On Tue, 17 Dec 2013 21:19:40 -0700, Tony Hwang wrote:

First do you understand what decibel means in the context of voltage,
current or power? Can you calcualte receiver sensitivity of -92dbm
comes out (?) volts? On what modulation mode are we talking about?

I (think I) do understand decibels, at least at a rudimentary level.
Here's my simple summary of how I organize my thoughts around decibels:

1) Every 3 decibels is a doubling (or halving) of power.
2) A halving of power would be if it went from -87dBm to -90dBm.
3) My radio is transmits at 27 decibels (compared to the mW reference).
4) When I want to convert dBm to Watts, I google "dbm to watts".
5) The first hit is always the best dbm-to-Watts converter.
6) http://www.rapidtables.com/convert/p...Bm_to_Watt.htm
7) So, 27 dBm is 1/2 Watt (Note: 30 dBm would be 1 Watt, & so on).
8) The receiver is sensitive to -90dBm at 802.11n channel 10.
9) That means it can pick up a signal strength of 1 picowatt.
10) The signal to noise headroom needs to be around 20dBm.
11) That means I need signal to be 1/10 Watt greater than noise.
12) The transmitter is claimed to be 28dBm±2dB at channel 10.
13) So, the transmitter (without antenna) is 6/10ths of a Watt.
14) However, the Rocketdish reflector & antenna add another 24dBi.
15) A dBi is relative to a fictional spherical-radiation pattern.
16) So, my effective isotropic radiated power is 28+24=52dBm!
17) An EIRP of 52 dBm is a whopping 158 Watts!
18) The FCC only allows me an effective power of 4 Watts
19) Googling for "watts to dbm", the first link is the best.
20) http://www.rapidtables.com/convert/p...att_to_dBm.htm
21) That 4 Watts is 36dBm
22) Even though the equipment is capable of 52dBm, it's toned
down to that legal limit of 36dBm.

So, given all that, my average noise is rather low, on channel 10,
of about -90dBm or 1 picoWatt (which is the green part of the bottom
graph below).
http://farm8.staticflickr.com/7299/1...48f3922e_o.jpg

However, my instantaneous noise is rather high, at -40dBm or
10 microWatts (which is the blue line in the bottom graph above).

So, I guess my question is how much will my radio be adversely affected
by 10 microWatts of instantaneous noise, when the average noise is only
1 picoWatt?

I have no experience with what noise levels are good, and which ones
are bad - so I have no background to interpret the spectrum analysis.

REFERENCE:
Transceiver datasheet (Ubiquiti Rocket M2):
https://www.discomp.cz/img.asp?attid=88929

Antenna (Ubiquiti Rocketdish RD-2G-24):
http://dl.ubnt.com/datasheets/rocketdish/rd_ds_web.pdf