I have a couple of RB751U-2HnDs that work ok but I haven't been greatly impressed with the wireless performance on this model. I ran a spectrum scan on these and see a huge amount of noise just above the 2.4 band that can peak out up at about -20 db. This noise has the be generated by the radio card itself and I am wondering whether this is what is impacting my wireless performance. It's not on the frequency I am trying to use but is populating the 80 MHz just on the upper side of the US 2.4 band.

Any one have any information on this and is there a way to get rid of it?

it is definitely not generated by the device. it's possible that something else generates it.

I thought that too at first however I have two different 751s in two far different locations and both are showing the exact same noise. Any ideas on that?

How are you measuring it? Maybe they both are subjected to this noise, but our designers are certain that it can't be the one generating it.

I'm looking at the large red block shown on this spectral scan from within the mikrotik. Please see the attached screenshot.

Any update on this mikrotik support? Why am I seeing such noise on the spectral scan on multiple units and in multiple locations?

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I'm also seeing it...

RGDS
Jörgen

The problem I have is that this noise creeps into the US 2.4 band right at 2472 which is the upper side of channel 11 on 20 MHz. This is a problem on using channel 11 since there is no guard band between the noise and my channel 11 data. Since this unit is designed to be a SOHO router, you can't change many factors from the default settings and still get laptops and other devices to connect.

Posting mine for comparison purposes, device RB751G-2HnD, regards.

The 2GHz band is very crowded in all areas of the world. Would it be possible that this is simply interference from nearby 2GHz devices?

Interference doesn't usually show up the exact same in every location. I find that solution a little hard to believe since moving the device doesn't show a difference in the readings at all. The noise has to be coming from inside the device. It may not be the radio card but I think it's something inside the device.

Where are you both located? Is the unit indoors? We have tested this extensively, the board does not emit anything. It has also passed CE and FCC, which would be not possible if it would radiate something.

It is possible, that this frequency is used by some commercial equipment. For example in our country, some ISPs use this stuff: http://en.wikipedia.org/wiki/Multichann ... on_Service

Try to put the device in some aluminum foil and put it inside some seriously thick metal box. You will see that this interference will disappear.

I will try those tests and get back with the results.

It could be some analog link too. I have seen analog wireless security cameras using 2.4 GHz in some sites. This blocks all wlan communication in channels affected.

Attachment shows analog security camera in about ch1 blocking about half of 2.4 GHz wlan channels. Then it was turned off.

Bluetooth also. And of course microwave ovens.

Microwave ovens operate at 2450 MHz. I doubt if they could leak radio power so You could see it on the wifi scanner.

Bluetooth and microwaves both work in the 2.4 band but as Raf noted microwaves operate around 2450. Bluetooth also uses very small chunks of the regular 2.4 band and not the huge piece that is being seen on my scan above the 2.4 band.

I'll try and get that test done as soon as I can but things have been busy.

If you mean microwave oven, it has to be turned on to cause interference, no? There's no restaurant in our neighbourhood which would use microwaves 24/7. And I don't use mine more than once a day for 1min. I'll turn off the cable modem which is next to the router to see if it makes a difference though.

So I did the test you requested and found unfortunately that the noise got over 10 db higher. This actually proves the noise is coming from inside the 751 somewhere and I have 2 different units doing it.

I am getting the same results with RB751U-2HnD, RB751G-2HnD and RB711UA-2HnD with swivel antennas ... all three devices are very far away (100km+) so it is impossible for them to share the same signal source .... unless there is a satelite gone bezerk somwhere above central europe. Routeros 5.19 on all three, dude 3.6.

I guess my suggestion to anyone wanting to try one of these units would be to just go with something else since we can't seem to get rid of this crazy noise inside these boxes.

I guess my suggestion to anyone wanting to try one of these units would be to just go with something else since we can't seem to get rid of this crazy noise inside these boxes.

Has anyone tested the new RB2011UAS-2HnD for this issue?

It is most likely that your unit is transmitting at the time, so your foil reflects it back onto it. We are making a test right now, to see if it's true. Like I said, change the frequency on the unit, to see that the spectral scan image will change too.

I have changed the frequency on the unit and actually at the time of the testing, there were no wireless clients connected to the unit.

I guess my suggestion to anyone wanting to try one of these units would be to just go with something else since we can't seem to get rid of this crazy noise inside these boxes.

Has anyone tested the new RB2011UAS-2HnD for this issue?

Yep just did, none at all, and on my RB751G-2HnD i do not have the noise.

Sounds to me like there might be just a bad run of hardware maybe on the 751's?!

Sounds to me like there might be just a bad run of hardware maybe on the 751's?!

Maybe indeed, i got 2 RB751G-2HnD's here and both dont have it, so i guess its maybe a bad batch.

We also noticed the noise when we were mounting some 751U boards to a marina. We thought we are catching some radar freq., but we had the same problem when we tested same boards (as well as some other from the different batch) inside our company where other Mikrotik equipment didn't see anything similar...

Sounds like there is a problem with some of the later 751U hardware since we have a few people all seeing the exact same thing. Unfortunately, that just means to me that I will not be using this Mikrotik device and will thoroughly test the wireless of any future hardware before putting it into production.

Sounds like there is a problem with some of the later 751U hardware since we have a few people all seeing the exact same thing. Unfortunately, that just means to me that I will not be using this Mikrotik device and will thoroughly test the wireless of any future hardware before putting it into production.

Don't get me wrong. The device is working perfectly, it is just that piece of specter that is confusing. We deployed tons of them and we haven't had a single problem. They are doing a great job regardless of that strange signal.

Sounds like there is a problem with some of the later 751U hardware since we have a few people all seeing the exact same thing. Unfortunately, that just means to me that I will not be using this Mikrotik device and will thoroughly test the wireless of any future hardware before putting it into production.

Don't get me wrong. The device is working perfectly, it is just that piece of specter that is confusing. We deployed tons of them and we haven't had a single problem. They are doing a great job regardless of that strange signal.

Could you please share your positive/negative experience about 751U device? What is your use case?

Sounds like there is a problem with some of the later 751U hardware since we have a few people all seeing the exact same thing. Unfortunately, that just means to me that I will not be using this Mikrotik device and will thoroughly test the wireless of any future hardware before putting it into production.

Anyone else besides me seeing this issue on 711UA-2HnD ?

BTW, just noticed that if I decrease sample time in spectral scan from default 10ms to 1ms problem is much less visible on 711.

My unit works ok but I have trouble getting completely fast and reliable performance out of the wireless interface especially using channel 11 up right next to the noise I'm seeing. I can get better performance from a Ubiquiti AirRouter on it's wireless. I bought these unit because I couldn't get my hands on a 951 but I think I'm just going to try a 951 next.

My unit works ok but I have trouble getting completely fast and reliable performance out of the wireless interface especially using channel 11 up right next to the noise I'm seeing. I can get better performance from a Ubiquiti AirRouter on it's wireless. I bought these unit because I couldn't get my hands on a 951 but I think I'm just going to try a 951 next.

Anyone knows what is the official position from Mikrotik on this issue? ... is it a bad batch, design error, software error or what? Is it software fixable, waranty issue or will there be a recall on these units? The noise effects functionality on ch11 and higher.

JF

We are looking into it, and it currently looks like v5.21 will fix the issue.

Has anyone done a scan with another spectrum scanning device placed in with the RB751 to confirm that it actually is sending out that interference?

Be interested to know if it shows up on something like a wispy and is actually the 751 kicking out interference or if it's simply some kind of data processing error that is causing "The Dude" to think it's seeing interference.

Seems to me like calibration issue