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changeip
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Solving 20km wireless link issues

Fri Jul 17, 2009 7:44 pm

Okay guys, I've been on Mikrotik for years now and know it inside and out, except I don't have a grasp on wireless stuff completely yet. I just put up my first backhaul 2 weeks ago - 20km! Woo Hoo I tell myself.

433ah w/ XR5 on each end
PacWireless GD5W wideband grid dish, 28db

Ive been struggling over low signal strength since installation. -76 is the best I could get, with -80 being the average. That's horrible I tell myself, must be something blocking the signal, or these antennas suck. Well out of the blue last night, without touching ANYTHING for days, I see this:

Image

Excellent signal, -60db! Nothing changed that I have control over, so what happened? We'll some thoughts I wanted to bounce off the 'team':

1 - The data center side is on a huge roof thats metal, although I am 15 feet above it.

Image

2 - I am shooting over an air conditioning unit, as shown in the picture, but I believe I am 4-5 feet higher than it still.

3 - RadioMobile shows a good view of the link, about half way there is a community that I probably am just barely shooting over.

Image

4 - At first I thought I was just getting into the fresnel zone and was going to find another option. Now last night the signal increases by 20db and is giving excellent performance.

5 - Without even touching anything the signal is affected - but why ? My guess is that there is noise - but every single channel gives me the same results, if I can get connected on them that is.

6 - Noise floor before and after this is the same, -102db average.

Image

So how do I go about tracking down what's crushing the signal across the entire spectrum ?

One side is on a water tower, however moving 100 yards either way doesnt seem to help:
Image

And the other side on the data center:
Image

Any help troubleshooting would be appreciated.
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Re: New 20km link, weird interference.

Fri Jul 17, 2009 7:59 pm

I believe the Frequency Use tool is only showing you 802.11a frames received. It does not measure raw energy received at the antenna like a spectrum analzer would. You could have an interference source and not know it from that tool. You could hook up a real spectrum analyzer to see what noise you might really have; however, you said it's consistent performance across all the channels, so I doubt you have interference across every 5.2, 5.4, and 5.7 channel (it's possible just not probable).

Given that it suddenly changes and if you see that sudden 20db change on all channels, you should look into the equipment. I'd check the pigtails and coax. Also, I'm not a fan of those antennas for backhaul links (much prefer Radiowaves or Andrews parabolics).
 
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Re: New 20km link, weird interference.

Fri Jul 17, 2009 8:00 pm

BTW: GREAT posting. Lots of clear data, good descriptions, graphs -- I wish everyone posted like that. Very professional.
 
changeip
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Re: New 20km link, weird interference.

Fri Jul 17, 2009 8:25 pm

yeah im tired of posting like 'my signal isnt good, help me' : )

I did order a completely separate rb433ah with an XR5, exact same setup - but portable enough for me to drag it around for testing. I got the same results using the test setup 100 -200 yards away (on the water tower side). I think that would rule out bad hardware / power at the one site, and I am going to do the same on the other side this weekend. However, if one side was bad wouldnt the signal tx / rx be way different if it was only 1 side with the problem ?

It is 20db across the entire spectrum, which makes me wonder if it's the air conditioning on the roof that stopped working, or a massive power line thats in middle that went out or something. I am using horizontal polarity, I am going to try vertical in the next day or two as well.
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Re: New 20km link, weird interference.

Fri Jul 17, 2009 9:11 pm

However, if one side was bad wouldnt the signal tx / rx be way different if it was only 1 side with the problem ?
Not really. What if the pigtail at the data center side is a 20db attenuator? Wouldn't that affect tx/rx at the same time? If you had highly asymmetric signal levels, then you would start to look at the card(s).

You didn't mention lightning arrestors. Are you using any? If so, try swapping it out for a pass-through.
 
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Re: New 20km link, weird interference.

