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nowoxi
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faustrating issues on performance

Sun Feb 26, 2006 2:23 am

i have an mt525 board and a 1 watt pcb amp. i have being using this kinda amp for a while but they kept on packing up after 3 weeks. the last 1 i was given "cos of my devotion" i guess has being on for a while now more than 3 weeks but the problem am having with that now is that the performance is alot worse than it used to be alot worse.

its like the sensitivity of the radio increased but at the client point sit reduced. i connected a clietn which was reading -83 at the client end and -79db on MT and that was at the same time. i wonder why there would be such disparity in performance. 1 thing i can remember is that when i was about to return the MTbox up on the mast a blind folk hit the table and the box dropped. i cross checked everything to see if that was the problem but i could still find nothing. yeah i also installed the box in a box with a hole at the bottom and i added a heat sink to the base of the pcb amp. please i would like someone to help me with this. why is it that i cant have a third of my coverage. i have spent so much. what could be wrong is it the borard the wlan card pigtales amp antenna or the wholethig or just joints. please i need help
 
cibernet
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Re: faustrating issues on performance

Sun Feb 26, 2006 4:47 am

i have an mt525 board and a 1 watt pcb amp. i have being using this kinda amp for a while but they kept on packing up after 3 weeks. the last 1 i was given "cos of my devotion" i guess has being on for a while now more than 3 weeks but the problem am having with that now is that the performance is alot worse than it used to be alot worse.

its like the sensitivity of the radio increased but at the client point sit reduced. i connected a clietn which was reading -83 at the client end and -79db on MT and that was at the same time. i wonder why there would be such disparity in performance. 1 thing i can remember is that when i was about to return the MTbox up on the mast a blind folk hit the table and the box dropped. i cross checked everything to see if that was the problem but i could still find nothing. yeah i also installed the box in a box with a hole at the bottom and i added a heat sink to the base of the pcb amp. please i would like someone to help me with this. why is it that i cant have a third of my coverage. i have spent so much. what could be wrong is it the borard the wlan card pigtales amp antenna or the wholethig or just joints. please i need help
An advise... dont use amps...


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nowoxi
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Sun Feb 26, 2006 5:16 am

YEAH I KNOW BUT I DONT GET VERY FAR WITHOUT THEM
 
cibernet
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Sun Feb 26, 2006 5:28 am

YEAH I KNOW BUT I DONT GET VERY FAR WITHOUT THEM
Don´t use capital letters.... Try ubiquiti SR2 400mW...

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José Ignacio Acosta
Cibernet Comunicaciones / Mikronet
Joaquín V. González
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Beccara
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Sun Feb 26, 2006 5:36 am

YEAH I KNOW BUT I DONT GET VERY FAR WITHOUT THEM
First of all dont uses CAPS, its just likly to get you ignored.

2nd of all, Dont use amps, they simpley suck - if you cant get the link without them then there are issues with your link budget and its not going to be a 40mbit link.

You cant ignore the laws of physics Jim
 
theoryman
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Sun Feb 26, 2006 6:30 am

Sorry to disagree, but, amps can work just fine if you use high quality units and engineer your system properly.

I have 27 outdoor amps in service, a mixture of Hyperlink and RF Linx units. My network has been in operation for 7 years and the amps are far less troublesome than the other electronics in the network. I have had 2 amps fail in 7 years, both after direct lighting strikes.

I use amps in locations where the advantage of having the radio and controller easily accessible outweigh the additional cost of the amp. Especially in locations difficult to climb in bad weather.

On the other hand, the pcb amps, in my experience, are a waste of time and money. If your going to put the radio up close to the antenna anyway, why not use a high power card?

--
Blair Davis
West Michigan Wireless ISP
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nowoxi
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Sun Feb 26, 2006 10:41 am

sorry about the caps. i guess i just put it there cos i mistakenly turned on the caplock button. no other reason

so u suggest i just get an opgrade on the card in stead all other stuff. then what do u think about a hyperlink amp
 
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Sun Feb 26, 2006 11:34 am

amps have been on my mind recently. I read these forums often, and I see it mentioned over and over again: Don't use amps.

