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spok
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60km link ?

Sat Dec 03, 2005 11:19 pm

Please tell me some info about 60km link..
- possibility
- signal & nose
- performance
- influence of ran, fog ,snow

I will use router bord 532 + Super Range 5 400mW 802.11a + HyperLink Parabolic Dish Antenna 29 dbi 5,8 Ghz....

link1(480 m) -------------60km LOS----------------link2(80m)
 
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acim
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Mon Dec 05, 2005 2:10 am

You should search this forum, people reported successfull links over 120km. If you have perfect line of sight and rural area between the points, this should be no problem. I have to install a bit shorter link soon, something like 30km and I plan to use exactly the same equipment as you noted. Just maybe grid antennas instead of parabolas because of less wind influence. Parabolas should be better regarding signal, of course. You should expect something like 8, maybe up to 12 Mbits of real transfer, but you never know.
 
spok
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Mon Dec 05, 2005 9:39 pm

Hvala...
Odakle si? Neki kontakt...
 
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acim
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Mon Dec 05, 2005 10:04 pm

Moja email adresa je acim na linux tacka co tacka yu

Sorry to other non-Serbian speaking guys, I just wrote my email address because there is no private message option.
 
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djape
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Tue Dec 06, 2005 11:00 am

I use satellite dishes with feeds for 30k link and I have ~10mbit/s

Cheers zemljaci :)
I drink like a pirate and smoke like a hippie...
 
chucka
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Tue Dec 06, 2005 8:49 pm

I would at least use the 32 db dishes. I have one link at 32km. I have occasional dropouts, maybe 5 minutes of down time per month(-62 to -68 typically). This is with a 29 on one end and a 32db on the other. I plan on upgrading the 29 to a 32db dish when I can. This link was originally two 29db dishes and it was probably 15-20 minutes of downtime per month(-68 to -74 typically). Use the MMCX connectors or at least don't use the tiny gray pigtails! Fog or rain has not caused me any problems. My links give trouble during a crystal clear night when there is no wind.
 
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acim
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Wed Dec 07, 2005 12:23 am

@chucka

Hmm, strange. On the sunny weather, by daylight, there should be more disturbances because of the Sun activities, but by night signal should be better. That is general rule, of course, but there may be something else in your case. Basically, you have problems under ideal weather conditions, strange. Have you tried to set periodic-calibration=enabled for wireless interfaces? Someone at this forum mentioned this helps under temperature changes.

The only reason you have worse signal by crystal clear nights could be that cloudy nights, actually clouds stop rays from the space and by clear nights there is nothing to stop these disturbances. I have no other idea. Or maybe this has something to do with air moisture.
 
chucka
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Wed Dec 07, 2005 1:14 am

I saw the calibration note, but I have only turned it on on a short test link I have running, so far.

I can only think that maybe I am picking up some interference from far away when conditions are ideal. Unless of course, it *is* temperature related. It doesn't cause much of a problem because it is usually in the wee hours of the morning.
 
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dbostrom
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Wed Dec 07, 2005 6:14 pm

I saw the calibration note, but I have only turned it on on a short test link I have running, so far.

I can only think that maybe I am picking up some interference from far away when conditions are ideal. Unless of course, it *is* temperature related. It doesn't cause much of a problem because it is usually in the wee hours of the morning.
Very calm air can be problematic because of thermal layering. For instance, the same inversion you can see with your eyes thanks to smog can present refractive surfaces that become more dramatic in their effects the lower the incident angle of the impinging signal, ending up with super refraction and complete or near complete reflection of the signal within the inversion layer depending on incident angle and signal frequency. Basically the same deal as optical "mirages". The result can be similar but opposite in desired outcome to what works so well in another context, tropospheric ducting. In this case your signal can get "stuck" bouncing along in a layer of air and if the antenna on the other end is not in the same layer it can end up receiving an attenuated signal or even no signal at all. When the wind blows the effect is reduced or eliminated.
 
chucka
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Wed Dec 07, 2005 8:34 pm

Thanks for that explanation 'dbostrom'. There is definitely a correlation between the calm air and my link signals. I have sat and watched as a link gradually goes from -64 to -88 and then 'blip', it's gone. :-) A few seconds later (usually) it will reappear at -86 or so and slowly it will go back and forth until it returns to its normal signal level. Sometimes for a brief period the link will return to a signal level 10db or so better than it *should* be. This would make sense if some ducting is going on. I didn't realize that temperature inversions could effect 5.8 GHz but I guess it can.
 
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dbostrom
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Ducting

Wed Dec 07, 2005 9:57 pm

Chucka, there are have been some truly phenomenal hops done at microwave frequencies thanks to tropo thermal ducting:

July '94,July '91
Station: N6CA
Location: 33-43-45 N. ... 118-22-30 W.
Band: 2304, 3456, 5760 Mhz.
Distance: 2474.476 Mi. ... 3982.283 Km.

Talk about trapped in a layer!!!

You would need a very wide ack window to get any throughput at those distances, heh! :shock:

This was done via low power beacons continuously maintained on Mauna Loa in Hawaii w/ transmitter output of around 10w fed into some fairly high gain antennas, but the ducting is the real magic. Turns out there's a whole crowd of fanatics who love nothing more than hanging out and waiting for a duct to open. A little more more info here:

http://hiloweb.com/kh6hme/

Veering slightly more on topic... As to avoiding nasty ducting effects, I've got a feeling based on incident angles to inversions/layers that very long hops might be more reliable if there's a fairly radical elevation difference between one end and the other, if you're in an area subject to frequent bouts of ridiculously calm weather. It would sort of figure that increasing the angle of incidence ought to help I suppose. Meanwhile, what exactly is the dependency on operating frequency is beyond my knowledge. We've got a 19k 5.8 link that's quite reliable but one end is at about 370m while the other is at sea level. We'll shortly be opening up another 5.8 link at 36km; this one has similar elevation differences but perhaps the reduced angle of entry to any potential thermal layer will make it unreliable. We very rarely have truly calm weather where this network is located so hopefully we will not find out.

