Hello,

Today some of my clients complain about limited connectivity when i visit and i saw signals are too much low. From the start the signal in that area was 21DB and now its only 10DB. Signal also gone low in different areas.

i am using Wireless (Atheros AR5213) wireless cards.

Settings is not changed. I also restore a backup of settings but problem is still there.

card settings is the following
One last thing TX power id 30dbm.

Signal strength is given in dBm and should be somewhere between -90 and -25. (Notice the negative!)
Smaller is stronger, but stronger than (or "lower than") -30, or preferably -40 is not recommended. Most radio's become unreliable when hit by too strong signals.

By using dB you are probably referring to the Signal To Noise number. This number tells you how good the reciever hears the signal from an antenna compared to the surrounding noise levels it picks up.
15 to 20dB is already marginal. If atmospheric or spectrum conditions change it will even become worse with the effect the links becomes unstable and unreliable. I take 30dB as the bottom in general for all my links.

To increase the Signal To Noise you have several options:
- Use higher gain antenna for better listening.
- Use quality antenna and shielded radio for lower noise levels at the receiver circuits.
- Use directional antenna from client towards AP. It reduces noise and increases signal fm AP compared to omni.
- Use higher gain antenna on AP
- Use higher power radio on AP
- Give better LOS for the links (higher poles for antenna mounting)
- Change frequency.

I can think of even more issues so to really give you good advices we need more info.

21DB and now its only 10DB

this doesn't seem correct.
this is how you read signals:

-30dB too strong signal, bad
-50dB excellent good signal
-60dB good signal
-70dB bad signal
-80dB terrible signal, probably will disconnect often

If all was well and signal strength suddenly drops you may want to take a closer look at your card. Like Rudy said, there's a long list of possible causes and we need more info.
What type of card are you using (brand and model)?
What does output of look like? I'm interested in the noise floor, tx-ccq and if there are any errors.

21DB and now its only 10DB

this doesn't seem correct.
this is how you read signals:

-30dB too strong signal, bad
-50dB excellent good signal
-60dB good signal
-70dB bad signal
-80dB terrible signal, probably will disconnect often

Normis, please can you keep the standard and not add more confusion?

Decibel (dB) and dB relative to a milliwatt (dBm) represent two different but related concepts.
Given the numbers and the "dB" rajamani779 is obviously looking at the s/n levels.

Normis, your example should read:
-30dBm too strong signal, bad
-50dBm excellent good signal
-60dBm good signal
-70dBm bad signal
-80dBm terrible signal, probably will disconnect often.

Use dB when expressing the ratio between two power values. Use dBm when expressing an absolute value of power.
(http://www.isa.org/Content/ContentGroup ... s__dBm.htm)

You don't have to specify m (relative to mw) if everyone knows what is being talked about. Are you telling me that RouterOS also shows some other dB somewhere?

If rajamani779 is referring to signal strengths when writing:

i saw signals are too much low. From the start the signal in that area was 21DB and now its only 10DB.

than it would mean his antenna's are almost physically attached to each other to get 10DB(!) signal!
Since he also uses "DB" and looking at the numbers and the fact there is no "-" in front of these numbers and the fact the number in itself degreases, not increases, I could bet he is looking at the S/N level.

Imho it is obviously he is mistakenly reading the S/N levels for signal.

You don't have to specify m (relative to mw) if everyone knows what is being talked about.

ROS uses dBm for signal levels, not dB. So why should you now start omitting this "m" when referring to signal levels? I doubt seriously that everybody on this forum really knows what he is talking about. If that would be the case the forum would loose half of its users....

For most readers this is only adding to the confusing. Stating that most readers would understand what you mend to write is expecting too much imho. I even raised my eyebrow when I saw your comment. Or am I now the one being the ´dummy´ here?
Your last sentence is not even understood to its full merits by me. Where do you conclude I see ROS using ´some other db(?) somewhere´.

read wikipedia on what dB means.

