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what is the "best" signal?

Posted: Tue Jan 29, 2013 11:40 pm
by braidiano
When you do a new installation how do you check on the CPE when the signal from the AP is the best you can achieve?
I mean, is most important the best signal strenght or the best SNR?
Do you check the ccq value? Do you generate traffic before check the ccq? more params?

Re: what is the "best" signal?

Posted: Tue Jan 29, 2013 11:47 pm
by ste
When you do a new installation how do you check on the CPE when the signal from the AP is the best you can achieve?
I mean, is most important the best signal strenght or the best SNR?
Do you check the ccq value? Do you generate traffic before check the ccq? more params?
Do a Calculation and see if you reach the calculated signal strength.

Re: what is the "best" signal?

Posted: Wed Jan 30, 2013 2:48 am
by Lakis
When you do a new installation how do you check on the CPE when the signal from the AP is the best you can achieve?
U turn ur CPE little left than little right than up and down :) and u will find best signal position - just kidding but truly this is the way

good signal does not mean good throughput
In wireless everything is important and most of all is interference

Re: what is the "best" signal?

Posted: Wed Jan 30, 2013 7:26 am
by 0ldman
Simple but true.

Often you'll find that you have a tweak a link off of it's best signal to get around some local interference or weather causing for odd signals during temperature changes.

This is done on a case by case basis. No quick and hard rules for fixing a random issue.

Re: what is the "best" signal?

Posted: Wed Jan 30, 2013 1:06 pm
by braidiano
Hi,

thanks to all :)

I do not meant the random issue, like weather changing or random interference, but a best practice way to use when setting up my CPEs.

When you align your CPEs do look at the signal strengh only and try to get the best one? No others params? do you tune manually the tx-power or leave it at "default" ?

Re: what is the "best" signal?

Posted: Wed Jan 30, 2013 6:49 pm
by dog
SNR < 23 too low
SNR 30-40 target range
SNR > 50 too strong

That's my general rule of thumb.

Re: what is the "best" signal?

Posted: Wed Jan 30, 2013 7:36 pm
by braidiano
SNR < 23 too low
SNR 30-40 target range
SNR > 50 too strong

That's my general rule of thumb.
What do you do when the the SNR is too high? turn down the tx-power? misalign the CPE? :D

Re: what is the "best" signal?

Posted: Wed Jan 30, 2013 8:47 pm
by dog
I set a higher antenna gain than there really is.

Re: what is the "best" signal?

Posted: Thu Jan 31, 2013 1:17 am
by Lakis
well braidiano I really don't know what kind of measurement is 50 or 23 :) - I m also confused about this
SNR means something like with how much power should work ur radio to level up with noise in the area and the numbers should be something like 1:1 I m not really sure


in practice like dog said SNR 30-40 means exelente :)
and yes turning down the tx power sometimes may help

Re: what is the "best" signal?

Posted: Thu Jan 31, 2013 12:14 pm
by braidiano
well braidiano I really don't know what kind of measurement is 50 or 23 :) - I m also confused about this
SNR means something like with how much power should work ur radio to level up with noise in the area and the numbers should be something like 1:1 I m not really sure


in practice like dog said SNR 30-40 means exelente :)
and yes turning down the tx power sometimes may help
Hi Lakis

the SNR should be the ratio between the received signal strength and the noise, so it is involved in the "quality" of the received signal (maybe an expert can confirm this or not).

Re: what is the "best" signal?

Posted: Thu Jan 31, 2013 12:19 pm
by samir494
forgot the world said on best signal

keep in imind that what ever gives you more data transfer rate is best for you
even though CCQ is just below of 20 or equal to 100
:lol: :D

Re: what is the "best" signal?

Posted: Thu Jan 31, 2013 12:39 pm
by braidiano
ros_w_status1.png
is this good?! or the SNR is too high?
forgot the world said on best signal

keep in imind that what ever gives you more data transfer rate is best for you
even though CCQ is just below of 20 or equal to 100
:lol: :D
yes :D i know... but i just look for a "best practice" ..

Re: what is the "best" signal?

Posted: Thu Jan 31, 2013 1:52 pm
by samir494
it sound good,

chaneel-bandwidth is waht ?

use 20/40mhz-ht you will get more data through put

Re: what is the "best" signal?