All this stuff is undoubtedly researched down to a fare-thee-well thanks to the long history of telco microwave coms. Makes me feel like digging for it.
 
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ghmorris
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Thu Dec 08, 2005 1:24 pm

[quote="chucka"]Thanks for that explanation 'dbostrom'. There is definitely a correlation between the calm air and my link signals. I have sat and watched as a link gradually goes from -64 to -88 and then 'blip', it's gone. :-) A few seconds later (usually) it will reappear at -86 or so and slowly it will go back and forth until it returns to its normal signal level. Sometimes for a brief period the link will return to a signal level 10db or so better than it *should* be. This would make sense if some ducting is going on. I didn't realize that temperature inversions could effect 5.8 GHz but I guess it can.[/quote]

We see exactly the same problems on our 50km links, but only at certain times of the year. Early summer and late fall are the two big problem times. Hot days and cold nights trigger our issues.

In addition, when ducting occurs, we also get a big increase in background noise from antennas pointed south in the general direction of Toronto. This adds to our problems by degrading a normally very low noise floor. You can't see this with Atheros cards, but the built-in Orthogon spectrum analyser shows it perfectly.

About the only way around this is frequency, polarity and space diversity. Orthogon radios work very well in these conditions, but the price is prohibitive.

We are going to try polarity and frequency diversity by using two MT links in parallel. One on 5.3, one on 5.8, on opposite polarities on a 4' Mwave dish. Then bond both links together.

George
 
ejansson
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Thu Dec 08, 2005 4:31 pm

We have a link that is only about 20km. Spring and fall It drops. We are now on 3ft dishes with 532 and sr5, Giving us over 40db fad margin. The previous radio was a trango atlas and I watched it drop the link with a fad of more then 32db! Our problem stems from a rise in elevation at one end of the link were the terrain changes from flat farm land to forest and bog. I'm guessing the air gets trapped at the bottom of the incline either reflecting or just absorbing the signal. We did the up grades at the end of the season so I won't know for sure if we have licked the problem or not. Our fades lasted hours to several day! Most of the year my signal is 10-15 dbs off of what my calculations say it should be. Talking with some old timers who worked on the microwave connections across western Ontario (lakes rocks, bogs and trees). They reported fades of 50-60 db! The problem is the hilly terrain and the lakes, trap the warm or cold air in the spring and fall and create these pocket of temperature inversions that can play havoc with a link.

I like the Ideal of using 2 MTs at 5.3 and 5.8. Are you going to use a single dual pol antenna or are you going to ad some spatial diversity with 2 different antennas. On a shorter link some one should try using a CM9 and use both antenna ports and dual antennas.
 
altaphon
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Ducting

Wed Dec 14, 2005 11:35 pm

The comments so far match what we have seen (and what I've read in the old telephone microwave literature). Whenever there is a temperature inversion (cold air near the surface, warmer air as you go higher) ducting can happen, and can cause fades of up to -60 dB and boosts of 10 dB as reported. There's an interesting paper on this at http://www.vhfdx.radiocorner.net/docs/G ... 04V2-1.pdf

Polarization diversity doesn't help much, and the paths have to be fairly widely spaced if you're going to have any result with space diversity. Frequency diversity is often the only answer, the Bell System used 4, 6 and 11 GHz simultaneously on some high reliability links.
 
chucka
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Thu Dec 15, 2005 5:56 am

I ran a test a couple of months ago. I added a vertically polarized test link to my towers that make up my 32km horizontally polarized link. The vertical link which was mounted lower down the towers was weaker(mid 70's) and dropped first and was down for several hours before it re-linked. The original horiz. link only went down for a few seconds at a time occasionally during this time period. I just wanted to see if a vertical link might be less prone to the dropouts or would drop out at different times, but it didn't work out for me. If someone has a vertical link and is having problems with dropouts like this they might try horizontal......
 
spok
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Sat Jan 14, 2006 8:02 pm

HI !
Today i finish configuration, link is working on 57 Km !
 
titius
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Nice :)

Sat Jan 14, 2006 8:35 pm

Which speed???
 
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djape
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Wed Jan 18, 2006 4:12 am

So, did you do bandwidth test? Flood ping etc...
What's the result?
I drink like a pirate and smoke like a hippie...
 
marecare
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Tue Jun 20, 2006 12:17 pm

I have a link for 30km between two cities
It works great for a 6 months, and hope it will for longer.
I do not experieance any kind of problem, sometimes i get a ping DUP
but nothing to worry about.
Greetings for Serbia
 
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jp
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Tue Jun 20, 2006 4:25 pm

Here is a 55km link using Alvarion B14 gear. You will see early morning, the link drops in signal quality, then spikes up in abnormally high signal quality. Look at the year graph, and it's most stable in the winter. This signal quality in measured in db signal-to-noise ratio instead of pure -dbm rssi.
One end is at about 600' ASL, the other 350' ASL.

Image
 
spok
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Wed Jun 21, 2006 12:03 am

My expiriance 57 km link @ 5ghz

In summer-time signal verty variable ( from -68 to - 85 dBm)
Aslo signal at day it lower (for -5 to - 10 dBm) that at night.

SRN from 29 to 38 dB...

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