21DB and now its only 10DB

this doesn't seem correct.
this is how you read signals:

-30dB too strong signal, bad
-50dB excellent good signal
-60dB good signal
-70dB bad signal
-80dB terrible signal, probably will disconnect often

Normis i am using TPlink 500g with 12dbi Antenna. I saw that signals in the AP. On server its -71dBM.

If all was well and signal strength suddenly drops you may want to take a closer look at your card. Like Rudy said, there's a long list of possible causes and we need more info.
What type of card are you using (brand and model)?
What does output of

Code: Select all

/interface wireless monitor 0

look like? I'm interested in the noise floor, tx-ccq and if there are any errors.

Result is follow

status: running-ap
band: 2.4ghz-b
frequency: 2462MHz
noise-floor: -99dBm
overall-tx-ccq: 97%
registered-clients: 1
authenticated-clients: 1
current-ack-timeout: 30
nstreme: no
current-tx-powers: 1Mbps:30(30),2Mbps:30(30),5.5Mbps:30(30),11Mbps:30(30)
notify-external-fdb: yes

read wikipedia on what dB means.

its DBM in above post i wrote wrong. Its DBM not db. i check again on AP and server.

Answer of WirelessRudy reply.

To increase the Signal To Noise you have several options:
- Use higher gain antenna for better listening.
i am already using Sector and TPLINK grid 24dbi. My client i mentioned above signals and other is 600 Meter away from base.

- Use quality antenna and shielded radio for lower noise levels at the receiver circuits.
Antennas are company made and its good. Noise floor is mentioned in above post.

- Use directional antenna from client towards AP. It reduces noise and increases signal fm AP compared to omni.
Client is to much near but i am also using 12dbi Directional antenna on client end.

- Use higher gain antenna on AP
all antennas are high gained. they are providing great signal but suddenly they drops signal.

- Use higher power radio on AP
answered above.

- Give better LOS for the links (higher poles for antenna mounting)
Antennas are 70 feet higher from earth.

- Change frequency.
i also do and check. but they start overlapping now i am using 1,6 and 11 frequency. As standard.

rajaman you are looking in the wrong place. that number is not the signal level.

look in this menu:

/interface wireless registration

rajaman you are looking in the wrong place. that number is not the signal level.

look in this menu:

/interface wireless registration

Yep! i am looking signal strength of user in this menu.

i think some miss understanding creates there. i want to clear you.

A client with name A have signal -68 on server and 21dbi on AP. But suddenly signals goes down and now he is getting only -71 or -72 Dbm as shown in server and 10db on AP. i also reset and update firmware of AP but still same problem.

Ok, what i can distill so far is the following:

You take readings from the AP, probably the TP link doesn't have a link status? (Or if it has, what are the readings there?)

You use 2,4Ghz channel, ´b´ mode only.
Your signal from one of the clients is -71dBm (? correct me if I am wrong.) This is the signal AP receives from the client? (Not the other way round? The register gives both, Tx and Rx signal. Read the Rx here.) The given S/N for that clients relates to that signal since the noise level shown is also only known at the unit we read the settings, the AP. (For noise level at the client we should look at the info in the client unit.)

The S/N reading for that client was 20dB and suddenly fell to 10dB, yeah?
Given a noise-floor level at the AP of -99dBm this means that the signal received from the client fell from -79dBm (-99 + 20s/n = -79) to -89dBm ((-99 + 10s/n=-89).I would say that -79dBm signal is marginal but workable, but -89dBm is really poor to bad.

Reason for the drop:
- Send chain on clients end. (radio card, connector, cable, antenna.). Since you said more clients suffered from the same issue this reason is not very plausible though. So lets start looking at the AP first.

- Receive chain on AP:
- Radio card can be bad. Too hot? Problem only during the day when temperature is high?
- Good fit cable and antenna? No water ingress in the connectors?
- ESD? Make sure both board, radio and antenna are connected to good and same ground. Small esd's do have effect on receive sensitivity of cards.