Fri Jul 17, 2009 9:23 pm

Currently it is the built in cable from the GD5W directly to a MMCX / N pigtail - no arrestor or LMR in there anywhere yet. The radio is directly mounted behind the antenna so the cabling is very short; I thought that might interfere as well, but why would it get better for just 8 hours and then go back to the way it has been since installation? If it was cabling would I possibly see that signal increase for 8 hours and then back to what it has been doing ? I won't rule out the cabling / hardware until I test both sides with another unit, but I'm leaning towards something outside of my control causing this. Just trying to figure out how to pin-point it. Thanks for your input too : )
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Re: New 20km link, weird interference.

Mon Jul 20, 2009 11:54 am

It's not a problem from pigtail, or connectors; I had the same problem, there is problem regarding the propagatin; I couldn't find a fix, maybe replacing with bigger antennas or/and changing polarization; sun also causes to loose signal. In my case also when it was cloudy the signal was excellent or during nights.

good luck
 
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Re: New 20km link, weird interference.

Mon Jul 20, 2009 3:16 pm

Great post changeip!
Looking at radiomobile it seems you have your fresnel kinda messed up but try to put the correct values of antenna height maybe it's not that bad once u set at around 15-20 meters the antenna over the roof of that building..
And i experienced the same problem on links over the sea ( http://forum.mikrotik.com/viewtopic.php?f=7&t=25362 ). I almost fixed it raising a little the azimuth of both antennas, losing few points of signal strenght but avoiding a lot of those problems..
Also i suggest you to do a backup link in another frequency... it should solve you all the problems i guess..
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Re: New 20km link, weird interference.

Mon Jul 20, 2009 7:51 pm

The signal strength is the signal strength, regardless of interference. Interference changes the SNR, and interference isn't so easy to reliably measure.

I would suggest pigtails, cables, feedhorn changing/swapping, etc... We've seen feedhorns go bad on grids and dishes where the signal is usually weak but intermittently good. This has happened to us with Pac Wireless and Gabriel feedhorns. You might have started off with a feedhorn that is mostly bad. If you have a spare antenna, borrow that part or antenna to test.

It is possible the shape of the metal roof causes some destructive multipath interference at times. You would have to temporarily move the setup to a place where it didn't shoot over the metal roof, but other aspects were the same to test this. Some metal roofs do affect signal, but it's really hard to predict.
 
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Re: New 20km link, weird interference.

Tue Jul 21, 2009 5:47 am

Sorry JP, but that is not necessarily true.

Reflections can be strong enough to cause the LNA to become saturated causing the low signal strengths.
Metal structures can be troublsome.
Try lowering the Output power and see if the receive strength increases.

Metal distorts magnetic fields.
Microwave can be viewed in a simular manner, in which the field can and will be distorted by nearby metals.

Not to mention any evapoartive effects from the metals heating and cooling.

(Have you ever tryed a radio shot over loadstone?)
 
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Re: New 20km link, weird interference.

Tue Jul 21, 2009 7:06 am

I thought I'd mention... the signal has sucked for at least 3 weeks, but it has been VERY consistent. -80db almost all the time. However, that one evening it went from -80 to -60 and then back again after about 8 hours or so.

Tomorrow I will be testing an entire new setup on the data center side to see if its hardware / antenna. Will post more info w/ more pics shortly.
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Re: New 20km link, weird interference.

Tue Jul 21, 2009 9:30 am

I also have 25km link with similar behavior. Night sometime signal goes to -69 usually is -80 but sometime goes to -90 and drop. But I possible have problem with fresnel zone one of antenna is not very high.
If you find what cause this please write here.

First setup I use R52 card and latter replace with R5H with R5H work better sometime drop but establish very quick.
 
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Re: New 20km link, weird interference.

Tue Jul 21, 2009 9:39 am

It might have something to do with temperature changes within the path.
 
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Re: New 20km link, weird interference.

Tue Jul 21, 2009 10:32 am

I had the same problem and would like to ask you if the signal was increasing when it was cloudy on both sides?
First I used for this link SR5 with dished of 85cm and the signal was -81, throughput 28Mbps and then replaced with XR5 and dished of 120cm and the signal increased to -77. Use only dishes(offset) for backhaule because it works well even when interference is present.
 
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Re: New 20km link, weird interference.

Wed Jul 22, 2009 7:56 am

Not to mention any evapoartive effects from the metals heating and cooling.

