MikroTik

Hi everyone

I am proposing a sectored base station for 2.4GHz for a customer with 15.5dBi 90 degree sector antennas. They can't use 5GHz in that country.

If I have 4 sectors (90 degree antennas) and use non-overlapping channels (more than 5 apart, say 1,6,11) then there are not enough available in the 2.4GHz band.

Can I re-use overlapping frequencies on **opposite** sides antennas on the base station? If so, how far apart (m) minimum?

The antenna vendor does not show front-to-back ratio on the datasheet which we have for P2P antennas.

Anyone with experience building/using base sites like this, would appreciate feedback. Everything we've done so far has been 5GHz band where there are plenty of frequencies so there is no such problem.

Regards & TIA

My sugestion is to use 1,5,9,13 channel for sectoral use. Do not use same channel in sectoral distribution because of the noise that one antenna make to another antenna.

Thanks Blue,

That's really helpful. Just to ask (before I commit myself to a customer roll-out) have you (or anyone else) tested that on a live sectored base station?
Agreed it's not best to use the exact same freq on a base site.
I guess I'd put 1 opposite 5 and 9 opposite 13.

Best regards

Stephen

I have not tested that, but my friend has "planted" 4 sector antennas in every corner of an tall building and have some experiments with channels and the solution is as I said 1,5,9,13. Only problem is that some cards do not support 12,13th channels. Then U gotta use 1,4,8,11 BUT 1ch antenna is placed oposite to 4ch, and 8ch opposite to 11ch. And the distance in this solution is critical. On that building distance between corners is I think about 20meters... And offcourse, all cables go to one big refrigerator in the middle of the building and the computer is placed inside If you live here you will know what am i talking about

Hi Blue,

Thanks very much for that, I understand exactly what you are saying - we'll follow that advice.
As usual people on the forum are being very helpful.

Best regards

Stephen

Depending on the Front to Back Ratio of your Sector Antenna, you can use over lapping frequencies with a few modifications.
First, you will need to seperate your antennas both in the X and Y axis. The formula is basicly a min of 10 Lambda 41 Inches or 1.04 Meters.

Second, you will need to Place a Fariday Screen between the Antennas with a sold Ground lead to Ground.

Even if you use non overlapping frequencies, you should seperate your antennas to avoid trouble.

You can find more information at the California Internet Service Providers Assoc. Wireless Information system http://cispa.thesupernet.com and look in the white papers. Microwave white papers, mutual coupling of Sector Antennas

Mark Esser
Vice President California Internet Service Provider Assoc. Wireless and Broadband Division

Mark,

That is super helpful - thanks a lot -
We'll come up with some base site design rules and post them on our site eventually for others to use also.

Regards

Markon can U help me with this:

I have two antenas: 24db gird parabolic and Yagi 18.5bd. Both antenas are pointed to omni, and the distance is about 100m. Omni is working on 2442MHz. What should be the distance between those two antenas. I can move antenna on X axis, but i am limited in Y axis (about 50-80cm)... By your lambda calculation: 10*(300/2442)=1.22m. Is it enough to distance antennas 1.5m by x axis?

stephenpatrick do you have the option of putting seperating the four sectors into seperate SSID ... this would help with client management and at the same time compleatly eliminate your channel issues... the best feature of MT is the ability to support multiple radios so why not take advantage of it

Sure we use multiple radios with one CPU platform.

However, separate SSIDs doesn't solve the problem of RF inter-channel interference, with one radio upsetting the adjacent one, and reducing sensitivity hence range.

Another post on "roaming" suggests that same SSID actually has some benefits. I hope MT can improve roaming support in the future, there is a serious "unique feature" to score there against competition.
Some other OS/product including Proxim have enhanced roaming/mobility - but we all prefer Mikrotik

Regards

I am under the impression that frq hopping does eliminate inter ssid domain interference ... I have several installations all using the same channel with seperate ssid domains and have noticed no reduction in range, sensitivity or thruput?

What about Channel Filters?

sumthin like
http://www.rflinx.com/Filters/2400_UHQ_Filter.htm


//never used one of them
//don't work for/sell rflinx stuff

why not use chan 1,6,11 and .....14? then you will have no overlap.

there is a firmware "upgrade" for the Senao cards that will give you the 14th channel.

I run 3 X 120deg sectors and an omni on the same pole, works fine for me.

Hey many thanks for that tip-
Can Atheros cards be extended in frequencies in the 2.4 band?
We were going to use them everywhere in the network.