Other reason can be interference from other 2,4Ghz working devices. (Not necessarily Wifi! Think of baby-phone, wireless security system, camera's, microwave etc. etc. Scanner in ROS won't ´see´ these but they still can have influence!)
In this case the noise level of the AP could drop. Is the -99dBm you showed us stable? Or does it fluctuate a lot?

You are also using 802.11b only. Now it can even be that a 802.11b/g (or even ´n´) foreign unit is using same or adjacent channel. Your AP won't see it but still get interference from it!

My suggestion is to do a wireless scan in ROS on the AP in both b/g band enabled and both 10 and 20Mhz bandwidth. (So two scans.)
This way at least you will learn if any concurrent AP's are giving problems...

Let us know how you're going....

read wikipedia on what dB means.

Extracted following from Cisco website (very interesting for learning all about wireless link parameters):

- http://www.cisco.com/en/US/tech/tk722/t ... 2d37.shtml
In this document they use "dBm" for power as well for SNT (or S/N, Signal-to-Noise Ratio).
"dB" is used for ´Fade Margin´ and for ´Free Space Path Loss´

- https://supportforums.cisco.com/docs/DOC-12954
In this forum they use "dB" for both power as cable losses and antenna gain!

- https://supportforums.cisco.com/message/1279955#1279955
Imho best answer is given in this topic by ´blue.modal´
(Interesting to read about the dBi versus dB reading for antenna's)

Even Cisco is creating a bit of confusion for the innocent reader!


After reading the info in wikipedia it teaches that basically "dB" is used for showing the ratio between one signal towards an other. I.e. the difference between the signal strenght of the antenna we want to ´hear´ and all the rest of the signal we don't have interest in. (But still ´hear´, simply because they are there....)
In the purpose of this topic; signal of antenna towards background noise, or Signal to Noise, measured in "dB"


Other info extracted from wikipedia:

"dBm" is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form.
In the purpose of this topic; signal level that is received by radio from remote radio.

"dBi" dB(isotropic) – the forward gain of an antenna compared with the hypothetical isotropic antenna, which uniformly distributes energy in all directions.


So, I have to give some credit to normis (No, no karma, you are not part of that game! ) Wikipedia teaches us dB can indeed be used for all purposes as long as user has thorough understanding of the terminology and its meaning.

But to make things more understandable and easier to work and compare extra add-ons to the "dB" term have evolved and are established. Like dBm and dBi.
I think if we just stick to what ROS is mentioning in its readings, "dB" for S/N and "dBm" for (field)power, we all know what we are talking about. ROS reading notifications are widely accepted and give best understanding when discussing wireless links and how they work.

Back to the original issue?

Ok, what i can distill so far is the following:

You take readings from the AP, probably the TP link doesn't have a link status? (Or if it has, what are the readings there?)

You use 2,4Ghz channel, ´b´ mode only.
Your signal from one of the clients is -71dBm (? correct me if I am wrong.) This is the signal AP receives from the client? (Not the other way round? The register gives both, Tx and Rx signal. Read the Rx here.) The given S/N for that clients relates to that signal since the noise level shown is also only known at the unit we read the settings, the AP. (For noise level at the client we should look at the info in the client unit.)

The S/N reading for that client was 20dB and suddenly fell to 10dB, yeah?
Given a noise-floor level at the AP of -99dBm this means that the signal received from the client fell from -79dBm (-99 + 20s/n = -79) to -89dBm ((-99 + 10s/n=-89).I would say that -79dBm signal is marginal but workable, but -89dBm is really poor to bad.

Reason for the drop:
- Send chain on clients end. (radio card, connector, cable, antenna.). Since you said more clients suffered from the same issue this reason is not very plausible though. So lets start looking at the AP first.

