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hlekat
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Calculate max wireless distance.

Tue Mar 29, 2011 12:24 am

I own two mikrotik routers 411u + 433au with two r52 wireless cards (17db)

I use two panel antennas with the following specs:

product code INT-PAN-23/5X-HV
frequency 5150-5850MHz
impedance 50Ω
VSWR (max) 1.3
gain 23dBi
beamwidth (-3dB): horizontal 10°
beamwidth (-3dB): vertical 10°
front to back ratio > 35dBi
cross polarization > 24dBi


I bought them to link two location with distance 6km and 500m height differnce.

I got :
signal stregth -92
noise floor : -105
snr : 13

The tx power was 17db the maximum of the wireless card, I lowered the power to 15-12-9-3 db and the results was the same. -92 , -105 , 13 . +-1.
The two antennas failed to connect. What should I do?
If a replace the R52(17db) with R52hn (25db) in both routers would be any difference?


The frequency is 5180 mhz .

How much is the maximum distance for these antennas and wireless cards?
 
karlos
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Re: Calculate max wireless distance.

Tue Mar 29, 2011 11:44 am

on 6km link using R52 cards and 23dBi antenas ?
i would expect -63dB signal level

So if you have so low signal, ill ask why ? Are the antenas usable for this 5180MHz band ?
Did you tryed another cards (another R52) or another type of antenas?

If everything is OK the calculations are very accurate, not more that 3dB difference betweet calculated and real values
 
angboontiong
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Re: Calculate max wireless distance.

Tue Mar 29, 2011 3:13 pm

the simple way is, you have to test it in your office.
if it work then only deploy on site.

8)
 
Muqatil
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Re: Calculate max wireless distance.

Tue Mar 29, 2011 3:14 pm

Do you have LOS between the points?
Do you have the fresnel zone clear enough?
Is the Antenna Polarization the same for both sites?
Are all the cables correctly plugged in?
You have serious problems if your signals are so high..
Renato Bernardi

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hlekat
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Re: Calculate max wireless distance.

Tue Mar 29, 2011 6:54 pm

1. The polarization is the same both antennas are vertical.
2. The network has been tested in the office before going to the mountain
3. I forgot to keep the signal strength in the office
4. The antenna is made for frequencies : 5150-5850MHz
5. I assume that the cables are correct , what could be wrong if they are tight enough the antenna cable and the pigtail in the wireless card
6. I haven't tested any other equipment antennas or wifi cards. This is my first attempt in long distance wireless links.
7. If los is meaning line of sight between the two point, yes they are viewing each other without any obstacles.
8. fresnel zone i don't understand the difference with the los.

One point is in a top of a mountain. 550m altitude
The other point is near the see.

So it is very easy for them to have a los or fresnel zone.

In front of the antenna (about 15meters) in the mountain they are some power cables but they are in higher altitute by 4 to 6 meters from the antenna.

The panel i am using: http://www.linkshop.gr/shop/index.php?t ... duct_id=40
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Muqatil
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Re: Calculate max wireless distance.

Wed Mar 30, 2011 3:24 pm

http://en.wikipedia.org/wiki/Fresnel_zone
I cannot find the link calculator with Fresnel Zone calculation too, i usually use RadioMobile, but might be a PITA to configure.
If you plan to make a lot of links, RadioMobile tool is a must.
Renato Bernardi

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hlekat
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Re: Calculate max wireless distance.

Wed Mar 30, 2011 9:40 pm

I am posting some photos to have a closer look.
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Muqatil
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Re: Calculate max wireless distance.

Thu Mar 31, 2011 12:20 pm

your pics show 2 problems, fresnel related:
1 the trees @ point B are too high, you need to raise your pole at least of 3-4 meters
2 the mountain on the right side of the antenna A (from point b view) might be a problem aswell, (not sure because the point is very far away)
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hlekat
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Re: Calculate max wireless distance.

Thu Mar 31, 2011 6:59 pm

The threes ? Can they affect the signals?

See one more photo, i think that the trees should not the problem. I thought that maybe the antennas @ (1.8ghz) or the power cables might cause some problems.
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WirelessRudy
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Re: Calculate max wireless distance.