Posted: Thu Jan 31, 2013 4:18 pm
by braidiano
the channel is 20MHz

Re: what is the "best" signal?

Posted: Fri Feb 01, 2013 5:18 am
by 0ldman
Hi,

thanks to all :)

I do not meant the random issue, like weather changing or random interference, but a best practice way to use when setting up my CPEs.

When you align your CPEs do look at the signal strengh only and try to get the best one? No others params? do you tune manually the tx-power or leave it at "default" ?
Best practice is dependent on a huge range of variables.

If you are looking for set rules you are going to run into problems.

Load up the AP while aligning, btest or download, etc, set it where the CCQ is the highest at the highest rate you can connect. Even still you are going to run across links that work fine for 9 months then get wonky when you have a random temperature change, then you have to adjust for it. If you adjust right you may have a weaker signal once it is settled but more reliable over all.

Each link is its own situation, every one of them is different.

Re: what is the "best" signal?

Posted: Sun Feb 17, 2013 1:05 pm
by hipro5
RULES:

a. Find the best signal strength you can.

b. Try to get the BEST Tx/Rx CCQ (100% is the best scenario) > when it drops below 93%, you will NOT able to get max throughput data.

c. Try to get the BEST S/N (bigger numbers are ALWAYS better) > 60dB is ideal.


GENERAL EXPLANATIONS (in "flat - undertanding - language"):


a. The best SIGNAL means that you are aligned and OK - BEWARE: In "Wi-Fi world" ("digital world"), you MUST have from -50dB and below (-60dB to - 50dB is ideal) because afterwards (in case of -40dB - for example), the receiver gets "overfilled" and produces its own "intermodulation distortions" which has finally an impact of downgrading data throughput.
Some of the best and "intelligent" (highly cost - professional) links out there, when their receiver "sees" high signal in its input (-38dB - for example), AUTOMATICALY drops down its Tx power in both ends to get approx. -51dB. Problem with some of them is that you can't alignment right, except from some of them that they have the alignment option, which drops to MANUAL and when you're done, it goes to AUTO itself. ;)

b. Tx/Rx CCQ means (in general words and not to put you in deep waters with transmitting digital signal) that your Rx signal has the quality provided from Tx and visa-versa. The BEST (ideal quality) is the 100%. This means that your signal is perfect (or almost perfect). When it drops lower than 90%, problems will start and firstly by dropping frames (data throughput). So we take care to have our Tx/Rx CCQ OVER 92%.
The digital signal is like a "table" - Starts from zero, goes up to its power, on its transmitting power MUST BE FLAT at whatever MHz bandwidth we have chosen, and when it ends, goes down.
IF the upper "line" is not FLAT (it might be like a wave or something), we encode QUALITY problems.
IF the upper "line" has side lobes higher than -35dBc (this is due to VERY high output RF power which its amplifier can't handle and it intermodulate producing errors), we encode quality problems as well.

c. IF our signal is too low, the receiver "reads" it BUT it also "reads" the noise that exist and if we have a signal of approx. -67dB (40dBuV) and our Tx is already in very high power producing its own intermodulation, we will encode problems with frame drops - data throughput.
IF we encode such a scenario, it will be wise to DROP the bandwidth (by lowering its MHz bandwidth) of our link to get a "more stable connection" (OR drop its output RF power in case that we have a good signal).

EXAMPLE for S/N with SIMPLE WORDS - "flat explanation so everyone can understand":

Let’s suppose that we have a receiver which has a -77dB sensitivity by its own.
By adding to it a dish of 30dBi gain, our Rx sensitivity goes down to -107dB.
In such a scenario, we HAVE to have a worst signal of -67dB to be 40dB over noise level and our signal to be stable - somehow - , supposenaly again that our Tx power is CLEAN from its intermodulation distortion (we have NOT pushed its output power to its limits).


By ALL of the above, we can safely say that on a Wi-Fi link we NEED:

a. SIGNAL strength from (worst case) -70dB to -50dB rage.
b. Tx/Rx CCQ (quality) from 92% and ABOVE with 100% ideal target.
c. S/N (Signal to Noise) OVER 40dB with best scenario 60dB.

By having these three ALIGNED TOGETHER, we are sure about our link.

Thank you very much,
George. :)

* shi(f)t!!!......I wrote a lot!!!........ :shock:

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