- Receive chain on AP:
- Radio card can be bad. Too hot? Problem only during the day when temperature is high?
- Good fit cable and antenna? No water ingress in the connectors?
- ESD? Make sure both board, radio and antenna are connected to good and same ground. Small esd's do have effect on receive sensitivity of cards.

Other reason can be interference from other 2,4Ghz working devices. (Not necessarily Wifi! Think of baby-phone, wireless security system, camera's, microwave etc. etc. Scanner in ROS won't ´see´ these but they still can have influence!)
In this case the noise level of the AP could drop. Is the -99dBm you showed us stable? Or does it fluctuate a lot?

You are also using 802.11b only. Now it can even be that a 802.11b/g (or even ´n´) foreign unit is using same or adjacent channel. Your AP won't see it but still get interference from it!

My suggestion is to do a wireless scan in ROS on the AP in both b/g band enabled and both 10 and 20Mhz bandwidth. (So two scans.)
This way at least you will learn if any concurrent AP's are giving problems...

Let us know how you're going....

Thanks Wireless Rudy for prompt replies. Cables are good and tight no water in that. On 8.2.11b we got 27 signal strength on AP of tplink. So 802.11b/g is not issue.

One more thing i want to tell you. My Tower don't have earth cable.. After bad weather and lightning this issue occur. So what you said about it. i think its WIRELESS CARD PROBLEM. they are not given full TX power. what you said. is this problem in Card?
i also have tplink 5210 CP that device signal is also gone low after the bad weather.

Thanks Wireless Rudy for prompt replies. Cables are good and tight no water in that. On 8.2.11b we got 27 signal strength on AP of tplink. So 802.11b/g is not issue.

One more thing i want to tell you. My Tower don't have earth cable.. After bad weather and lightning this issue occur. So what you said about it. i think its WIRELESS CARD PROBLEM. they are not given full TX power. what you said. is this problem in Card?
i also have tplink 5210 CP that device signal is also gone low after the bad weather.

Well, the bad weather with lightning is a good finger pointer....

Even if your tower suffered no direct hit, the high electro static energy in the air during such storms could have damaged your radio's in the tower. Just fit a new card and see if your problems are over. If they are start thinking of some good grounding and eventually lightning protection.

I am still a bit confused in what you write. Your AP is a Mikrotik unit, yes? So the TPlink's are client units connecting to that AP?
Signal reading "27"; if this is the real signal reading (so not S/N) than this is way too high! Can you show me a screendump of the AP's wireless registration table? Or the wireless client properties in that table?
Your numbers are so strange I still have the ´feeling´ you read something different than what you think you are...

Thanks Wireless Rudy for prompt replies. Cables are good and tight no water in that. On 8.2.11b we got 27 signal strength on AP of tplink. So 802.11b/g is not issue.

One more thing i want to tell you. My Tower don't have earth cable.. After bad weather and lightning this issue occur. So what you said about it. i think its WIRELESS CARD PROBLEM. they are not given full TX power. what you said. is this problem in Card?
i also have tplink 5210 CP that device signal is also gone low after the bad weather.

Well, the bad weather with lightning is a good finger pointer....

Even if your tower suffered no direct hit, the high electro static energy in the air during such storms could have damaged your radio's in the tower. Just fit a new card and see if your problems are over. If they are start thinking of some good grounding and eventually lightning protection.

I am still a bit confused in what you write. Your AP is a Mikrotik unit, yes? So the TPlink's are client units connecting to that AP?
Signal reading "27"; if this is the real signal reading (so not S/N) than this is way too high! Can you show me a screendump of the AP's wireless registration table? Or the wireless client properties in that table?
Your numbers are so strange I still have the ´feeling´ you read something different than what you think you are...

Yes i am doing grounding. i think i have some interference in signals. Sometimes signal come's up and down. I have 4 AP's. 2 sector east and west.
1 grid in south and 1 tplink 5210 access point in north.

1 Sector on East on Channel 1, And West Sector is on Channel 11.

Grid on Channel 6 and Tplink 5210 on Channel 13.

