree sector, a large one.
If anyone can correct me, feel free, but my AP shows I’ll have a high speed connection, but my laptop shows low, 36mb on the AP, 1mb on the laptop.
My laptop can only send at 1mb, but the AP downloads to the laptop faster. I’ve done some testing, seems to be accurate. I’ve used some bandwidth tests to show the numbers.