Signal strength fluctuating with NV2: 900 Mhz, 20 Mhz. channel width

RouterOS Wireless Networking
1

On some of our 900 MHz. point-to multipoint links, the signal strength and SNR intermittently become poor when using NV2. We’re using Ubiquiti XR9 radios. The problem usually lasts a minute or so, then goes away for a few minutes, then returns for a minute or so. If we use 802.11 on these same links, we don’t have the problem. It usually happens when we use a NV2 on 900 Mhz. with a 20 MHz. channel width. Not all of our 900 Mhz. links with 20 Mhz. channels experience this. If we use a 10 Mhz. channel width, we don’t have the problem. Anyone else experienced this or have any suggestions?

2

Sounds like interference

3

If you experience an interference issue with nv2 every few minutes, then I suspect you would be experiencing interference issues with 802.11 also.

Things I would consider:

  • Run a frequency usage for several minutes
  • Are there other APs near-by ( any band ).
  • On every device, interface - Reset mac address
  • On every device, bridge - disable stp & disable rstp
  • Do all devices have the correct nv2 key ?
  • Do you use wireless access-lists ?
  • Try setting hw retry counts to 15 on everything
  • When the problem happens in nv2 mode, what do the logs show pre and post problems ?
4

If you experience an interference issue with nv2 every few minutes, then I suspect you would be experiencing interference issues with 802.11 also.

Things I would consider:

  • Run a frequency usage for several minutes
  • Are there other APs near-by ( any band ).
  • On every device, interface - Reset mac address
  • On every device, bridge - disable stp & disable rstp
  • Do all devices have the correct nv2 key ?
  • Do you use wireless access-lists ?
  • Try setting hw retry counts to 15 on everything
  • When the problem happens in nv2 mode, what do the logs show pre and post problems ?

I tried all of these suggestions, and none of them made a difference. It seems to have the problem whether I’m using NV2 or 802.11, 10 MHz. or 20 Mhz. I checked the logs on the client end, and there are frequent entries that say “no network satisfies connect list. By default choose with strongest signal.” The only answer that I can come up with it that it’s interference.

5

Hy,

have you tried a spectrum analyzer ($$$) ? MikroTik’s built-in tools are good, but no replacement to the analyzer.

Maybe there’s something around that’s using non-Wi-Fi 900MHz and you won’t see it with the basic MT tools. Old wireless phones and baby monitors are good examples of that.

Ciao,

AC

6

  • One time, I set up a 900 MHz system. It had all kinds of problems which I tracked down to be a near-by upper 800 MHz pager system running at several thousand watts.

  • Another time, I set up a 900 MHz system. It had all kinds of problems because of near-by high-power FM radio station transmitters.

  • Another time, I set up a 900 MHz system. It had all kinds of problems because of a near-by million+ watt multi-band military/FAA rotating radar system.

  • Another time, testing out a 900 MHz Motorola Canopy system, I had simular and frequent link drops. Motorolla suggested installing some $400 tuned band-pass notch-filters on each 900 MHz Motorola device. I shelfed the 900 MHz Canopy system because I was not going to pay an additional $400 bucks per device to bring up a 900 MHz system.

Although the above problems were caused by other devices not in the 900 MHz band, I suspect the 900 MHz cards I was using had poor near-by frequency band filters (or no adjacent RF band filters) which resulted in noise getting into my 900 MHz cards.

When it comes to the 900 MHz band, I suggest and only use 900 MHz links on near-by close links where my signal strength between Mikrotiks is hot and preferably stronger than -60 db and where you get good CCQ results. Thus - I over-design & overbuild my 900 MHz systems for better than normal signal-to-noise enviornments.