(Have you ever tryed a radio shot over loadstone?)
Sounds like a problem I've had here.

I've got one customer who only lost signal between 2:30 and 3:00 PM, usually for under 10 minutes, same time, every day.

The heat coming off of the roof of his house was causing the problem. Once the sun went down, the problem disappeared. No problems at all during the winter. Still need to raise his antenna a bit, but apparently the system is more resilient than it was in the past.
 
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Re: New 20km link, weird interference.

Fri Jul 24, 2009 7:32 pm

Okay, some updates.

Image

Yesterday I changed out the data center side completely. New rb411ah, XR5, antenna, cable, pigtails, etc. I also made a point to swap over to vertical polarization (from horizontal) to see if that helped.

1 - I gained a db or two during the horizontal to vertical change, however I think that's probably because of the extra effort during alignment. Still sitting around -78 to -80 very steadily.

2 - Antenna alignment on horizontal was 10x easier... in vertical I really had to get it within a few millimeters turn to get it locked on. In horizontal it seemed like I could move the antennas 3-4 inches either way and still be connected.

The link has been up for 3-4 weeks now. It has been right between -78 and -82 the entire time. Only 2-3 times has it magically gotten perfect, -60db for about 4-8 hours each time.

Some thoughts, tell me if I'm way off on any of these:

1 - the freznel zone has nothing to do with this (directly), otherwise I wouldn't see it all of a sudden get better (unless some obstacle in the fresnel zone all of a sudden moved).

2 - the freznel zone is indirectly related in that when the weather has effects (temperature inversion, fog, atmosphere)it helps the overall freznel zone effect. Rather than weather affecting it in a worse way it might be making it better? I can't confirm it was weather when it got better, but that's my guess.

3 - I'm shooting thru a high voltage powerline about 0.5 miles away, is it possible thats affecting it? Maybe the power on that line was turned off that time it got better? I wouldn't think so, but just a long shot.

Both sides have been replaced independently. Each side was moved 100 meters to the side with no changes.

I'm somewhat at a loss at what to try next. I do know that with the existing hardware and link path I have gotten -60db, but what options do I have to try to keep that as the normal strength? If I change out antennas for dishes is that going to make any difference? If I raise either side 10ft (on a 20km link) would that help much? Should I switch to 2.4ghz? I assume that will make the freznel zone larger...
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Re: New 20km link, weird interference.

Sat Jul 25, 2009 5:56 am

changeip,

Try lowering your tx power in half at both ends.
Check rx strengths again.
 
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Re: New 20km link, weird interference.

Sun Jul 26, 2009 8:33 am

okay, i did test that just now. changed the setting to 'card rates' and then stepped down a little each time (on both sides at the same time).

xr5 card rates:
20 - 86db-88db
22 - 84db
24 - 82db-83db
25 - 80db-81db
26 - 77db-78db
27 - 76db-77db

any lower than 20 and i couldn't get a link at all.
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Re: New 20km link, weird interference.

Sun Jul 26, 2009 8:22 pm

Sam..

You said that the signal for better for 4 - 8 hrs at a time,,,,

The data center ( am assuming Sandiego L3 ) follow me here...

Dont they use DC rack equipment... Isnt there a LARGE btty UPS... system... (charging system and inverters)

Also, the other antennas on the platform..

What I am getting at... is is ther a chance that you could look at the schedual that the signal improvovrd, and see of one of the other systems in the area (eather sise) went off line for maintanance , schedualed or not,

I am NO wireless expert, but the timming sounds "interresting",, 4 then 8 her usualy at 10:PM or so...

It would possably allow you to find the source by "connecting the dots" if there was a maint outage of a system, then find out when it will be down next or if "crashes" when it did and match it to your graphs... Then smite the offending pice of equipment with a few well placed hammer blows.. :D

I think I would wander down that road for at least a short while,,,
Things that make you go "Hmmmmmmmm"...

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Re: New 20km link, weird interference.

Sun Jul 26, 2009 9:48 pm

Looks like propagation effects, not interference.