Fri Apr 01, 2011 12:42 am

the second photo with "Antenna A" show trees some hundred or so meters away. You're LOS is just overshooting these thus the trees are almost definitely in the Fresnel. The moisture (water/vapour) in the leafs consume the electromagnetic energy of the radio waves. And the surface of the leaves also reflects the energy. Trees are killers when it comes to wifi radio links....

I see another problem: transformers in the elec. poles. They can radiate high magnetic or fields or radio waves. That COULD affect your radio's too...

Is this high telcon tower really this close or is it illusion/artist impression?
Why not use this tower? Much higher and more away fm. the power transformers.
 
hlekat
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Re: Calculate max wireless distance.

Sun Apr 03, 2011 11:48 pm

the second photo with "Antenna A" show trees some hundred or so meters away. You're LOS is just overshooting these thus the trees are almost definitely in the Fresnel. The moisture (water/vapour) in the leafs consume the electromagnetic energy of the radio waves. And the surface of the leaves also reflects the energy. Trees are killers when it comes to wifi radio links....

I see another problem: transformers in the elec. poles. They can radiate high magnetic or fields or radio waves. That COULD affect your radio's too...

Is this high telcon tower really this close or is it illusion/artist impression?
Why not use this tower? Much higher and more away fm. the power transformers.

Currently one of the routers has been send to rma so I can't make any tests. I didn't know that the leaves could cause problems.
My antenna was 2 meters higher but I have cuted the flagpole for installing it easier because I was using a ladder and I was afraid the wind if I was that high.
The trees and bushes in the other picture are about 120meters far away.
The tel. tower is not mine to use it.
 
0ldman
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Re: Calculate max wireless distance.

Mon Apr 04, 2011 1:54 pm

I think you've got a hardware problem. Cables, antennas or radios.
 
hlekat
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Re: Calculate max wireless distance.

Mon Apr 04, 2011 11:27 pm

I think you've got a hardware problem. Cables, antennas or radios.
The physical conditions are suitable for better signal strength?
 
WirelessRudy
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Re: Calculate max wireless distance.

Mon Apr 04, 2011 11:47 pm

I think you've got a hardware problem. Cables, antennas or radios.
The physical conditions are suitable for better signal strength?
No. See my previous post.
Cut the trees at distant of higher your masts.
You can try to use even higher gain antenna's and more powerfull radio's but you get more signal disortion at the recieving end as bonus. So high levels but low quality.
 
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Re: Calculate max wireless distance.

Tue Apr 05, 2011 12:02 am

You are having a typical fresnel zone problem. we have 3 fresnel zones. These are 1st, 2nd and 3rd. if any obstruction encroaches into the 1st zone, you will be having signal with low SNR but the link will be working though this will have negative effect on the throughput of the link. however if the obstruction encroaches into the second fresnel zone, the SNR will be very low (as in your case) and the link will not be able to carry data AT ALL. Finally, if obstruction encroaches into the 3rd fresnel zone, then the link will not be established.

The first approach to solve your problem is to clarify that the board and cards are working very well by testing inside your lab or on the ground. at this point take note of the values and proceed to the site.

At the site, take note of the tilt angle (as i noticed that point A is higher than point B above sea level) if tilt angle cannot solve the problem, then consider increasing your height especially at the site you have lots of trees.

you can consider 900MHZ is it is unlicensed in your country.

I hope this helps.
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Re: Calculate max wireless distance.

Tue Apr 05, 2011 7:34 am

oseni, cool avatar, I think this logo is from year 2000 :)
No answer to your question? How to write posts
 
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Re: Calculate max wireless distance.

Tue Apr 05, 2011 10:38 am

very good explanation bholler!
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hlekat
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Re: Calculate max wireless distance.

Sat Apr 09, 2011 3:46 pm

Because I can't cut the trees and secondly to raise the antenna 2-3 meters higher is a little bit difficult If I replace the cheapest part in the wireless link which is the wifi card from R52 to R52 High power is it going to be better?

I have just received the router from the rma and I realized tha also the wifi card of the specific router has problem. So because I am going to buy a new one, will be better a R52 Hn instead of a R52?

my antenna is 23db.
 
WirelessRudy
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Re: Calculate max wireless distance.

Sat Apr 09, 2011 5:15 pm

Because I can't cut the trees and secondly to raise the antenna 2-3 meters higher is a little bit difficult If I replace the cheapest part in the wireless link which is the wifi card from R52 to R52 High power is it going to be better?

