Thanks Tom. You are correct, we are using the integrated panels for antennae. I will dig into this over the weekend and/or early next week.
Tom DeReggi wrote: > Scott, > > You are doing the right thing targetting a -60 rssi. We design most of our > TLINKs to operate there, because they can distort after -58 and maximum RSSI > is beneficial for top modulation. > > I see two relevent topics to address. > 1) Why its dropping on one end, and > 2) How well does Adaptive modulation work. > > WE ALWAYS LEAVE ADAPTIVE MODULATION OFF AND HARD SET BEST MODULATION for > Tlinks. > My personal feeling is that Tlink's adaptive modulation does not work well. > We have found that it will stay on channels that are bad for to long. > For example, if 54mod had 80% loss, and 36mod had 20% loss, and 24mod had > zero loss, its not uncommon for the link to set it self to 36 mod and > operate as a compromised link. > We found that reducing packet loss is more important for TCP Throughout, > that LAyer2 speed. Trango considers layer2 for picking best modulation and > does not consider effect to TCP congestion control algorithyms. We just dont > trust the Adaptive Modulation. Dont misunderstand me, we LOVE TLink-45s, > they are our favorite radio under 30mbps, and work great when we hard set > modulation. We rely on Linktest to establish what modulation is best to set > each radio on. Meaning which modulation has least packet loss. As you know, > each side can work at a different modulation. So it can take some playing to > find the best modulation for each side. > > Sure it is possible that you have a bad radio on one end, and if you cant > solve, would be worth swapping the radio. But I'd consider that as a last > resort. > > Its very common to have noise floors that are different on one side of a > link than the other. And it can be very common to have noise over a large > number of channels. > Remember Wifi channelsare 10Mhzspace off that of Trango, and some full > duplex radio space their channels far apart. So one competitor's radio can > sometimes chew up a lot of free channels. > Have you tried both polarities? Or just channels. > > You have a perfect case for showing the high value of Trango. They give you > the tool to solve this. You need to rely on Trango's embedded Spectrum > scanning feature. You need to know the noise floor on BOTH sides to progress > in troubleshooting this. > > On each side, run the spectrum scan on every channel, and copy to note pad, > and compare noise floor picked up. Peak noise is most relevent.. > > Remember it takes 30db of SNR to reliably work at 54mb. And about 20-25db to > operate at 36mb. But it only takes about 12db SNR to operate at 12mbps. > > Lastly, you should not judge whether your hardware is working well by what > modulation is detected. Instead rely on Linktest to view packet loss at each > modulation. That will give you clues. > For example, if you have a bad radio, maybe its likely you might get packet > loss on all your modulations of similar percentages. > > If packet loss drops proportionally to modulation (ex, 54mb 90%, 48 80%, > 36mb 60%, 24mb 40%), you can be certain packet loss is proportional to the > SNR, and therefore most likely truely a noise source interfering with you. > > If the RU is the one going to tx at 12mb, at a first glance it would be > probable that the noise is at the MU side. But do not rely on that > assumption. We have found otherwise many times. > > I'm assuming you are using integrated panels at 2 miles. If not, and using > pigtails, make sure both side have the pigtails going to the correct > polarities. We've had cases where tech's made a mistake and reverse the > radio pigtail on one side, but because the radio is so close, and > autoTXpower was on, it still worked and had similar RSSI on each end. So it > was important to verify that TX power is hard set to the same value on BOTH > sides. We decoverd our mistake, simply by swapping the polarity just on the > near radio, and watching the packet loss go away, then verified with site > visit. > But if TX powers hard set equally, and equal RSSI, polarity is probably > correct. > > Also remember that alignment is not symetrical to the other side. Or I > should say Multi-path is not always symetrical. In theory, a reflective path > is symetical if each side's Transmitted signal hits the same shape object > that reflects the signal. But in many environments in the real world that > are not the condition of reflective opject. For example an object shaped > like 1\ . If getting multi-path on one side, its feasible that the RSSI > could still be equal. Again, this is not a likely the cause, when you have a > short LOS link, and can see everything in the path. But I can give you one > example, where we had a panel mount loosen, and the panel fell pointed down > to the roof, but because close and autopowerleveing, the link stayed up, but > the link was established through multi-path. We showed up with a > replacement radio after remote diag, and learned all we needed to do is > realign. > > One of the ways to partially test alignment remotely is to match RSSI with > LinkBudget. Again, autopowerlevels, can mislead you, so turn it off. > Manually reduce the power level, until you get the desired rssi, then use > Trango's BUdget Calculator and confirm it matches the results. If calcs > match, its most likely aligned good enough. > > So in summary, it probably is noise. Hardset config, no auto anything. Rely > on Survey and Linktest commands to Diagnose. > > I'm not saying its not OK to use Auto on an ongoing basis. Just definately > disable it during the troubleshooting process, so you have controlled > factors to compare. > . > Tom DeReggi > RapidDSL & Wireless, Inc > IntAirNet- Fixed Wireless Broadband > > > ----- Original Message ----- > From: "Scott Reed" <scottr...@onlyinternet.net> > To: "WISPA General List" <wireless@wispa.org> > Sent: Friday, January 08, 2010 9:14 AM > Subject: [WISPA] TrangoLink45 Link Problem > > > >> I have a 2 mile link with TrangoLink45's. Clear line of sight. >> The MU transmits at 54Mbps all the time. >> The RU drops to 12Mbps within about 2 minutes of setting it to 54. >> This morning we tried 6 or 7 different channels. All had the same RSSI >> of -61 or -62. All behaved the same way. >> What else should I be looking for to keep the RU sending at 54? Of >> course the customer receive side is the one that is slow and this link >> services about 60% of the customers. >> >> -- >> Scott Reed >> Sr. Systems Engineer >> GAB Midwest >> 1-800-363-1544 x4000 >> Cell: 260-273-7239 >> >> >> >> -------------------------------------------------------------------------------- >> WISPA Wants You! Join today! >> http://signup.wispa.org/ >> -------------------------------------------------------------------------------- >> >> WISPA Wireless List: wireless@wispa.org >> >> Subscribe/Unsubscribe: >> http://lists.wispa.org/mailman/listinfo/wireless >> >> Archives: http://lists.wispa.org/pipermail/wireless/ >> >> >> -- >> Internal Virus Database is out-of-date. >> Checked by AVG. >> Version: 7.5.560 / Virus Database: 270.12.26/2116 - Release Date: >> 5/15/2009 6:16 AM >> >> >> > > > > -------------------------------------------------------------------------------- > WISPA Wants You! 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