You see, I do use amps. 1 watt bi-di hyperlink at all my locations. When I first got into wireless, I found that it helped me get installs done fast. I live in a 5 mile wide X 10 mile long valley. When I started, almost no one had wireless up, and service was excellent.

Well, now that's a different story, and I find that long-time customers are having problems with consistant service. My ping times are all over the map. So, I am left scratching my head. I went wardriving in our little town (15,000 pop) and found over 200 APs, mostly QWEST ACTIONTEC routers. So I am wondering if my amps are now picking up noise, thus causing poor performance.

I took the amp of my omni today. It's located downtown. Much to my surprise, with the latest firm (2.9.14) I am still reaching all my clients. Strength is down, but pings are consistant! I am going to slowly attempt to phase out amps, and see if QOS improves. Perhaps you should do the same?
 
nowoxi
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Sun Feb 26, 2006 12:08 pm

so how many basestations do you have
 
YappaDappa
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Sun Feb 26, 2006 12:13 pm

I have 6. all about 3 miles apart (two are on a ridge, and can see neighboring villages)

I guess my point is, if you are in a low traffic area, and need great distances, AMPS work fine. I am about to determine if our newly crowded RF environment is what is causing problems in the main part of town. I think I will still keep the amps on the sector antennas shooting away from the city
 
nowoxi
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Sun Feb 26, 2006 12:25 pm

bt i dont know what is causing my own problem remmebr i said the quality has dropped. i use a pcb amp. it used to cover a 1kmsq area for centirnos and atleast what i tested 3kmsq radius for out door equipment. i practically had nlos clients connect from indoor but now its all different after the last installation
 
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Sun Feb 26, 2006 6:11 pm

amps can help on ptp links for sure if you also use high gain antennas !!
but on AP / ptmp installations they are useless - only produce problems
we tried it out a few years ago .....

if you use good wireless hardware on both ends (antennas, cabels and cards) then everyting works trouble free !
 
nowoxi
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Sun Feb 26, 2006 8:40 pm

hey ok so what do you have there or what would work for a range like mine.u can make any assumptions u want
 
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dbostrom
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Sun Feb 26, 2006 8:42 pm

Sorry to disagree, but, amps can work just fine if you use high quality units and engineer your system properly.
Agreed. If you use an SR5 or SR2, you're using an amplifier.

Some years ago, in another life, I did engineering for AM and FM radio stations. Typically we'd use a device called an "exciter" to create a signal large enough, say 10w, to drive maybe a 250w intermediate power stage, this driving perhaps a 10kw final output amplifier. Bear in mind, the exciter had at least two amplification stages inside it. The noise figures out of the end of this long chain of amplifiers was excellent.

It's foolish to say "amplifiers are bad" without exception.

Antennas are a inexpensive, elegant and often effective way of improving the performance of an RF system. That being said, amplifiers are part of life in RF systems and to entirely eschew them is to ignore the reality of asymmetric systems such as PTMP where high gain endpoints are talking to omni directional distribution nodes, such as FM broadcast and data networks.
 
avantwireless
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Mon Feb 27, 2006 3:47 am

One little secret about rflinx amps ( and all without exterior boxes). Make sure the components of the amp are facing away from your AP circuit boards. Have the metal heat sink between the two devices. Muchly reduces crosstalk across components...

Robert
 
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sten
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Tue Feb 28, 2006 12:42 am

hey ok so what do you have there or what would work for a range like mine.u can make any assumptions u want
why is 1 square km with ap and centrino difficult? Other than the timing on the centrino cards is limited to roughly 500 meters and will create enormous amounts of retransmissions and extremely low speeds with just a single client connected).