I have just received the router from the rma and I realized tha also the wifi card of the specific router has problem. So because I am going to buy a new one, will be better a R52 Hn instead of a R52?

my antenna is 23db.
If this would be my link and I would have ample budget than I would try the following, in that order:
1. Check that all connectors are properly fit and clean and well protected against moisture.
2. Make sure antenna and radio and board have good one common earth connection.
3. Scan on both end for which frequencies are free. Than pick one free one as high as possible but also keep as much distant to other channels as possible. Scan on 5, 10 and if possible on 40Mhz as well to see if the spectrum is not used in these ranges. Better would also to have a spectrum scanner look at it but these are very expensive.
4. Raise the height of the antenna. Even if you can gain only 1 mtr. every meter is one.... Just an extra pole on top of the other, eventually with some support wires to keep it sturdy in the wind, can't be such a big issue and is cheap.
5. Use better (higher gain) antenna. 28 or 30dBi dome antenna bundles the radiated energy more and also the direction it receives signal fm opposite site is more focussed. (http://www.interprojekt.com.pl/gold-wir ... p-376.html)
6. Use higher power radio's.

1. bears no costs
2. bears little costs
3. bears no costs at all
4. bears little to medium costs
5. bears medium (to high depending your budget) costs
6. bears little to medium costs.

Actually putting higher powered card gives you the least change of improving results in regard to have a good quality connection. Although the higher power at the other end (you have to do it on both ends) gives more signal, it also gives more multipath receipts from same radio.

One thing I also would try is to setup a 802.11n link. This will handle the tree distortion much better in my opinion. But this is something not really proven to be true on this forum so some uncertainty in that respect is there.. But you could give it a try although you need other radio cards and if you want to use both chains you also need dual polarity antenna. Now here your costs go up! (http://www.interprojekt.com.pl/jirous-j ... -1092.html)

Good luck! :)



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Re: Calculate max wireless distance.

Sun Apr 10, 2011 3:29 am

(that's a lot of bears ...)

:D
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WirelessRudy
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Re: Calculate max wireless distance.

Sun Apr 10, 2011 4:59 pm

(that's a lot of bears ...)

:D
By the hour you wrote this it seems to me you must have missed a lot of ´beers´! :D
 
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Re: Calculate max wireless distance.

Mon Apr 11, 2011 1:44 am

hi hlekat,

the best bet here is 900Mhz if you want a link that can make you sleep with all your eyes closed. However, consider increase in height and high gain antenna as wirelessrudy suggested. Changing to high powered radio wont improve your signal.

i hope this will save your time.

Regards

Abiola
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Re: Calculate max wireless distance.

Tue Apr 12, 2011 10:06 am

simple raise the height of the antennas on either sides and make sure you have a CLOS not NLOS . The hardware should be able to give the link
 
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Re: Calculate max wireless distance.

Wed Apr 13, 2011 10:51 pm

i think sometimes lowloss cables make difference, dont hesitate to try another one
 
WirelessRudy
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Re: Calculate max wireless distance.

Tue Aug 02, 2011 11:10 am

hi hlekat,

the best bet here is 900Mhz if you want a link that can make you sleep with all your eyes closed. However, consider increase in height and high gain antenna as wirelessrudy suggested. Changing to high powered radio wont improve your signal.

i hope this will save your time.

Regards

Abiola
I don't know where hlekat is located but in many countries 900Mhz is license free. In Europe it is not free yet for private businesses and if it becomes it will be licensed.
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Re: Calculate max wireless distance.

Tue Aug 02, 2011 11:11 am

hlekat, thanks!
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Re: Calculate max wireless distance.

Thu Aug 04, 2011 8:03 am

The signal to noise should not be effected by fresnal encroachment, however the integrity of the signal will most certainly be affected.

What is being refered to as the 1st fresnal is the full field or full power.
The second Fresnal is the half power or ~70% field.

Encroachment into the first freznal and upto the 2nd fresnal has minimal effect on the signal (has some effect on the signal integrity but not overly significant).

Encroachment into the second freznal has indeterminate results from bad to worse.

Avoid encroaching into the 2nd freznal if at all possible.
Poor signal integrity causes retransmits, and datarate shifting.

