How to deal with interference

I’ll like to start this thread so we can talk about the different ways one can deal with interference on Canopy. i.e.: changing polarity, physical separation from the source, using different bands, etc. What kind of interference you ever had? self interference or from an outside source. How did you deal with it?

I’ll start

We use all 5.7 Advantage AP and Mixed SM all in 5.7
Right now we have a site where most of the non-overlapping channels are being interfered with. Only 2 of them are available. We are thinking on changing this APs and make them horizontal pol. We know about the stinger that can change polarity on the SM but we don’t know what to do with customers who have reflectors. How do we turn them around without exposing the radio to moisture and without having to seal them everytime

I don’t seem to find a lot of other people who had to deal with interference on the 5.7 band so I was thinking we could start a thread on the subject to help us now and for future reference

Thank you

Great thread topic! I can’t speak to your particular issue, but we have an issue that belongs in this thread. We’re in rural (read flat with lots of trees) Central Illinois, and so we are using 900MHz for last mile. We use 5.7 BH sets and a 5.7AP with an omni for the close remotes. We have no trouble in our 5.7 area, but we have constant noise everywhere I point in the upper few frequencies on the 900MHz band. So, we are limited to two of the three non-overlapping bands. We deal with it by not dealing with it. We have tweaked around and just can’t make an AP stable in the top 900MHz channels, so we are re-using the two lower non overlapping channels. We have weather doppler less than a mile from our main AP site (the one with about 45% of all our radios on it), but the only direct problem we’ve seen with that is when we have attempted to point right past it.

This problem has ruled out going to three 120deg sectors as I had originally planned for the primary site, so I’ll just be adding another AP with an omni.

Anyone have any ideas about what might be crowding the top edge of the 900MHz range throughout our whole county?

I too notice the 925-930 range being used constantly. I had suspected cell/cordless, but have not followed up. It was interesting when I picked a baby monitor up in a house on 915 about 1/4 mile away…

Alot of paging equip is in the 900 range as well, so thats something to watch for.

Just a re-post
We have a few 900mhz customers having problems dropping the connection. Most are LOS and high on the landscape. Where others on the same AP are having no problems. The ISP has tried adjusting the frequency with no results. Location is 100 Km East of Perth Western Australia.
Any Ideas what we could do to prevent the interference?
Please follow this link for details and spectrum analysis.

cvs wrote:

This problem has ruled out going to three 120deg sectors as I had originally planned for the primary site, so I'll just be adding another AP with an omni.

MTI does make a 180deg Horiz Pol 900MHZ antenna now. I have not tried it out and am not sure if it would work better than adding a second omni, but it is a sector antenna and might be a better option for you.

We are planning a site where we want to cover a full 360 but not use an omni either. Our top band is also completely swamped. We have decided to put up 4x 90deg sectors using 2 frequencies. Our area is sooo covered in large pine trees that we use 2.4 for backhauls because we cannot get LOS on almost any connection.

CVS go back to you’re original plan of 3 120’s with 3 separate AP’s I promise you will be happier. An omni with a single AP has to deal with interference from all directions. unfortunately the SM’s on the side of the AP that has no interference suffer. A AP might be able to deal with the interference better if it does not have to listen to everything out their. I have seen the noise floor decrease by 10 db when switching from an omni to 2 or 3 120’s.

attitude0330: If I do that, then I basically lose 120 degrees worth of clients to interference, don’t I? That’s why I’ve not pursued that before. We’ve basically got about -65dB of pretty constant signal in that upper end of the band. The best idea that I’ve seen so far is mattmann72’s, to use a couple 180s…

I would agree with Mattman.

If you look at the standard setup of AP’s, generally you will share the same freq with AP’s that are back to back.

So if you only have two freq’s, then 4 90’s would be the answer with freq #1 was N/S, and Freq #2 was E/W. If you only had one freq, then an Omni, or two 180’s would be the answer.

Of course the equipment used should scale to the # of subscribers.