I did some multipath calculation and the expected signal at the receiver, for 28dBi antennas and 23dBm TX should be -56dBm. At this distance even over sea surface, same antennas, the SLA is 99,99935% (e.g. 4 minutes total outages in one year). As your RSL is -80dBm ... the fresnell zone obstruction at the middle of the path can not be neglected.

Since the modulation is OFDM I think that multipath desctrutive atenuation is out of question because this kind of interference is mostly narrowband so you miss some OFDM carriers but the avereage received power must remain the same (except if there is several paths with different time delays but the terrain seems pretty mixed).

Along the day when there is not any significant changes at temp X humidity in the valley between the mountain and the obstruction the signal still stable. But after sunset or just before sunrise (e.g overnight) some ducts can show up, acting as waveguides or reflectors, making the beam change its direction or elevation. This can exist durying the day, depends on the local weather.

The obstruction at the middle can create something called knife effect too, e.g. bending the beam downwards (good if you have a probe receiver some meters down hill :D).

And looking at the antena place at the building ... microwaves does not like very much big surfaces in front/below the antenna (the metal roof, a mirror). Sugestion: assemble anoter rig at this metal roof edge and take some RSL readings. I had some trouble once at 2.35GHz STL from a TV ENG van which was assembled in the middle of the van roof. Depending on the parking position the signal desapear. One (1) meter movment and lots of signal show up.

Regards;
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Re: New 20km link, weird interference.

Thu Jul 30, 2009 10:19 pm

Regarding your height above the roof... Traditional microwave theory states that a 22 degree plane exist between the radiator and the edge of the roof.

I've 'fixed' many troublesome links where other companies have installed the equipment to close to the roof and simply moving it to the roof line nearest your far end corrected the issue.

Horizontal polarity is also more susceptible to multipath reflections off near-field objects such as a roof.

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changeip
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Re: New 20km link, weird interference.

Mon Aug 03, 2009 9:21 pm

I am starting to think its freznel zone effects as well, but really can't figure out why it would increase tremendously every once in a while:

Image

If it was the roof reflecting would it do what I see above?

If it was the weather (temperature inversion) would I see it only happen for 30 mins or so as shown above?

Now if it was another source putting off RF interference I would see the above. Is there an easier way to test that / track it down?
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Re: New 20km link, weird interference.

Mon Aug 03, 2009 11:23 pm

I think only a spectrum analyzer would most likely help and show the RF interference levels, if any, as I have a few doubts about the interference theory. If it were RF interference, then changing your polarization would show different SNR levels. Have you checked that? Have you tried any other cards besides XR5s? Have you tried other boards? Have you checked both sides close to each other in a controlled environment and compared the results with other working units?

But I strongly believe the answer is really simple and the most obvious one. I think you have underestimated the middle community height and that those excellent signals you receive every now and then, are only the results of some type of passive reflection somewhere in the community every now and then.
 
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Re: New 20km link, weird interference.

Tue Aug 04, 2009 12:03 am

yep, agreed. Suppose it is truly freznel zone getting me, is there anything I can do to improve my situation? Bigger antennas - circular polarization - Wireless N - ? I know I have gotten near -60db signal at times, so there must be something I can do to get that to be more stable... I hope :)

I have replaced the radios completely, both with XR5s each time, but same results. Swapped from horizontal to vertical, etc.
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Re: New 20km link, weird interference.

Tue Aug 04, 2009 2:16 am

Well, searching that community in the middle and finding the surface that reflects those waves and keeping it that way, is one way to go!

Seriously though, N will help if signals are reflected but in your case I doubt if it will help much. Increasing gain in general (TX/RX, antennas, minimize losses) will definitely help but I would personally research a bit more the height factor. That seems to be your whole problem and you should focus on that. It should be easy with a good GPS to measure the community's height and the 2 remote points as well as the distances and figure out if it is the fresnel zone you are dealing with here. If you are within the fresnel zone, and not way below it, moving the antenna around and/or lifting it a few meters at both points will definitely help, otherwise, an active repeater with good visibility to both points may be a better, in many ways, alternative.
 
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Re: New 20km link, weird interference.