EDIT: One should not try to POWER their way through obstructions, you just create noise further out.
 
hlekat
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Re: Calculate max wireless distance.

Fri Sep 02, 2011 5:08 pm

I will finally raise both antennas height and i will post the results.

For a wireless link to be stable (without disconnects) I will need a signal better than -80db?
 
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Re: Calculate max wireless distance.

Sat Sep 03, 2011 1:50 am

I will finally raise both antennas height and i will post the results.

For a wireless link to be stable (without disconnects) I will need a signal better than -80db?
Depends a bit on the spectrum use and resulting background noise. As a guide line signals between -30/-40 to -70 should be looked for. Optimum is between -45 to -65, special when NV2 protocol is used.
But that doesn't mean -80 won't work. You have to play different tricks, or just be in a clean spectrum situation, to works with these signals. Is also depends what data rate you want to maintain.
If little data speed is needed only (<6Mb) you can set conn. rates very low so links will stabilize more.
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hlekat
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Re: Calculate max wireless distance.

Sat Sep 03, 2011 11:25 am

I will need bandwitdth for a 8 channel dvr. I suppose 6Mbps are more than enough. The dvr could work with less than 1Mbps with the required settings. So speed isn't the problem. I am waiting a new R52 card to test the network. So I have a couple of days before going for the raising of the antennas.

If signal is about -80db or -90db could i make any tweaks settings, like to enable a protocol from the menus? All the settings are default excepted the interface settings that are needed for the wireless.

edit: I am using 4.17 on both routers.
 
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Re: Calculate max wireless distance.

Sat Sep 03, 2011 1:50 pm

OK, if your bandwidth need is 6Mb or less than I would set the data rates at 12 or 18Mbps for 802.11a/g (also set 6mbps)
you can try to use the NV2 protocol.
You can also set the bandwidth of the channel to 10Mhz and increase the data rate to 18/24Mbps. Or even go to 5Mhz.
You have to try the several options to see which gives best results. I have very good results with remote units 7km's away that are having Fresnel issues. I set their data rates (in AP) very low, just enough for their traffic demand) and it works.
Make sure AP has client in the access list and the client has the AP in the connect-to list and remove both side the ´default authenticate´ ticker.
In case of 10 and 5Ghz channel bandwidth set the freq. of the AP in the "Scan List" of the wireless interface.

I would also upgrade to v5.6, its very stable now, special on the wireless. It also comes with the "Safe Mode" option in winbox. Meaning that you can set an alteration of the remote unit in "Safe Mode". If you would lose the connection after some time unit falls back to last settings and you have connection again.
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hlekat
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Re: Calculate max wireless distance.

Sat Sep 03, 2011 2:26 pm

If I update to 5.6 could I import the same configuration file that I am using to 4.17?
I am interested only for a stable link even if it 2-3Mbps I don't care for the bandwidth as soon i will only connect to the dvr.

5mhz channel spectrum will be more stable than 10mhz ?
Click the check boxes with the lowest bandwidth values?
Add each other to connect-list and remove default authenticate check-box
Update to 5.6 so I could use the NV2 protocol instead of Nstream?

I haven't either use the Nstream protocol in the first attempt. with the low singal values.
 
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Re: Calculate max wireless distance.

Sun Sep 04, 2011 3:20 am

If I update to 5.6 could I import the same configuration file that I am using to 4.17?
You can update a production unit just like that. The config stays for 99% in place. (The 1% is for the event it might not. But I always update my running units in the field like that.) Just upload the needed packages (copy and paste from your desktop into the winbox / files window of the unit) and reboot the router. For security you can make a back-up of the router first. It comes up in the same ´files´ window. You can copy and paste (click on it and drag it onto an empty space of your desktop) that backup file to your PC/laptop.

If you mean you have a config script to setup new units, the script language might have been changed here and there. So check things out. It depends completely on what the script has to set.
I am interested only for a stable link even if it 2-3Mbps I don't care for the bandwidth as soon i will only connect to the dvr.
Set to the lowest data rates only then. This gives the most stable link in poor conditions.
5mhz channel spectrum will be more stable than 10mhz ?
Don't know. If the channel width is smaller it means the radio energy is bundled more so penetration of the link is further or at same distance you get higher signal. But if the Fresnel actually becomes less wide with a smaller bandwidth I don't know out of my head. I know the Fresnel zones are related to the used frequencies, but what the relation is to the channel bandwidth, I need to read-in on that.
Add each other to connect-list and remove default authenticate check-box
Add the client (stations) in the access-list of the AP, and add the AP in the connect-to list of the client. Access list only carries mac addresses, the connect-list can be base on AP mac address, AP SSID or both at the same time.
You can find all that info in the Wiki or manual; http://wiki.mikrotik.com/wiki/Manual:Interface/Wireless.

