XR9 waveform power output and co-location of radios

RouterOS Wireless Networking
1

This goes along with the testing I posted earlier today, but instead from the point of view of co-locating multiple radios near each other and how significant adjacent channel interference will be. You can find the earlier info here: http://forum.mikrotik.com/t/sr9-and-motorola/16457/1

I took readings of power outputs on all 4 channels, after documenting all possible frequency/channel width combinations I arranged them by frequency, and by channel, to easily compare received power levels on each channel width and frequency selection, as well as actual frequency utilization. The charts are below, so you can review them and come to your own conclusions, but here are mine.

output power levels are most even across channels 907 and 912 in any channel width, while 917 seems to output the power on average, it seems to go from roughly 5db weaker at the bottom of the channel, to a 5db stronger at the top half of the channel in all channel widths leaving a (roughly) 10db difference in power output across the width of the channel, and at least on my test radio, 922 seems to have power output problems at any channel width, it is probably best to avoid this channel in any mode (I will try to test with another radio at a later date to confirm if this is isolated to the radio, or common across the product line)

Channels you can safely co-locate / operate near each other:

Using 5 MHz channels: any non-adjacent channel can safely exist in the same area, adjacent channels will receive interference roughly -20db weaker then the received signal strength, recommend different antenna polarities if using two adjacent 5 MHz channels in the same area.

Using 10 MHz channels: any non-adjacent channel can safely exist in the same area with minimal effect from other channel, recommend different antenna polarities if using two non-adjacent 10 MHz channels in the same area. Adjacent channels will cause significant interference and should not be used near each other.

Using 20 MHz channels: no combination can co-exist in nearby areas without causing significant interference

20 MHz channel modes are not supported at 907 MHz, yet it appears to function, but below the ISM band lower boundary. At 922 MHz 20 MHz channels do not function at all (this is not un-expected as it is an unsupported frequency. channel width combination).
XR9 Channels.jpg

2

That is some really good information. It also sheds some light on why most of my radios seem to work best at 907mhz. I was running in B mode on 907 (which I know isn’t supported) but it seemed to work really well and B mode dealt with interference better.

Also, I have an SR9 and XR9 both colocated about 5 feet from each other both cards in the same RB532. The SR9 is hooked to a 9dbi yagi, and the XR9 to a 12dbi 120 degree sector, both in horizontal polarization. I have the SR9 set at 2437 and the XR9 at 2427, which according to the charts I’ve seen correspond to 907 MHz for both cards. Can anyone confirm that?

I actually spent more time finding the channels that reported the lowest noise and performed the best, and afterwards realized I was running both radios on what I believe to be the same frequency, which I had always assumed wouldn’t work well at all, but it is the combination that works best…

So… is your conclusion that you shouldn’t run on the same or overlapping frequencies, or that it shouldn’t even be possible because of self-interference? Maybe the difference between the SR and XR is big enough that they don’t interfere with each other as much as 2 of the same models.

Joe

3

I would have to go dig out the conversion chart for the SR9 to be sure (we’ve been running them under v3 for a while, and it reports the actual channel so I don’t remember) but yes you are correct for the XR9, and probably correct on the SR9. I believe they have them posted on ubnt.com if you want to confirm.

Note I have not done ANY link testing of the XR9’s yet; I just got my test radio’s 2 days ago. I have talked to Mike at Ubiquiti about co-locating them and his response is that due to the difference in modulation it is impossible for them to see each other as anything other then noise on the channel.

You can co-locate them with probably about the same amount of luck as any other radio on the same or overlapping channel. it’s not that they can’t function, but the performance will degrade accordingly, and given the SR9’s proclivity to interference related problems, it would probably be a rather poor idea to co-habitat them on overlapping channels (referring to noise not just channel boundary overlapping).

My earlier recommendations for channel selection and polarization were best practice suggestions only. You should always do testing to find out what performs best given your specific enviroment. However given a range of channel selections to work with, In general you’re better off following what I said, as it should on average have the least number of problems/better performance.

4

I’m having a strange problem and maybe someone can shed some light on it for me. I have a rebroadcast site which has a backhaul link in horizontal polarization using XR9’s in 12 dbi rootennas. This feeds another XR9 going to a 9dbi vertical omni about 10 feet above it. The backhaul uses 907mhz in 5mhz spacing, and the omni uses 917.

I have one client on the omni, and whenever any traffic passes over the link, it kills the backhaul.

It seems like it’s interference or something, but there should be a good 5 mhz of spacing between the channels and the radios are 10 feet apart vertically, and the rootenna is mounted 10 feet horizontally in front of the pole that the omni is on.

Does anyone have any ideas of what might be causing this?

Thanks,
Joe

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Hey ForePoint,
Do you have any insight for me about my post?

Thanks,
Joe

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Is your omni using 5mhz channel spacing as well? Have you tried switching the frequencies?

I wouldn’t use a 900 Mhz as a backhaul unless you absolutely had to. I do not know your circumstances maybe NLOS who knows.

7

Yes, they are both using 5mhz channels and it doesn’t seem to matter what frequency I choose, they still interfere. 900mhz is the only option to get signal into this location because of trees and lack of elevation.

On a different tower, I have 3 XR9’s running 120 degree horizontal sectors. One is at 150’, another at 135’ and the last at 120’, so they all have some vertical seperation. If I max out the card at 120, I see connections start dropping and ping times going sky high on the 150’ antenna, even using frequencies on the opposite ends of the spectrum.

Doesn’t make sense to me.

Joe

8

I hear the word - rootenna again - also omni - both of which I seem to be having problems.
I have a single omni at 100feet and a rootenna 1.08 miles away.
No connection.

Are pine trees really that big of a problem?

I’m putting up a 18dbi yagi today to replace the omni. Is more power a good thing in pines or more problematic?

Thank you,
Rod

9

isnt that pretty crappy for 900mhz? 1 mile and it is having troubles, How LOS is it>? Im curious about how far 900mhz can go because i have not yet tested this frequency, I will on my next AP but do not have any experience in it as of yet. Let me know how it goes please. -Jordan

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Have you got enough juice going into the RB? Our experience is that SRx/XRx being powered with less than 24v (RBxxx) or 18v (WRAP) will do just this :wink:

See http://forum.mikrotik.com/t/preamble-problem/20326/1

11

Sorry, Havent been on the forum much recently…

I would confirm this with Mike @ ubnt, but I have heard that while the cards will transmit in 5Mhz, they will listen in 10Mhz, so while you are not transmitting over top of the signal of the other radio, you may still be generating noise that shows up in the channel that the radio is listening to.

other then that, I can’t think of any reason for that to happen.