So what's the problem? How much noise would you consider normal? Thermal noise is -174 dBm per Hz What's the bandwidth and noise figure of your receiver? Mark
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:
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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?
Googling, I can make a guess that my transient noise (blue line) is very high at channel 10 of -40dBm, but that my average noise (green line) is very very low at -90dBm.
The receiver sensitivity that someone asked me to look up is at about my average noise level, at -90dBm ± 2dB for 802.11n signals.
So, the question I ask, without having the experience to know what "good" transient noise and average noise levels are, is whether or not these numbers are "good" or "average" or "bad"?
Also, I have no experience whether a peak instantaneous noise of -40dBm (which is admittedly high) has any detrimental effect on my radio performance (even as the average seems very low, at -90dBm).
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)
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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)
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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).
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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.
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.
2) That's
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.
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 antennas) that have a 3.8° to 6.8° beamwidth (which is pretty narrow).
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.
If I put the legal limit of 4 Watts into an antenna with a wide radiation pattern, it goes only so far.
If I then change the antenna pattern to be more narrow, the radiated signal goes farther in the direction that it is pointed.
So, my antenna & dish reflector, having a gain of 24dBi, is pretty narrow at around 5° beamwidth (in both horizontal & vertical planes).
Breaking out my trig (SOH, CAH, TOA), I see that I can create a right triangle of half the 5° beamwidth, with the Adjacent being 3 miles.
Since I have the angle and the Adjacent, and I want the Opposite, it looks like the tangent will tell me the how large of a circle is painted on the WISP antenna 3 miles away.
TOA means Tangent is equal to the Opposite over the Adjacent.
So the Adjacent times the tangent is the Opposite.
3 miles time the tangent of 2.5° is what I need to know.
Googling for "tangent calculator", again I take the first hit.
That's
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.
The tangent of 2.5° = 0.04366094 .
So 3 miles x 0.04 is about 633 feet.
The 2.5° was half the beamwidth (to make a right triangle).
So the beam paints a pattern twice that, at about 1200 feet.
This tells me that a beamwidth of 5° isn't really all that narrow!
Note: The 5° is defined, I think, by where the furthest lobe's power is cut in half (i.e., by 3dB).
Here is a picture of that pattern from the Rocketdish RD-2G-24:
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Notice that this radio is pretty directional, but even so, I have a catcher's mitt about 1200 feet wide to hit my access point.
Here are the Internet speeds I get by hitting that catcher's mitt:
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All I'm trying to do is *improve* on those Internet speeds, by understanding first, and then lowering my noise (or raising my signal-to-noise levels) within legal limits of 36 decibels EIRP.
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 sensitivity of -90dBm ± 2dB.
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?
Right. That's the symptom. Now, what problem are you trying to solve? Lack of speed? Variations in speed? VoIP jitter? Disconnects?
Why is your WISP using Ch 10. Is there a problem with Ch 11 or does he have his AP setup for the dreaded "auto"?
If you look at the lower graph, in the area of Ch 10, you'll see that the baseline "noise" level for Ch 10 is about -110dBm.
Unplug your antenna and see what manner of "noise" level you get. The -88dBm "noise" level is what the Rocket M2 hears between bursts of RF, when there's presumably nothing to hear. With an all digital receiver, the Rocket M2 is going to hear about 25 MHz or more of RF spectrum. I put "noise" in quotes because it's not really noise in the sense of measuring receiver NF (-174dBm/Hz). My guess(tm) is that it's mostly other users on Ch 10. That could be other client radios, such as your neighbors talking to the same WISP on Ch 10 or the 2-3 adjacent channels. It could also be additional WISP access points on Ch 10. I know you have a rather directional antenna, which is a big help at removing such "noise", but if you have the bad luck of having another client radio in the direction of the main lobe, or nearby to the side, you'll hear their "noise".
Duh. I didn't look at the pictures very carefully. Sorry.
Looks like you have interference from someone nearby using Ch 9. I marked the area on a copy of your screendump in red. I also took the liberty of tweaking the contrast so that the Ch 9 junk can be more easily seen: There's a 20dB signal level difference between your WISP and the interference, but that's probably enough to cause problems. It also explains the -88dBm "noise" level.
If you post any more images, please do NOT stretch the image. Just leave the aspect ratio the same as the original.
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