Update to 5.6 so I could use the NV2 protocol instead of Nstream?
Yes, you could.
I haven't either use the Nstream protocol in the first attempt. with the low singal values.
I never used nstreme. NV2 is better anyway imho.
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Re: Calculate max wireless distance.

Sun Sep 04, 2011 10:52 am

1: Noise is a product of bandwidth.
2: The SNR forms part of the radio card's data-rate control loop.

Analogy, lets say you have a fancy sun lounge with curtains to all the windows. And that you bought some furniture that has fabric which fades in UV light.

You open all the curtains and all the light floods into the room (including the UV light, the UV fades the fabric quickly)

You open just one curtain, the light comes in, the room is not so bright, and there is a lot less UV light, the fabric fades over many months!!!

In this case, the light is the signal and the UV light is the noise!!!!

If you reduce bandwidth to say, 10Mhz or 5Mhz channel, the SNR ratio will increase (since the noise component has fallen), and since SNR is part of the control loop, the data-rate will increase. (BUT LETS NOT FORGET THAT POSSIBLE DATARATE IS A PRODUCT OF BANDWIDTH) and that the less bandwidth you have, the lower the data-rate will be.

This may sound contradictory, but what I am trying to say, is that in less than optimum condition (ie with noise), the throughput could go up with a narrower bandwidth, than with a wide bandwidth and lots of noise!!!!!!!!
 
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Re: Calculate max wireless distance.

Sun Sep 04, 2011 4:57 pm

1: Noise is a product of bandwidth.
Imho noise as we speak about in this forum is just a sum of electromagnetic waves produced by all kind of sources but of a nature we don't have any interest in apart from avoiding it.
In your analogy of the windows and curtain, the amount of absolute ´noise´ differs only because you open or close the shutters. The total amount of signal (´light´) also differs linear with it. The relative comparison between the amount of noise (´UV´) and sigal (`light`) stays the same. This S/N ratio is mentioned in decibels (dB) and it stays the same. So imho it makes no difference for a receiving antenna on what bandwidth it is listening. The S/N stays the same.

The radiowave on the other hand, transmitted by the radio with the same available energy but into a smaller (smaller amplitude of the radio wave?) bandwidth has a higher energy density and therefore at the receiver more field energy is available. Since the background noise in absolute terms stays the same, the S/N ratio increases simply because the Signal strength increases. Minimal S/N levels are needed for stable communications and when talking marginal conditions, an increase in signal due the use of a smaller bandwidth can therefore indeed improve the link quality.
Not because your curtains are more open. No, because your sun puts more energy in the visible spectrum.
2: The SNR forms part of the radio card's data-rate control loop.
True, and we just saw that the signal increased, thus the SNR (S/N).

Higher connection rates can be obtained or sustained as long as they fall within the ´sensitivity´ boundary of the radio receiver. (Most cards have less output power in the higher rates, and the sensitivity also decreases a bit. For a 6mbps conn. rate in general less signal is workable then the 54mbps.
But, since the bandwidth is halved in 10Mbps, or even quartered in 5Ghz the available data throughput also gets halved or quartered.
In marginal situations it can be that by using narrower bandwidth radio channel the overall link quality improves to such extend the final gain in throughput is bigger than the loss of theoretical data throughput due the halving or quartering of the channel.

[I've had two clients on a 20Mhz channel both getting -78 to -83 signal in the 5Ghz band and due this only 6 adn 12 Mbps conn. rates gave some connectivity where the link still dropped at times.
I altered the link to 10Mhz bandwidth and gained some 2dB-2,5dB on the signal at the clients. The links stopped dropping and the CCQ went up from a lousy 30-40% to 80-90%.
Clients were allowed to use 3Mb download and complained about poor internet and the impossibility of using skype most of the day. After the change they had good internet speeds and Skype only had occasional problems thereafter.]

what I am trying to say, is that in less than optimum condition (ie with noise), the throughput could go up with a narrower bandwidth, than with a wide bandwidth and lots of noise!!!!!!!!
I can only second this.