How about using one type of antenna that receives real well and one that sends real well? Or even better, use multiple access points and rid yourself of multiple severe problems. One of your problems might be that centrino's lower their output power real quick depending on the signal they perceive. So if you send strong they (at least in some drivers/versions) will assume you are very close to the access point and lower transmit power level.

But i guess you considered these things when you bought that amplifier.
Move along. Nothing to see here.
 
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djape
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Tue Feb 28, 2006 11:33 am

I'm repeating like parrot :D
Don't use amps, they are just giving you higher signals but bigger noise also.
Amps are not cheap, so spend that money on more AP's, if you need more coverage, do mesh network....
I drink like a pirate and smoke like a hippie...
 
nowoxi
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Tue Feb 28, 2006 6:55 pm

so what do you do when you are not allowed to but reapeters in some areas were they ought to be. like am not allowed to install aps at those points. i guess i still have to turn to amps. or what do u think?
 
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Wed Mar 01, 2006 12:55 am

if we think of amps, we think of:

http://www.ssb.de/englisch/products/lan/lan-amp_e.html

and we use them. Putting a 1Watt amp on a 10km link (not really line of sight) with a 14dbi antenna, brought the link to -70, 11mbit. Without there was a link with about -91 to -93 about 1mbit.

a very good tip from cmit ;-)
 
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Use of Amps

Thu Mar 02, 2006 2:55 am

Just my two cents and seven years of working with complex ISM networks. You can use amps, you simply need to make sure you design the link properly. Let me explain wihtout getting to technical: Amps come with both a TX and RX gain. The TX or transmit is needed to reach out to your clients. This is where you need the higer power (stay within FCC limits) to ensure you are reaching the client base you need since in order to get the needed coverage area with the lower gain antenna (wider beamwith therefore reducing antenna gain). The problem is in the RX or recieve gain the amplifier has. The basic concept here is you can only amplify a signal that is strong enough to reach the antenna in the first place. RX gain within the amplifier is there to "make up" for the cable loss between the transmitter and the antenna not to "amplify" the singal. If there is no signal or a poor signal at the antenna no amplifier is going to make that signal better, only worse since it amplifies the noise floor as well. The perfect amplifier design is placing the amp at the antenna (or as close as you can) and calibrate the amp for the RX gain to be slightly higer than the cable loss you are going to recieve in the installation. This will effectivly elliminate the cable loss (connectors, arrestors etc) between the transmitter and the antenna. This virtually places your transmitter right at the antenna itself giving you the higest possible "quality" signal it can recieve. The problem with PCB amps is the placement. They are typically placed at the transmitter itself with both a TX and RX gain. This may work for some time, untill there is something placed on or near the band you are working on. This causes sideband or near interfearance (possibly even direct) into your wireless medium (cable, transmitter etc) when this signal hits the PCB amp it increases the strength of the interferance. In some cases this can be ligitimate 802.11 based packets that the hardware will not interperate as noise, the hardware or software simply disregards the packets however this is still overhead to the medium. This increases how hard the equipement has to work therefore reducing your throuput and performance.

I hope this makes sense. I would suggest you try a pole mounted amp placed at the antenna and DC inject, make sure you use the lowest RX rate possible for your installation. In many cases I have ordered custom amps from http://www.rflinx.com to my exact specifications to elliminate this problem.

Hope this helps
 
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normis
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Thu Mar 02, 2006 11:31 am

use amps only if the link quality is very high and there is no noise. because amps will amplify noise also, and the situation will get worse. there are better ways to make good links.

how? ask people who have serious links:
http://forum.mikrotik.com//viewtopic.ph ... ght=#19765
 
nowoxi
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Sat Mar 11, 2006 1:21 am

wel am about to try out everything i v learnt from this site tomorrow so i should let you in on what i think 2morrow
 
nowoxi
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Sun Mar 12, 2006 2:45 am

well guess what i think i fixed the problem. it was the transmit side of the pcb amplifier that was faulty. i changed it to a 1w hyperlink. well the link seems to be back to normal except that i couldnt test with long range clients. but clients could connect like be4

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