My client i discuss above is on Sector 1 (East). is channel settings is right?

I am still a bit confused in what you write. Your AP is a Mikrotik unit, yes? So the TPlink's are client units connecting to that AP?
Signal reading "27"; if this is the real signal reading (so not S/N) than this is way too high! Can you show me a screendump of the AP's wireless registration table? Or the wireless client properties in that table?
Your numbers are so strange I still have the ´feeling´ you read something different than what you think you are...

On Many point i have 27 and 30 signal strength on TP 500g AP. But on server it shown -70 or -67. I attach server registration table. On these two clients i have 28 and 30 db on AP.
Two AP with ending MAC 34 and 5B have 27 and 30 signal strength.

AP in Blue box with ending B7 is issue. On device he is receiving only 10 and i also change device but same problem. I also check on different place in opposite direction. But problem is same also on new point.

One more thing i want to tell you. My Tower don't have earth cable.. After bad weather and lightning this issue occur. So what you said about it. i think its WIRELESS CARD PROBLEM. they are not given full TX power. what you said. is this problem in Card?
i also have tplink 5210 CP that device signal is also gone low after the bad weather.

Yes i am doing grounding.

This is obviously contradicting. First you say you have not grounded the tower and now you say you do???

i think i have some interference in signals. Sometimes signal come's up and down.

That could be a sign or interference yes.

I have 4 AP's. 2 sector east and west.
1 grid in south and 1 tplink 5210 access point in north.
1 Sector on East on Channel 1, And West Sector is on Channel 11.
Grid on Channel 6 and Tplink 5210 on Channel 13.

OK, so you probably have routerboard with 3 cards for your east, west and south antenna's and one separate unit (TPLink) for the north.
3 radio's in one board and box is not recommended. They tend to interfere with each other.
But worse is the TPlink. It is on channel 13 while you have already a radio on channel 11 in the same tower. This is asking for problems. Channel 11 and 13 are partly overlapping each other and since both radio's probably are close together they interfere with each other.
If radio with ch11 is facing west and radio with ch13 is facing north they could even create interference on a
radio facing South or East.
So my next question is: How far are these antenna's physically separated from each other and what is their back to front ratio. (How much signal is radiated to the back compared to the front.)
Also, you don't mention the kind of antenna of the TPLink. Is this an omni or sector or directional?

Further more, in 2,4Ghz you basically only have 3 separated channels. 1, 6/7 and 11/12/13.
If you now want to setup a tower with 4 sectors you can do the following:
Use two mimo able radio cards (802.11a/b/g/n, they come with two antenna connectors)
Connect to each of the connectors a sector. You can use side by side or opposite. (What is best is not decided yet. This is a very new way of using card, some forum user ´ramos´ came up with the idea.)
Now, set the card to work in normal 802.11b/g mode and each card will transmit and receive through both antenna's (chains).
It works, I do it myself on two units in 5Ghz to save frequencies and it works to full satisfaction!
This way you only have to use two different frequencies and only two cards that fit in one board!
Save money and stay out of problems! As a bonus, since only one routerboard is needed you probably even get a slightly better performance of you network! And you can maintain one registration table for all your clients!
How many more presents do you want!

On Many point i have 27 and 30 signal strength on TP 500g AP.

This kind of reading I still don't understand. Can you show me a screen print?

Two AP with ending MAC 34 and 5B have 27 and 30 signal strength.

I don't see that..

AP in Blue box with ending B7 is issue. On device he is receiving only 10 and i also change device but same problem. I also check on different place in opposite direction. But problem is same also on new point.

Please explain! This makes no sense to me.
Anyway, make a new print but include the column for S/N and CCQ in the table. Your problem link shows marginal signal with very low connector rate. You probably find the CCQ very low and the S/N also marginal. I think this link suffers most from interferences.

You should have started this topic with the fact that you are not using MikroTik gear for your AP. Anything could be the cause now, I can't help you if the AP is not MikroTik.