All this doesn't give me the answer to what the effect of the use of a narrower channel width will be in relation to the Fresnel zone of the radio link.
Fresnel zone is depending on the used frequency and the link distance, but I am not sure what its relation is to the channel width. I am trying to find some info on the internet but so far did not yet found any in relation to this question.
Anybody that might shine a light on this?
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Re: Calculate max wireless distance.

Sun Sep 04, 2011 8:56 pm

Rudy.

Trust me, noise is a product of bandwidth and it is a matter of basic engineering physics.

http://searchnetworking.techtarget.com/ ... oise-ratio

S
 
WirelessRudy
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Re: Calculate max wireless distance.

Mon Sep 05, 2011 2:25 am

Rudy.

Trust me, noise is a product of bandwidth and it is a matter of basic engineering physics.

http://searchnetworking.techtarget.com/ ... oise-ratio

S
Sorry, but I don't agree with your statement.
The bandwidth they refer to in your mentioned article in :
Communications engineers always strive to maximize the S/N ratio. Traditionally, this has been done by using the narrowest possible receiving-system bandwidth consistent with the data speed desired.
is imho something different than the bandwidth we refer to.

Bandwidth in the "receiving system" imho means the working range of a receiver circuit. Any signal outside this will theoretically not be allowed to be picked up and thus causes no ´noise´. By limiting the working ´bandwidth´ of the radio we only limit out of band noise. Not noise in the working radio band we use.

Bandwidth on the transmitted frequency we talk about here is the difference between the upper limit of the channel`s centre frequency and the lower limit. Or the amplitude of the centre frequency.
I don't see how noise can be a product of the radio wave's amplitude. Noise is there and mostly out of our management. All we can do is avoiding noise pick-up from frequencies we are not listening too.
Reducing a wave's amplitude is imho is not reducing the SNR on the receiver, specially given the fact that atheros chips are not very good in even stopping interferences from nearby channels that are in the ´system bandwidth´ of the radio.

Actually I have seen it happening. Reducing the working channel width on my AP given in my previous post has increased the signal levels received on both ends. But the average noise floor stayed just the same. Only by increasing the signal we increased the SNR and thus improved the link quality.

I really don't see how noise can be a product of the chosen bandwidth.
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Re: Calculate max wireless distance.

Mon Sep 05, 2011 2:31 pm

I am sorry you don't understand, I will wait for you to rewrite science.

S
 
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Re: Calculate max wireless distance.

Mon Sep 05, 2011 3:16 pm

No need to rewrite science. Just follow the dictionary;

How can noise be a "product" of "bandwidth"?

http://www.thefreedictionary.com/product explains clearly that "product" means something produced by human, mechanical effort or a natural process.

http://www.thefreedictionary.com/bandwidth states clearly "The numerical difference between the upper and lower frequencies of a band of electromagnetic radiation, especially an assigned range of radio frequencies."

Not with the best will in the world can I extract that a numerical difference can be seen as something that is producing a product.
It can allow it, but not produce. To produce noise you need an electromagnetic energy source. A numerical difference is an expression, not an source.

Furthermore: the part in the sentence after the comma in fact gives support to what I said in my previous post about the content of the article you referred to. "A range of radio frequencies". Thus not the amplitude of the radio wave.

I'm sorry, without re-writing science I can support my argument. How about you?
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Re: Calculate max wireless distance.

Mon Sep 05, 2011 5:59 pm

Honestly, 40 years in radio engineering and you are challenging me!!!!!!!!

http://www.qsl.net/va3iul/Noise/noise.html

The formula to find the RMS thermal noise voltage of a resistor is:
Vn = Root(4kTRB)
k = Boltzman constant (1.38*10-23 Joules/Kelvin)
T = Temperature in degrees Kelvin (K= +273 Celsius)
R = Resistance in ohms
B = Bandwidth in Hz in which the noise is observed (RMS voltage measured across the resistor is also function of the bandwidth in which the measurement is made).

http://sss-mag.com/ss.html
http://www.highfrequencyelectronics.com ... torial.pdf
http://cp.literature.agilent.com/litweb ... -8255E.pdf
 
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Re: Calculate max wireless distance.

