Q: What's the problem. A: It's my understanding that every dB of noise reduces the dB of signal by that amount. The less signal, the slower the Internet speeds.
Q: How much noise do you consider normal? A: I have no idea. That's why I'm asking! :) Googling, I find you "should" have about 20dB of headroom between noise & signal. My signal is about -52dBm and my noise is -88dBm, so I'm within that range, but, my signal to noise ratio is -52dBm - -88dBm = 36
Q: What's the bandwidth & noise figure of your receiver? A: Googling for the "Rocket M2 bandwidth gain specifications", I find this datasheet for a "RM2" receiver & "2G-24" 24dBi dish reflector:
Which says, on page 6: Rocket M2, Operating Frequency 2412-2462 MHz 2.4 GHz RX POWER SPECIFICATIONS llg = 1-24 Mbps => -97 dBm min +/- 2 dB 11g = 36 Mbps => -80 dBm +/- 2 dB 11g = 48 Mbps => -77 dBm +/- 2 dB 11g = 54 Mbps => -75 dBm +/- 2 dB 11n = MCS0 => -96 dBm +/- 2 dB 11n = MCS1 => -95 dBm +/- 2 dB 11n = MCS2 => -92 dBm +/- 2 dB 11n = MCS3 => -90 dBm +/- 2 dB 11n = MCS4 => -86 dBm +/- 2 dB 11n = MCS5 => -83 dBm +/- 2 dB 11n = MCS6 => -77 dBm +/- 2 dB 11n = MCS7 => -74 dBm +/- 2 dB 11n = MCS8 => -95 dBm +/- 2 dB 11n = MCS9 => -93 dBm +/- 2 dB 11n = MCS10 => -90 dBm +/- 2 dB -87 dBm +/- 2 dB 11n = MCS12 => -84 dBm +/- 2 dB 11n = MCS13 => -79 dBm +/- 2 dB 11n = MCS14 => -78 dBm +/- 2 dB 11n = MCS15 => -75 dBm +/- 2 dB
Given that my Rocket M2 is 11n MIMO, and on channel 10, I'd say the receiver sensitivity is from -88 to -92 dBm.
Hmmm... I just noticed, that this is the same (essentially) as my noise figure. But, I'm not sure what that tells me.
Rumors of my demise might be a bit premature. I'm buried in projects, work, Christmas Chrisis', ladyfriend, and trying to untrash my house, office, and vehicle. Incidentally, this is what I've been doing for "fun".
Hi, 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.
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.
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.
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).
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
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.
I never deal with volts when I'm working with the radio. I always deal in power. So, I don't know what the volts are, but, I do know this about -92dBm:
0) First, I always google "dbm to watts".
1) The first hit is always a great time-saving calculator.
3) So, -92dBm is about 631 femtoWatts (which is pretty small).
4) I don't know how to convert that to volts though.
I'm not sure if I understand the question, but, the radio operates in the 802.11n MIMO channel 10 (with vertical & horizontally polarized
NOTE: The narrow beamwidth is how the antenna gets all that gain in the first place. You can't create or destroy power, so, I'd have a wider beamwidth with a lower-gain antenna. This is a pretty high-gain antenna, so, the beam width is pretty narrow, but, since it's pointed at the WISP access point a few miles away, it doesn't have to be broad.
First things first. I'm guessing your WISP picked channel 10 and you can't change that. Is that the case?
A waterfall is just time dependent sniffing. If your WISP wasn't spraying you with wifi on channel 10 (again, my guess), you would examine the waterfall display and find the area with the least activity. Now the waterfall is useful if someone burps wifi at you, as in a telemetry application. If the band was crowded, you would pick the channel with the occasional belch of wifi rather than one that is busy all the time. [If you were doing SIGINT, you would look for patterns in the occasional wifi belch. This is knows as traffic analysis.]
My next guess is you WISP provider has a customer on channel 2 at the same location that feeds you. [It could be another WISP from a different vendor.] The WISP provider has a beam antennas at the transmitter site. One beam for you on channel 10, another beam for somebody else on channel 2. That person may live near you since you are seeing the signal, but there are no red blobs in the waterfall, so the antenna isn't pointed directly at you. [And why would it be?] Red means a strong signal. The WISP on channel 2 is only 7 db less than your signal, but channel 2 and channel 10 have no common frequencies, so nothing to worry about.
You have two neighbors on channel 3, so that would be a bad channel for you, as would any channel that overlaps channel 3. Probably the WISP installer already knew that from when the site survey was done.
I'm not really sure how they determine the noise floor. At any one time, there is somebody on a wifi channel. It might be really low RF level, but not zero. Probably the receiver makes a determination that if it can't sniff a signal, it must be noise. Not a good assumption.
At -50dBm over 3 miles, I'd call it a day and go looking for something else to fix.
It's rare to see time on the Y axis, so I see how it's time-dependent sniffing. I guess it also looks like a waterfall, since it's columnar but in layers. Blue seems to be where I'd want to be, if I wasn't constrained to be on channel 10, which is my access point channel.
You are correct. The same WISP is feeding two different neighborhoods with two antennas, both at the same mast, one on channel 2 and the other on channel 10.
I can now see the waterfall is yellow'er on those two channels, as are the power levels bluer, and the real-time view greener.
You figured out a lot from that waterfall graph that I hadn't mentioned (because I didn't realize it might be relevant). Yes, the WISP is on both channel 2 and 10, and both antennas are on the same tower; but only one (channel 10) is meant for me to connect to.
The point is duly noted to stay away from channel 3. h
I think anything the antenna sees which is not a connection signal, is considered noise.
You have a point that the -50dBm isn't bad for a distance of 3 miles. I was more worried about the -88dBm of noise, but, now, after looking further, I think that the noise level is just about at the receiver
The main figure that worries me is the instantaneous noise of -40dBm. Do you know what effect this instantaneous noise might have on the radio?