Can you help me interpret this spectrum analysis noise plot?

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On Thu, 19 Dec 2013 11:37:31 -0700, Tony Hwang wrote:

Save that forever!
I still have some 8" floppy disks!
My kids were amazed.
I'm saving them for the grandkids, but, they never saw so-called (hard sided) floppies ... so it might not make as much an impact on them.
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On Thu, 19 Dec 2013 11:45:23 -0600, The Daring Dufas

Mine is a Post Versalog. I still have it, as well as the HP-45 that had its 40th birthday last month. ;-)
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On 12/19/2013 3:50 PM, snipped-for-privacy@attt.bizz wrote:

Oh man, the HP-45 cost as much back then as a desktop computer costs now. ^_^
TDD
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On Thu, 19 Dec 2013 21:58:05 -0600, The Daring Dufas

The HP-45 was $395 in 1973 but very different dollars. About 50x different, for me.
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On 12/19/2013 10:34 PM, snipped-for-privacy@attt.bizz wrote:

That was a heck of a lot of money for me in those days considering minimum wage was $1.60/hr and I was paying 22 cents a gallon for regular at the San-Ann gas station. In 1971 I was working at a defense plant that made some munitions parts for the military and I was paid $1.68/hr because I was working 11pm to 7am. The 8 cents was called a shift differential paid to those who worked the night shift. ^_^
The pot's been boiling for a long time and the frogs still haven't jumped out. o_O
TDD
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On Fri, 20 Dec 2013 00:59:25 -0600, The Daring Dufas

It was my senior year in college. The minimum wage was $2.00/hr and I only worked 20hrs/wk (all they would give me during the school year). It's a good thing a glass of beer was only $.25. ;-)

They're gettin' antsy, though.
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On Thu, 19 Dec 2013 12:13:37 -0500, snipped-for-privacy@attt.bizz wrote:

Ditto. Despite the briefcase analog computer contrivance, the grunt work was done with a 6" K&E. <http://www.LearnByDestroying.com/jeffl/pics/slide-rule/slides/slide-rule.html The one in the photo is what I used a half century ago. (Hmm... why am I suddenly feeling old?) I still use a slide rule for doing gear ratios. I also give occasional demos of the slide rule to kids that have never seen one. Incidentally, I give a song and dance on using a nautical sextant in a few minutes... oops, I'm late.
--
Jeff Liebermann snipped-for-privacy@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
  Click to see the full signature.
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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
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On Tue, 17 Dec 2013 18:42:50 -0800, makolber wrote:

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: http://www.balticnetworks.com/docs/rm_ds_web.pdf 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 <=== this is my channel 11n = MCS11 => -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.
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Danny D'Amico 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?
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On Tue, 17 Dec 2013 21:19:40 -0700, Tony Hwang wrote:

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/power/dBm_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+24RdBm! 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/power/Watt_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/7299/11427414296_de48f3922e_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 929
Antenna (Ubiquiti Rocketdish RD-2G-24): http://dl.ubnt.com/datasheets/rocketdish/rd_ds_web.pdf
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Danny D'Amico wrote:

When you talk about noise there are many different kinda noise.
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On Wed, 18 Dec 2013 00:21:46 -0700, Tony Hwang wrote:

In the case here, it's all 2.4GHz signals which are not coming from the access point that I'm connecting to, yet, which the rooftop antenna sees.
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On 12/18/2013 12:12 AM, Danny D'Amico wrote:

generated noise?
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On Wed, 18 Dec 2013 01:51:40 -0800, mike wrote:

They do sell RF Armor for the Rocketdish, but, it's prohibitively expensive: http://www.rfarmor.com/cart/index.php?main_page=index&cPath=1
I guess I could fabricate the RF Armor out of steel sheathing.
http://www.youtube.com/watch?feature=player_detailpage&v=frPMnc1rW_o#tX

That would make it a neat home-repair project!
http://www.youtube.com/watch?feature=player_detailpage&v=pn7ev2NnXr0#t8

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On Wed, 18 Dec 2013 18:51:01 -0800, miso wrote:

Huh? Wow. I had never heard of that, for antennas & reflectors. Hmmm... I've seen it on the inside of monitors I've disassembled, especially the white ones (where the inside is a scratchy gray painted color).
Hmmmmm..... so what would I paint?
I guess I'd paint the backside of the Rocketdish reflector. Would I also paint the outside of the Rocket M2 radio unit? I guess I could also paint the CAT5 cable coming into the rocket.
Oooops. I just realized, I did NOT use shielded cable for my cat5. I used indoor plenum stuff. I wonder if shielded cable would have made a difference?
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On Tue, 17 Dec 2013 21:19:40 -0700, Tony Hwang wrote:

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 http://www.rapidtables.com/convert/power/dBm_to_Watt.htm . 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.
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On Wed, 18 Dec 2013 05:10:15 +0000, Danny D'Amico wrote:

I didn't explain that one all too well.
Here's another try at my thought process:
1. If I put the legal limit of 4 Watts into an antenna with a wide radiation pattern, it goes only so far. 2. 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.
1. TOA means Tangent is equal to the Opposite over the Adjacent. 2. So the Adjacent times the tangent is the Opposite. 3. 3 miles time the tangent of 2.5° is what I need to know. 4. Googling for "tangent calculator", again I take the first hit. 5. That's http://www.rapidtables.com/calc/math/Tan_Calculator.htm . 6. The tangent of 2.5° = 0.04366094 . 7. So 3 miles x 0.04 is about 633 feet. 8. The 2.5° was half the beamwidth (to make a right triangle). 9. So the beam paints a pattern twice that, at about 1200 feet. 10. 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:
http://farm3.staticflickr.com/2890/11430271156_9d854acbb9_o.png
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:
http://farm4.staticflickr.com/3743/11399640063_f0187217bd_o.png
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.
REFERENCE: http://dl.ubnt.com/datasheets/rocketdish/rd_ds_web.pdf
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On Wed, 18 Dec 2013 03:44:39 +0000, Danny D'Amico wrote:

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 just don't know. Do you?
http://farm8.staticflickr.com/7299/11427414296_de48f3922e_o.jpg
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On Tue, 17 Dec 2013 22:40:14 -0800, miso wrote:

Yes.
http://farm8.staticflickr.com/7299/11427414296_de48f3922e_o.jpg

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?
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