Tue Aug 04, 2009 7:11 pm

Thanks for everyones input, I appreciate it. I know it's helping me narrow it down and get this fixed.

Image

This morning it did it again - the past 2 weeks have been very steady around -80db. This morning I see increases all the way to -60db it looks like.

I can rule out that roof being a problem, correct? The roof hasn't moved since I installed it : ) I did move it about 50 feet forward with the same result but didn't get quite to the edge of the roof. I will try this next time I am up there.

I think I can rule out that its my rb433 or xr5 cards. I've swapped both sides and get the same result.

I can't quite rule out that it's a weather effect. It is hot as heck here (and more humid that normal), but it has been for a while. I think I might talk to a weatherman around here to see if they can correlate this mornings signal increase to weather... Typically I would think the weather would make the link worse, not better however.

I will take some GPS readings at 3 sites, the 2 ends and the middle. I can visibily see each end on a clear day, 20km away... it is barely skimming that community in the middle, but still clears it by 20-40ft I would think.

My question now is - if there is something in the freznel zone causing interference, would that affect my 2 endpoints? Imagine I am shooting over and R&D company's building that is performing high powered RF or 2 way satellite communications, would that affect my path in the middle of a 20km link ? Part of the path is a military base, maybe there is something interfering on their land?
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Re: New 20km link, weird interference.

Thu Aug 06, 2009 9:07 pm

I'm starting to think it's the fact I'm shooting within a few hundred yards of a doppler radar ball in the very middle of my link. I am reading that weather doppler sends out 1cm - 10cm wavelengths. 5ghz wifi is about 5cm right? I also realized that the FCC mandates DFS on 5ghz links because of the radars? Does anyone have any experience with a doppler radar interfering with signal?

Image

Really makes me wonder if those increases in signal were when they were doing maintenance or changing parameters on the doppler. I even heard the weatherman on the local news a few nights ago say they were going to fine tune a few things to see if they could detect different size water droplets. Hmmmmmm.

I'm going to swap the 5ghz antennas and XR5 cards with the 24dbi PacWireless grids and XR2 cards today and see what happens...

And a picture from the other side:

Image

Could this radar theory explain why the signal on every single 5ghz frequency is around -80db, and when it has it's moment and is good every single frequency is good again?
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Re: New 20km link, weird interference.

Sun Aug 09, 2009 2:33 am

ChangeIP,

I really believe your question has been answered by nramos. I see this all the time on my longer links, except the periods of better than normal signals are usually followed by signals 10-15 dB below normal or in your case a -95. In my area this mainly happens at night or early AM and only when there is absolutely no wind blowing. I need to have a signal in the low to mid 60's to provide enough fade margin for a 99.9% link in my area. Hams call this 'thermal ducting'. Hot and cold pockets of air acting like a conductor. Signals get crazy good when both your antennas are in the same layer of air or 'duct' and when one of them is above or below the layer of air(duct) you are sucking mud. :-)

If this were my link I would try increasing the gain on the antennas first and then possibly height. I've tried the antennas you are using, they are not even close to the gain of the Pac solid 28 dB dishes. I would recommend the Pac 32 dB antennas or at least on one end of the link and a Pac 28 dB solid on the other end. The antennas suggested earlier are very good quality, I'm just telling you what I am familiar with. The Pac 28 dB grid I tried seemed to be more like a 20 dB in the real world. I do use the smaller grids sometimes for links less than 3 miles. Good luck!

You've helped a lot of folks on this forum and I thought I would toss in my two cents to try to help.

Good luck in the RF world.
 
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Re: New 20km link, weird interference.

Sun Aug 09, 2009 5:05 am

The Pac 28 dB grid I tried seemed to be more like a 20 dB in the real world.
Really? I have a few in the field and they do seem to be in the 28 dB area.
Either that, or the 24 dB panel antennas are really 16 dB.
 
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Re: New 20km link, weird interference.