Wed Sep 07, 2011 7:00 am

power is constant.

it is like having a litre of water pour it into a wide glass and the level of the water is low;
pour it into a narrow glass and the water level is high.

Get a simple book on audio amplifiers and get a grasp of power, it really is simple.

10db using a 5MHz channel is going be relatively more powerful than running 10db using a 20MHz channel.
It is that simple.

Power is like volume. (No pun intended).
 
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Re: Calculate max wireless distance.

Wed Sep 07, 2011 12:17 pm

power is constant.

it is like having a litre of water pour it into a wide glass and the level of the water is low;
pour it into a narrow glass and the water level is high.

Get a simple book on audio amplifiers and get a grasp of power, it really is simple.

10db using a 5MHz channel is going be relatively more powerful than running 10db using a 20MHz channel.
It is that simple.

Power is like volume. (No pun intended).
I think this conclusion was already established. What is your point?

If your point is that due the use of half the bandwidth (10Mhz instead of the standard 20Mhz) we get more power at the receiving end and due that the SNR increases and thus improves the link, we all already agree on that.

What I don't agree on is that the width of chosen channel (thus the amplitude of the wave) has any effect on the absolute noise level at the receiver. So, imho we are not bringing noise levels (noise floor) down by using 10 or 5Mhz channel.I find proof in my own system where I changed my whole network (16 AP's) from 20Mhz into 10Mhz in the last 6 months and noise floor levels didn't change noticeable anywhere. But SNR did due the slight increase in signal levels.
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Re: Calculate max wireless distance.

Wed Sep 07, 2011 2:46 pm

I have already detailed the equation above, what is wrong with you!!!

You see that in the equation for noise, it is square root of (bla times bla times bla times bla).. And one of the blas is "bandwidth"!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

http://www.sssoftware.com/docs/wnadoc/glossary.html (rudy, when I refer to "product" I am refering to product in mathematical terms, which you should have found in the english dictionary).

Thus bandwidth is in part of the equation that consists of products, ie they are multiplied together..

Now the full answer is that noise is square root of (blaxblaxblaxbla)... Thus if 40mhz bandwidth is 4 times 10 mhz bandwidth, then it follows that the difference will be the square root of 4 (2) or twice less than 40Mhz... OR 6dB.

(and before anyone jumps in, yes, 6dB not 3dB, because we are not talking about measurement of power, we are talking about measurements in uV (microvolts))

So in theory, a receiver passband of 10Mhz should have a 6dB higher dynamic range than a passband of 40Mhz.

TGrand, there is no such thing as 10db in power measurement!!!!!!!!!!

Rudy, you wrote
Bandwidth in the "receiving system" imho means the working range of a receiver circuit. Any signal outside this will theoretically not be allowed to be picked up and thus causes no ´noise´. By limiting the working ´bandwidth´ of the radio we only limit out of band noise. Not noise in the working radio band we use.

No this is absolutely incorrect, you are not understanding what noise is, you are thinking only of a bandwidth cluttered with signals.

The noise that we are refering to at on or around -104dbm is noise not weak signals. The noise is broadband (in audio we would consider it to be whitenoise) it may be noise generated by atmospherics, noise from the sun, or noise from components..

It is likely to be the later, noise from components!!. If you pass an AC current through a resistor then you will generate noise.. We are talking about ALL parts of the receiver circuit that "detect" "modify" or "amplify" the wanted signal.

Furthermore I encourage you to look at FFT, fast fourier transformation. Look at a spectrum analyser display when a signal is amplified in a linear fashion, then look at an RF signal that is "non-linear", look at the interference the "non-linear" (cheap radio cards that are over driven) causes to the spectrum. ( I think CB'ers would call it splatter).

An over-driven radio card or an amplifier driven outside of its design criteria into a region un-linear would produce rich harmonics all over the band, and this would certainly add to the noise.
 
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Re: Calculate max wireless distance.

Thu Sep 08, 2011 1:22 pm

I have connected the routers to my lab.

Here is a screen from the station router.

The antennas are stuck to each other. Are they seem ok?
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Re: Calculate max wireless distance.

Thu Sep 08, 2011 5:54 pm

No its not OK, the signal levels are way too high.

Why are you trying them out inside?

