TX Power Settings Incorrect - Script by Consultant

RouterOS Wireless Networking
1

Hello Everyone,

I have a curly one that needs some advice. A few years ago I setup a small Wireless ISP. At the initial setup stage I hired a Certified Mikrotik Consultant to help with setup and design of our system. He kindly supplied a very useful .xls setup script to get us started and advise on how to setup OSPF, Power, Cards, links etc… I’ve been very impressed by his knowledge and assistance, we went through all the settings and configuration in detail for two days, I had further training with him.

It’s a few years on and I’m learning more, reading more and have been looking after the network comfortably for the last 3+ years. We now have 80+ hotspots and continue to grow. Mikrotik I Love your kit, your routeros isn’t bad either ;o)

Today I spent the second day on site in a location which we setup initially with the help of our consultant and the scripts he supplied. We have been troubleshooting a sudden drop in connectivity and quality of links. During the troubleshooting process I discovered that the tx-power settings were at 28. Recently I read that the best setting is default or default card rates. I didn’t really read more into it but was reviewing best settings and since seeing that have adjusted our script to “default”.

Today, I discovered that setting to 28 can cause burnout of cards. We replaced the R52 Cards and had the link set to default and things came back nicely.

This also helps us solve some other site issues as we’ve had a few sites over the last several months having strange performance issues, in-ability to connect, bad signal, bad CCQ. I’ve been racking my brains, looking for interference (also love wispy2) and other things that may of caused the issue. We’ve been installing new antennas in some sites. The sites still have issues and I will now be replacing the cards ASAP and seeing if it is instantly resolved (which I think it will be). We also played with the tx-power but generally left at the “advised” default setting of 28.

On my return from this site visit I’ve logged into all my radios and changed the tx-power to default. Now some radios were already set to default as they were after I had read about power settings and the recommendations for best setting. Some sites were set to 28 but current tx power displayed 19 or 17. Some were on 28 and current power was 28.

Why am I writing here? why not talk to the consultant to find out what the story is? Firstly he can be hard to get hold of, secondly, I would like community advice as I might be completely wrong about this being an issue.



My Questions.

Is setting power to 28 on cards, 65mW and 100mW going to cause them to burn out? (I think I now know that answer)
If Yes

  1. How do I test to see if cards that have been set to 28 are in fact damaged?
  2. What symptoms will best identify this?
  3. Why is a certified consultant giving me damaging and incorrect advice?
  4. I’m going to be losing, and have already lost alot of time=($/GRR), Who is responsible for this problem?
  5. Who is financially responsible for this problem?
  6. Should I replace all cards that have been incorrectly set, or wait until they fail?
  7. Other questions that you may think of that I can’t think of..?

I’m interested in your feedback on this, I’ve estimated the cost to replace all our R52’s at approx $12,000 including time, $7,500 for cards. That is all cards as I really couldn’t tell you for certain which ones have been over that limit and recycled, which ones have never hit above 25 (100mW), or 20 (65mW)

Thanks for your time, I know it’s a long one. Hope to see you all at a MUM soon.

2

Can’t really answer your questions directly, but here’s a rundown.

  1. In theory, radio cards should have firmware limits inside them which stops the software from increasing the maximum power beyond what is supported by the card’s hardware… that’s in theory

  2. In practice, I personally never try to overdrive a card unless it’s an extreme measure, and only then it’s just temporary (eg. to see if the cause of a bad link is simply lack of power or something else…)… very rare, I think I’ve only done it once or twice in my career.

  3. the manual-tx-power feature is there to REDUCE the tx power, not increase it. As in 1, radio cards are designed with a maximum power level. Going over that level will mean driving the electronics beyond spec.

  4. Finally, no matter whether your setup is good or bad, if it aint broke, don’t try to fix! In other words, it’s bad that you had a failed card and found out it was because of the overdriven card (if that’s at all possible), but if the other cards are working fine, I wouldn’t touch them… but prepare to have them changed over time.


    And one more thing… 20dBm = 100mW, 18dBm = 65mW

3

yes, if you increase the power over the default, it will work for a short time, and then the card will be damaged.

