Can you help me interpret this spectrum analysis noise plot?

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wrote:

One receiver's signal is another receiver's noise.
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Char Jackson wrote:

First of all two kinda noises. One is internal, the other is external. Under this two there are many different kind of noises.
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On Wed, 18 Dec 2013 09:21:54 -0700, Tony Hwang wrote:

I see what you mean.
I'm only looking at external noise (AFAIK) with these spectrum analysis runs.
These plots are all taken in a direction looking *away* from the city of San Jose. I'm pretty sure I'd get quite different results had I pointed directly at the Fairmont Plaza building!
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On Wed, 18 Dec 2013 10:07:41 -0600, Char Jackson wrote:

That's aptly shown by the fact that my WISP has two antennas facing me, one at channel 2 and the other (which is my "signal") on channel 10.
So, his channel 2 is creating noise for me, based on these spectrum analysis results yesterday.
http://farm8.staticflickr.com/7310/11427413806_21e93b109b_o.jpg
In the middle chart, you can see high signal surrounding channels 2 & 10. So, if I select channel 10, channel 2 is noise to me.
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On Wed, 18 Dec 2013 01:48:13 +0000 (UTC), Danny D'Amico

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".
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Jeff Liebermann snipped-for-privacy@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
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wrote:

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: <
http://www.learnbydestroying.com/jeffl/crud/Rocket-M2-interference.jpg
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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Jeff Liebermann snipped-for-privacy@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
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On Wed, 18 Dec 2013 09:19:56 -0800, Jeff Liebermann wrote:

Hi Jeff, Thanks for taking a closer look. I would *never* have been able to see that channel 9 interference in that chart unless you had outlined it as you did in your screenshot below:
http://www.learnbydestroying.com/jeffl/crud/Rocket-M2-interference.jpg
A site survey from that same radio doesn't show anyone on channel 9, but, of course, it can be coming from portable devices & microwaves:
http://farm6.staticflickr.com/5484/11427682854_0332590c4f_o.png
To see if that channel 9 pollution was coming from the house, I downloaded InsSSIDer freeware for Windows & Android: http://www.metageek.net/products/inssider/
Roaming the house, I could easily see my channel 1 home broadband router polluting channels 1 & 3; and I could see that 4 through 8 had "something" on them at much lower levels; but 9 seemed clear:
http://farm4.staticflickr.com/3774/11439214705_a722483f08_o.gif
The caveat here is that the radio measures things from miles away while the Inssider program only measures what the absolutely puny antenna and crippled radio on the laptop (or Android phone) can see - which is miniscule.
So, all I can tell from that is that the channel 9 interference isn't coming from *my* house! :)
PS: I didn't stretch any of the screenshots, so, if they're stretched, Flickr did it, not me. :)
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On Wed, 18 Dec 2013 09:19:56 -0800, Jeff Liebermann wrote:

I'm still amazed that you saw that, lurking inside the graphs!
You must have eyes like an eagle, because I had not seen it (until you pointed it out).
Although, for the life of me, I can't determine the *source* of that channel 9 interference since nothing inside the house or nearby seems to have a strong enough signal to register as channel 9 WiFi...
For example, here is a scan on my laptop for access points:
http://farm8.staticflickr.com/7364/11445566476_38a0cdf3b1_o.gif
Nothing is on channel 9.
Here is a scan of the access points from my radio:
http://farm6.staticflickr.com/5484/11427682854_0332590c4f_o.png
So, I do agree with you that there is a good amount of channel 9 interference; but I must conclude the source of that noise is distant (but clearly in the path of the radio).
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On Wed, 18 Dec 2013 08:59:51 -0800, Jeff Liebermann wrote:

Hi Jeff, Thanks for chiming in, as I know you're a God in the wireless forums, and, your information is especially useful since we're both on each side of the Santa Cruz mountains.
My speeds are actually OK, as shown in this speedtest, which shows 10ms, 19Mbps down, 18Mbps up, even though the antenna system spans over 20 miles until it gets to a bona-fide wire:
http://farm8.staticflickr.com/7310/11427413806_21e93b109b_o.jpg
I just want to make it faster. Whatever I do to decrease noise makes the signal that much better. Notice, at 56% and 66%, my signal quality figures aren't close to maxing out yet:
http://farm8.staticflickr.com/7419/11378789605_1226611246_o.jpg
Although, sometimes they get up into the 86% to 90% range:
http://farm4.staticflickr.com/3790/11375313475_125699bec3_o.jpg

Hmmm.... I don't have a clue as to the answer. All I know is that he had texted me how to set up my radio, and I set it up just like he had texted me to. I just looked at the settings in the radio, and I see the channel width set to 20MHz and channel shifting disabled, but I don't see where the channel is actually set.