If I were you I would put them where they should be, select 5 mhz wide channel and try them out.

If it works ok with 5mhz bandwidth, then try 10Mhz... I wouldn't bother with 20mhz bandwidth as it looks like you have fresnel obstructions.
 
hlekat
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Calculate max wireless distance.

Thu Sep 08, 2011 7:01 pm

I was having a problem with the setup of the routers. Instead of making the troubleshoot in the mountain which is normally installed I choose to bring them to my lab for some testa.

I posted the results from the lab with the antennas in a very close distance in case you notice a problem.
 
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Re: Calculate max wireless distance.

Thu Sep 08, 2011 10:17 pm

Ok I understand..

The signals are way to high and as such the radio cards will behave abnormally at those levels.
So any figures/statistics are going to be meaningless.


If you have to test them on the same bench, can you use a "dummy load" resistor instead of antennas.
 
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Re: Calculate max wireless distance.

Thu Sep 08, 2011 10:48 pm

Ok I read backwards your posts..

1: Those antennas appear questionable .... The vswr you quote is not the same as I read in their specs.. when I read their specs there are stacks of errors on their specification pages... The real vswr is anything up to 1.7:1.

The polar patterns are incorrect for a panel antenna with this gain, the polar patterns shown are artificially drawn... I even suspect their spectrum analyser plot of gain, since the bandwidth resolution display is highly dubious.


I suggest, you fix one antenna to one of the sites and power it up.. I assume you have the latitude and longitude of both ends.. PM me with these and I will run it through Radiomobile program.

Drive 5km from the site under test, put other panel in car with RB and use a 12V-230V car invertor. Take measurement from site 5km distant with antenna in the clear and car parked behind antenna.

Drive 10km from site under test and take same measurements..

Report back to Forum.

If you believe that the fresnel zones are obstructed, then take these tests just before the obstruction and again just after, the results would then be conclusive.
 
hlekat
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Re: Calculate max wireless distance.

Fri Sep 09, 2011 12:10 am

I am not such as experienced user in the wireless networking. In fact this is my first attempt. :D and i will do it for personal use. I studied computers so I though a great idea to make it my own.

In my first attempt i haven't enabled the nvstreme protocol and i wasn't so familiar with the routers configuration. Know I have read some topics and I am better prepared. I will raise the mountain point 4meters and 2meters in the home.

To be honest I haven't understand that much the first part of the topic about the antenna specs because I am not familiar with antennas except their gain and their beamwidth. About the second part it is easier for me to raise the antennas.

The only problem I am seeing right know is that link calculator is giving a theoretical signal level : -66db
The same calculator says that links with signal levels <-70db are unstable.

So my first attempt was :
signal strength -92
noise floor : -105
snr : 13

I am not very optimistic about the tomorrow attempt.
I am very far away to go at least at -70db.

But we will find out tomorrow.
In case I am getting -80dB is it possible to have a stable link ?
 
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Re: Calculate max wireless distance.

Fri Sep 09, 2011 2:54 am

You would rather have -70s, but I do have several links in the -80s that are quite stable. It depends on your noise level and how clear the shot is.
 
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Re: Calculate max wireless distance.

Fri Sep 09, 2011 10:07 am

No, -80 is no good. I gather you dont need much throughput!. So I would be satisfied with -70.

(you need 10dB headroom, since links will fluctuate by 10dB, especially near the coast.)

your link looks very problematical since one end is on the coast, and the ther is on top of a hill inland. Almost the worse scenario. You will be constantly plagued by differing signal levels, since there will always be changes in moisture content in the air,

You not only have different altitudes, but coastal air and then inland mountain air! I can forsee many problems with temperature inversions and ducting.

I have one link that varies 30dB depending on temperature and moisture.
 
hlekat
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Re: Calculate max wireless distance.

Fri Sep 09, 2011 5:41 pm

Finally I raised both antennas.

1.5m at the home side and
2.5m at the mountan

I think that the results are good. One of the poe cables is having problem and i could not access the ap point, but it can power up the device. So I made the tests from the station side.

The routers were connected in the wlan status but i couldn't access the ap point from the station and i couldn't perform ping or bandwidth test to see the network performance. Although I couldn't connect etc the winbox from the station was showing both devices.

I will upload two pictures.
The signal rates and the output problem from the winbox when i tried to connect to the ap.
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