Sun Aug 09, 2009 6:28 am

Really? I have a few in the field and they do seem to be in the 28 dB area.
Either that, or the 24 dB panel antennas are really 16 dB.
Maybe 20 db is an exaggeration on my part. I replaced a small 24~25 dB dish with one of the 28 dB grids when they first came out. After realigning for quite some time with no better than a loss of 4 or 5 dB I finally took the grid down and put the dish back up on the tower. A few weeks later I replaced the small dish with a Pac 28 dB dish and saw a slight improvement instead of a loss. This was a 19.5 mile link. These antennas had just come out, maybe I had a bad one........
 
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Re: New 20km link, weird interference.

Sun Aug 09, 2009 7:29 pm

Image

BTW ... the RSL when those humps happen are vy close to the calculated RSL as if there is no obstruction at all. Ducting here are common and sometimes makes signals on 1296 or 2304MHz travels 600Km+ inside them.
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Re: New 20km link, weird interference.

Mon Aug 10, 2009 3:35 pm

sorry for interrupting, but this thread is super useful! keep it up guys!
No answer to your question? How to write posts
 
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Re: Solving 20km wireless link issues

Mon Aug 10, 2009 5:47 pm

sorry but i think your problem is the Fresnel zone
i have link of 16 km, first i set the power at 28dBm and the signal strength was about -40dBm then i decrease it to 100mW 20dBm to set the signal strength at -60dBm,
so you must have the power signal receive at least -55dBm.
try to set another point between the two tower
 
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Re: Solving 20km wireless link issues

Mon Aug 10, 2009 8:04 pm

I think mramos is correct possibly. I will be replacing the system with XR2 cards and the 2.4ghz grid dishes today or tomorrow to test things on another frequency, I need to be sure it's not the doppler radar I am shooting thru causing the problem.
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Re: Solving 20km wireless link issues

Tue Aug 11, 2009 2:39 pm

A solve is to use dishes of more dBi or/and to rise-up your antennas; I don't think if you do some settings you will gain more signal. If you use 2Ghz you will get a lot of interferences; I would try 802.11n (with 2xpair of separate atennas) that works nearLOS
 
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Re: Solving 20km wireless link issues

Thu Aug 13, 2009 9:20 am

How is the 20km link doing now? Any updates to this useful thread?
 
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Re: Solving 20km wireless link issues

Thu Aug 13, 2009 8:00 pm

I'm trying to be thorough in testing, so I did swap out both ends with XR2 cards and Pac Wireless 24dbi Grid Dishes. It's been running since yesterday so not enough time to see if those increases of signal happen sporadically.

Image

The noise floor on 2.4ghz is way worse than 5ghz, but I am getting about the same results. Poor signal - 85db or so. I didn't think a different frequency would help, but I had to test that just to be sure.

This picture was taken from directly in front of the grid dish and shows that I'm shooting over the AC handlers by a few feet. They are about 50 feet in front of me. I tested walking to the front edge to get out of the way and I get the same result, so I don't think it's those. The white arrow shows where it's aimed - just barely above the hillside.

Image

Here is a zoomed in shot, white line is where I'm shooting, the black arrows are the doppler ball and trees you can see from the other side. I am shooting very close to that doppler, and still have thoughts it's what's causing me problems:

Image

Image

That doppler ball is HUGE!

Anyhow, my next test will be to go up the mountain higher on the non-data center side. I don't have permanent mounting options there, but just to test.

Sam
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Re: Solving 20km wireless link issues

Fri Aug 14, 2009 2:32 pm

I hate those PW Grids
If you have some handy, try some panels, they seem to preform better for me when Fresnel is a problem.
 
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Re: Solving 20km wireless link issues

Fri Aug 14, 2009 3:55 pm

If the test in the mountain is satisfactory, I would put a tower together with the datacenter of approximately 24 meters. With antirotation star.

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Re: Solving 20km wireless link issues

Fri Aug 14, 2009 8:23 pm

I have been reading this thread and looking at the Radio Mobile path. From My experience in using Radio Mobile, I see the major problem is the obstruction where most of the lower half of the Fresnel zone is blocked. Radio Mobile is showing you the expanding Fresnel zone with the dashed white lines around the direct path. That is why Radio Mobile is so good. It is predicting a -85dB signal level so is close to what you are experiencing. The occasional bursts of good signal is indeed a ducting effect from cool to hot transisions or visa versa.