4
  1. Does every doctor diagnose and treat every condition correctly? Does every lawyer win every case? Does every mechanic fix every problem in every car? Is every building that every architect builds safe? Being certified/educated/licensed doesn’t mean someone always does everything right.
    4 & 5. You could have checked the forum and manual for a second opinion and realized that the consensus is that overdriving a radio card is a big NO NO. Blame yourself for listening or blame the consultant for giving incorrect information, but it is most certainly not MikroTik’s fault.
  2. This is a business decision. Compare the cost of downtime vs. the cost of replacing cards which are still OK.

As andreacoppini wrote, the manual TX settings are ALWAYS for reducing, not increasing, TX power.

5

Thanks very much for your comments. I appreciate them.

  1. Does every doctor diagnose and treat every condition correctly? Does every lawyer win every case? Does every mechanic fix every problem in every car? Is every building that every architect builds safe? Being certified/educated/licensed doesn’t mean someone always does everything right

It’s just I recall talking about tx-power and 28 being an “ok” setting. However, It’s a lesson for me, I should of read a bit more perhaps and now I know. Don’t believe everything. My bad :slight_smile:.


  1. Finally, no matter whether your setup is good or bad, if it aint broke, don’t try to fix! In other words, it’s bad that you had a failed card and found out it was because of the overdriven card (if that’s at all possible), but if the other cards are working fine, I wouldn’t touch them… but prepare to have them changed over time.

Everything seems to of settled, connections are ok at default even after some time being over powered.


Any one have any methods of testing potentially faulty cards?

Thanks all for your advice.

6

You’d need a spectrum analyser, and someone who knows what he’s/she’s looking at…

A simpler way would be to compare it with a known good card (eg. a brand new one). Set it all up on a bench and run a bandwidth test through the good card for a while, then take TX Signal Strength readings. Swap out the card with the suspicious one, and do the same, compare notes.

Just make sure that:

  1. Everything else stays the same, right down to which slot on the routerboard you use and frequency.
  2. Don’t put the receiving card very close, as this will overdrive the receiving end and give you false results.
7

We use a Praxsym t-meter to test them. It is easy to use and portable so I can take it up the tower if needed.

But they are not cheap so it only makes sense in a larger network where you can justify the cost.

http://www.roc-noc.com/home.php?cat=13

Tom

8

Great Guys Thanks!

I’ve just hired a RF engineer, he has a Bird Meter, we’re looking for the 2.4Ghz Slug. He’s got a bunch of tools, although he comes from an FM background so some of them don’t instantly transfer across to us, but he knows his stuff so I’m happy to hand all this over to him and continue on my journey of discovery in other areas.

Cheers

9

Hi to all, sorry if I resume an old discussion…

In many sites there were 433MHz and 2,4GHz, so sometimes I completely made new installation, other times I had to use old cables.
In this way I calculate attenuation of cables and connectors and I correct “antenna gain” value in RouterOS.
As result, with low gain antennas, if I set “default” in tx power settings (using regulatory domain in CM9 or R52 cards), I got wireless card working at maximum power for lower rates (1 or 6 MB).

Now I got several radios not working good: using snooper I see a lot of free channels, and received signal is about 10dB lower than installation values.
I changed radio and I put Metal 5 for test: I receive correct expected signal power and I see much more AP using snooper.

So my doubt is:

  1. if I use wireless cards at maximum power (in “default” mode), will I damage them?
  2. if “default” maximum power is (x example) 17 dB at minimum rate, how much should I decrease power to work in “safe” mode? 2-3 dB is enough?

Thanks.

10

No, “default” mode can’t damage them. The above discussion is not valid anymore, it is near impossible to damage a radio just by misconfiguring RouterOS.

I suggest to leave always Default, unless you want to lower the signal radius.

That device could have been damaged in some other way, ESD discharge during thunderstorms is a common cause. You should use grounding and ESD protection to avoid this in future.

11

You’re absolutely right, but they can easily be damaged if they are powered up without an antenna attached. This applies to all transmitters, always have an antenna attached


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