You could use 2 180’s, 3 120’s, 4 90’s, or 6 60’s however you decide. My point is the narrower the antenna, the less interference the AP has to deal with. If you use 2 180’s you might lose one 180 to interferance. The interference might be from all directions, or might be from a single direction. An omni wont help you narrow it down. The source could be for example a FM radio station STL point to point link it is possable that it could only really effect 60 deg of a 360 deg sector. I don’t expect everybody to be able to go out and buy a $30,000 spectrum analyzer like we use, but radio is our main business so it’s justified. When I plan on setting up a new POP the first thing I do is analyze the spectrum to see what is out their and where it is from. You too can do this using a SM, but dont use an omni. Look at the spectrum using a 60 deg view and take 6 diffarent readings. You might end up being able to use the upper band after all.

I agree with you that the narrower the antenna, the better a system can/will perform. Having an omni, or 2x180’s can limit the ability to combat interference.

However, these guys have already established that there is interference limiting them to only 2 of the 3 possible channels. In this case 2x180’s or 4x90’s will provide the maximum density with the least self interference.

Downside…New interference in one of the two remaining bands could be a killer.

What is the nature of the interference you are seeing from FM STLs? These belong in the 950 MHz band, of course, and don’t (in my market) stray into unlicensed range.

Jerry I agree with you 100% im just making sure that they are not relying on the omni already at the site to give them a proper picture of the spectrum. If you are installing an omni at the location by all means use an omni to determine what channels are avaliable, but you dont want to rely on the readings from the existing omni to implement sector antennas. Chances are you can use the third channel on an AP that is 180 deg from the direction of the interference. and yes it is possable the interference is omnidirectional.

We have checked by all means imaginable (by me at least) to locate the directionality of the interference, and have come up with nothing. Everywhere we point we get the same levels of noise in that upper band. I really like the 4 90deg sector idea, should have thought of that one myself.

Thanks for a great discussion, everyone!

Is the location co-located with other radio equipment?

We have had to deal with utility companies using 900 on telemetry in certain areas. Only having 3 channels really sucks.

Actually, we have 6 locations throughout our county. Still can’t pin it down.

:cry: :evil: :?

Funny enough, in those cases where we had a hard time finding the interference source we have always ended up discovering it is in the same building/tower were we are at. Sometimes is small equipment that blends in with the rest of the stuff mounted on the building/tower. Look carefully. We once spent about a week, 8 hours a day dedicated to finding this radio that was messing us up to finally take a better look at the building we were at and found a proxim 5.7 ghz 10 inch by 10 inch in size, installed right in between two A/C units. As far as antennas go, does anybody know who sells 180 panels, 5.7 ghz? had a hard time finding those. Has anybody tried the new H pol stingers? We use 120 deg cyclones in all our sites and we are trying to find a way to H pol some of them

I had the three 120 degree sectors and lost the top of the band also. The solution to this was to get 4-90 degree sectors and run the lower channels back to back i.e. 906 and 915. Well, I’m on top of a cylinder shape water tower and now I’m getting back to back self interferance between my ap’s. I shut down all my ap’s changed one to an sm and did a spectrum analasys. The noise floor was minimal. Then I turned on the ap directly to the back of it and did another analasys and the noise floor was pegged out. So now I’m building brackets to mount the antennas on the side of the water tower and hope it works!

Baby Monitors are evil with 900MHz… If you go to the customers SM, and can’t even see the 900AP in “AP Eval” tab, then you have heavy localized interference. Ask the customer to not use one, and maybe the neighbors could turn theirs off when not in use.

This inteference thread is great.

We have recently started having intermittent interference on the 915 band.

We lose 10 of the 18 SM’s on that particular AP.

Every SM that normaly is in the -62 - -70 range gets knocked off.

Those with a stronger signal do not drop except the one or two SM’s that are usually in the -55 range.

Is it safe to say that the SM with the strongest signal say, -55 jitter of 1 thats gets knocked off is close to the source of interference?

This just started this past Monday.

So far, its hits around 7:30 AM for 1 hour. Then again around lunch, and again around 4:30 PM.

We were ready this morning for the 7:30 interruption, with a couple of SM’s in the field running the spectrum analysis, but wouldn’t you know, it did not happen this morning.

Any suggestions would be appreciated…