Regards

Jrslick22

do you know where I can get upgrade firmware for senao to enable 14th channel?
thanks

whats your email address?

Sorry for the late response, but I have been very busy here. The California Internet Service Provider Assocation is building a super large Microwave Internet Service for the State Capital. WHEN SOMETHING GOES WRONG I HAVE TO GO AND FIX IT FOR THE TECHS.!!!

Now the answer is this, if you are running in a horizontal polarization mode on your antennas, you can reduce the Vertical seperation in half and still reduce the parisitic attributes. There is a 20 db reduction between horizontal and vertical which will make up for the reduce spacing.

However, if you are running in the vertical mode the answer is no, use 10 Lambda.

The reverse is true for horizontal seperations.

Mark Esser
Vice President California Internet Service Provider Association.

He' guys

We almost completed a base installation with 3dualband 2.4/5ghz 120dgr sectors.

The idea is to run al 2.4ghz sectors on the same chanel and same ssid to support roaming, but got no experience with MT/atheros roaming

We already have a network with only Linksys WRT54G equipment in 6 towers connected via WDS (http://www.sveasoft.com) firmware.
and 50 WRT54G client users spreaded over these towers, and working great.

I did a test once with 5 WRT54G AP's in oure house on the same channel and with the same Ssid, all AP's connected via AP/WDS mode and OSPF routing.
Then i ran trough the house with my latop and USB wlan stick (e-tech) while downloading a big file from a internet site.
on the diaglights on the AP's i could see wich AP was taken, and surprisely it worked great, downloading the file never stopt while walking trough the house.
This little test showed me that the USB client just takes the strongest AP with the same Ssid and leaves the other AP's alone !

Another test outdoor showed us on the web gui from a WRT client ;

the other AP's in the neigberhood with the same Ssid/channel with their MAC adress and rssi strenghts,

also this WRT client connected to the strongest MAC/AP/rssi and worked fine.

So i dont see the problem with putting all 3 sectors on the same channel/ssid and suport roaming, i think things work the same with mobile telephone sectors (how are hanging above oure sectors)

but this week whe are going to test it in real live, so then we will know

comments ?

If you plan to install permanent clients on this location I cannot see anything but problems. Clients who's rapidly switching from one AP to another would case the APs to use a lot of time on this one connection - and it will downgrade the quality of your site.

I believe you would end up having problems once you start connecting a few customers.

Roaming with a few clients would probably work just fine, as your testing (running around the house hardly qualifies as testing IMHO) shows.

If you are interested in creating a large roaming network for mobile users, then I guess you are on to something.

Let us know how it works.

What about Channel Filters?

sumthin like
http://www.rflinx.com/Filters/2400_UHQ_Filter.htm


//never used one of them
//don't work for/sell rflinx stuff

Stephen, I too would recommend using band-pass filters. They will clean things up inside your AP. If your tower is going to be a building, don't worry too much about re-use of the same frequency on the opposite side. If it is a proper tower I would look very closely at the front to back rejection on the sectors you are purchasing.

Have a look at these: http://www.hyperlinktech.com/web/band_pass_filters.php but note that these guys are b4stards about replacements/returns and their work is not always perfect. (I have had to break open and resolder two of their 5.8 GHz amps because they would not cross-ship replacements)

The RFLINX Channel Filters are very Good, however you will need to compensate for their inseartion Loss. (around 4 dB). The CISPA WIRLESS LAB has tested these Items for a Long Time and found them to be very well built and well in spects.
The Hyperlink units are ok, they have a compensation amp built in, however their amp design is not very good, it often goes into compression and thermal run away conditions. Never feed the unit with more the 18db, Then amp the outputs.

Oure Base station with the 3 dualband sectors 2.4/5ghz is up and running but didnt had the time found to test the systems, but hope to put some info here after the weekend.
Is there actually someone here how has real experience with sectors on the same channel/Ssid or other setup ?

just an idea ;
The situation is that we don't have "live"clients connected to it this week(end) so i could do some test for all of us i think with the 2,4Ghz sectors.
(we don't use bandfilters)

i don't want to take over this trheat from you "stephenpatrick" but maybe this is a nice oppertunity to test some settings on sector based setup ?

So if youre with me, put up some testing sugestions for "this threat" with a 3xsector setup with CM9 1513 wireless cards.
and i see if i can test it this week(end)

How about setting channel mode to DFS(radar detect mode) on every Sector ?