Hmmm... I see the green "average" area to be around -90 at channel 10. Now I don't know if that's a good average or not, but, I'm beginning to think it's actually low signal strength, even though there's a radio aimed right at me on channel 10.

That's an interesting test to run. The radio & antenna are on the roof, so, I will have to climb up there to unplug it, and then climb back down, and then back up. So it will take a while. (Luckily it's something like 70 degrees outside today!)

That's interesting. It makes sense.

I think all the neighbors are on the same channel as the WISP radio, so, from that, I can see there will always be noise on that channel (since we're all using it).

Thanks Jeff for that insight. There are a couple of houses right under my signal, but a few hundred feet lower in elevation than I am. Perhaps some of their signal is bouncing to me. There are also a few to the side, and behind me, and above me, so, they're going to be the most problematic, I would think.
Thanks for the insight. I think everyone should post what they see from their radios so that we can all compare to each other.
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wrote:

Your equipment is the client, so you don't get to set the channel. The WISP sets the channel and all you can do is follow their lead.
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On Wed, 18 Dec 2013 21:50:34 -0600, Char Jackson wrote:

Thanks for clarifying that. I had poured over every page of the router setup, and I didn't see WHERE the channel was set.
I did see the channel width, and modulation, but, not the channel itself.
You explained why that is.
Thanks!
What I love about this WiFi gear is that we can connect to an access point five miles away, and it works as well as if the access point was in the next bedroom over!
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On Wed, 18 Dec 2013 01:48:13 +0000, Danny D'Amico wrote:

I found a good description of the three (actually four) plots here: http://wiki.ubnt.com/Best_channel_using_airview
The Waterfall chart is a time-based graph showing the aggregate energy collected over time for each frequency, where colder colors indicate lower energy levels & warmer colors mean higher energy levels at that frequency bin.
My Waterfall chart shows relatively cool colors (low energy) over all the bands except those surrounding 802.,11n channel 2 & 10, which are the two channels of the WISP antennas facing me:
http://farm8.staticflickr.com/7299/11427414296_de48f3922e_o.jpg
The Channel Usage chart, each Wi-Fi channel is represented by a bar displaying a percentage showing the relative "crowdedness" of that specific channel. This percentage is calculated based on both the popularity and the strength of RF energy in that channel.
My Channel Usage chart shows that the channel usage is between 5% and 10% where I live. I don't know if that is a high or low number, but, it *seems* low, simply based on percentages.
In my case, the channel usage is again highest in the channels that the WISP has an antenna aimed at me, namely channel 2 and 10; but the chart also shows relatively high usage in channel 1 & 3, and in 8, 9, & 11. The lowest usage is in channels 4, 5, 6, and 7, so, I guess that's where I'd put my home broadband
http://farm8.staticflickr.com/7310/11427413806_21e93b109b_o.jpg
The middle chart in both those screenshots above is the Waveform chart. Just like the Waterfall chart, this time-based graph shows aggregate energy where the color of the energy indicates amplitude.
It also shows the signal strength humping around WiFi channels 2 and 10, which are the two antennas from my WISP facing me. Oddly, it also shows red areas in the middle bands, which makes no sense to me unless they're instantaneous and short lived bursts of energy (perhaps from cellphones or microwaves?).
The bottom chart in both those screenshots is the Real-time chart which shows what a traditional Spectrum Analyzer would display in energy (in dBm) as a function of frequency.
The blue trace is called "Max Hold" of maximum power levels across the frequency. The green trace is the average energy across frequency. And the yellow line is the real-time energy.
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