In my opinion, the ONLY fix is to get both ends much higher or put a repeater at the obstruction so you can "bend" the signal so to speak.

I have had 5 gig links of about 15 miles that ran well most of the time, then went bad for a short duration of an hour or so, mostly during the Spring or Fall seasons. I did as someone posted, increased the gain of the antennas to get above the weakest durations. Once that was done, the problem almost never occurs.
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Re: Solving 20km wireless link issues

Sun Aug 16, 2009 6:55 am

If you think your link is odd, consider this image for a 1.5km city link with perfect visual LOS:
Image

As you can see, it regularly goes from between -50 to -70.
 
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Re: Solving 20km wireless link issues

Thu Aug 20, 2009 2:05 am

Hello,

Please tell me where do You generate that nice signal graphs?
http://www.mreza-wisp.ba/
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Re: Solving 20km wireless link issues

Thu Aug 20, 2009 4:14 pm

Hello,

Please tell me where do You generate that nice signal graphs?
I use mojiro's cacti template from http://forum.mikrotik.com/viewtopic.php?f=2&t=21189
 
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Re: Solving 20km wireless link issues

Thu Aug 20, 2009 8:57 pm

I use mojiro's cacti template from http://forum.mikrotik.com/viewtopic.php?f=2&t=21189
RK, thanx...
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Re: Solving 20km wireless link issues

Sat Aug 22, 2009 10:16 pm

Maybe try looking at the problem upside down, in so far as, your signal of -80 was the norm (all be it less than expected)

And that the periods of -60 are from times of signal enhancement.

The terrain looks like a candidate for temperature inversions. You can spot the phenonema crudely when smoke from a stack ceases to rise but drifts horizontally.

Temperature Inversion also preludes ducting another phenonema affecting VHF, UHF and less commonly Microwaves.

Maybe it was raining somewhere in the path those days, or there was high humity, causing refraction and then multipath.

What about a car that was parked somewhere in that link, that may have caused a mulipath affect, causing the signals arriving partly in phase to add.

Anyhow, interesting thread.

Best of luck... Simon
Last edited by wirelesswaves on Sat Aug 22, 2009 10:45 pm, edited 2 times in total.
 
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Re: Solving 20km wireless link issues

Sat Aug 22, 2009 10:29 pm

http://www.ips.gov.au/IPSHosted/NCRS/wa ... erans1.pdf

http://sirkova.com/documents/ICEST_2003 ... tances.pdf

http://www.its.bldrdoc.gov/pub/ntia-rpt ... hap1-3.pdf

http://www.dxinfocentre.com/propagation/tr-modes.htm

Some of the above links are tiring reading, especially the third. For 30 years I played around with VHF communications, exploiting the uses of all known propagation phenonema, including meteor scatter and moonbounce.

Maybe as I suggested, its not equipment related in any way, just that the freznel zone has given you less than your first expectations, and on the days of 20dB extra, your signal is actually enhanced.

The last link is the simplest explanation from us radio ham chappies

73's EA5/G0MGA
 
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Re: Solving 20km wireless link issues

Fri Sep 18, 2009 3:36 pm

Those power lines in the image you posted can also create anomalies.
They will also expand and contract with temp fluctuations, etc.

My beleif is that there is not one or two things, but several things, all working against you on this shot.
 
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Re: Solving 20km wireless link issues

Fri Sep 18, 2009 4:02 pm

THE MACHINE IS AGAINST YOU!
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Re: Solving 20km wireless link issues

Thu Sep 24, 2009 11:50 pm

biger dishes - beter signal ;-) simle as that ... with two 90cm solid state, and some LOS ... there is no way of having any problems on 20km ;-)
 
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Re: Solving 20km wireless link issues

Fri Sep 25, 2009 9:09 am

have you tryed moving your link o the front of the roof so that you cut out the noise on the roof?


so your 20km link becomes 19.7km


i always try keep my anntennas close

and another thing whay power are you using ups power and 12v or 48?

just a question i did not see any answers to
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