Re: [WISPA] Long 5Ghz link over water
I do have a TLink-45 pair sitting around (non connectorized) that I could test. Is there a hack to put a pigtail on these? 23 miles is pushing the range of the internal antennas. If the enclosure is removed from the antenna, by undoing the 9 screws, it is possible to connect the Tlink to an external antenna in a temporary way. It has the standard internal MCX connectors same as all the other 5830 radios have inside. BUT, the jack are soldered directly to teh Mainboard, and lined up to slide into the plugs hard fastened on the antena, So the depth of the MCX jack is really tight to the side that would be facing the antenna, with only like a millimeter clearance or so. So it is NOT possible to plug in a MCX pigtail to it and still screw to the antenna or put a flat back plate. So only way to keep a pigtail on (external antenna) is if the radio is left open. As well the Radio then would have no way to mount to a pole, as the mounts are on the antennas. BUT, you could leave the Tlink open with the pigtail, and put the whole Tlink inside a larger enclosure. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Jeremy Parr jeremyp...@gmail.com To: WISPA General List wireless@wispa.org Sent: Wednesday, October 28, 2009 10:44 PM Subject: Re: [WISPA] Long 5Ghz link over water 2009/10/28 Tom DeReggi wirelessn...@rapiddsl.net: Its relevent to disclose the radio OS type using. (You stated using a R5H a Mikrotik card, but weren't clear if using Mikrotik OS). The symptom you are explaining sounds similar to how some of my Mikrotik OS units had responsed to noise. Basically they kept dropping speed until they disconnected. It was like watching a clock tick down to zero, and repeat. I had this problem recently with 900Mhz and MIkrotik, and the problem was curred as soon as I switch to a different brand product. I'm suspect, but not verified, nor conclusive, that it could be a Mikrotik driver issue. The point I'm making is that you are likely getting some sort of noise or multi-path (self noise), but the overall problem may not be the noise/multi-path but instead the inabilty of your product to adequately deal with that noise/multipath RF conditions. Yup, it is Mikrotik 4.1 at both ends, on Routerboard 433AH boards, fed by a 24v DC plant (batteries and charger). The easiest place to do a science project probably isn't between two towers seperated by a 20 mile body of water, but it would make for a very interesting and meaningful science project. The link doesn't have traffic over it, the site is currently fed by a T1, so I have some time to play mad scientist without any negative effects to customers. Sure a Mimo card w/ Dual Pol (for single stream) or Space Diversity would likely help deal with Multipath. But what I wonder is whether the same bad results are replicated with other single channel products of similar spec. It would be interesting to put up a Tlink-45, get results of it's noise survey scan, and see if it overcomes the problem. Or even try a StarOS box. Its also relevent to understand how much of the issue is canceled RF, and how much is side effects of 802.11 CDMA? I'm wondering if a TDD system w/ good ARQ better handles it. I do have a TLink-45 pair sitting around (non connectorized) that I could test. Is there a hack to put a pigtail on these? If the power is turned down on the troublesome end, only possible during the times of day when the RX level is decent, the bandwidth test runs faster and longer before it drops to nothing. This might make the link usable, if Mikrotik had some sort of variable transmit power control to maintain 10-20db SNR. My point here is in an ideal world a radio should never have the characteristic to start at 6mb and slowly go to Zero. Instead it should stay at 6mbps, and just have a very high error count. Even if it has 50% packet loss it should stay associated, and with a TDD system w/ARQ it likely would.. When performing the test, the amount of retransmissions push the data rate down from 54 to progressively lower modulation speeds. I am running 5Mhz channels (tried 10, and 20) so this explains the progressive drop to low throughput and ultimate disconnection in my mind. Also note, if Using Mikrotik, they now support Atheros's threshold feature, to mask out weak signals, this can help reduce multipath signal. (although use cutiously as there can be significant fade of water with Fog/Clouds/evaporation/Solar and such.) Obviously if you switched to a TDD MIMO system, you'd optimize your chance for success, but you would not be able to learn what factor most helped the improvement. WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org
Re: [WISPA] Long 5Ghz link over water
2009/10/28 Jeremy Parr jeremyp...@gmail.com: I have a 23 mile link completely over water that I cannot get stable. One end is approx 200ft AGL, 220ft ASL, the other end is 50' AGL, 90' ASL. Antennas are V-Pol 29dbi grids, radios are R5H cards. I have tried the link at both 5.2, and 5.8, but it still fluctuates dramatically. When the antennas were installed and configured for a 5Mhz channel, I was able to aim them to -55, but still they go down during parts of the day. I have a second antenna hung on the 200ft end, at about 185', connected to a second R5H set up for H-Pol which I am going to light up as soon as I get the other end mounted H-Pol. Any other suggestions for getting this stable? I also notice some strangeness when doing bandwidth tests. I can get a steady 8mbps downstream from the 200ft end to the 50' end, but from the 50' end to the 200ft end, the transfer starts at about 6mbps, then slowly drops down to 0, and the client radio (the 50' end) drops. My assumption is multipath reflections off of the water at the lower end, but I cannot be sure. The water is tidal, with as much as a 3' change from low to high, and is connected to the ocean, so there can be considerable chop and wave action on the surface. I just swapped this link to H-Pol, and it needs to be watched overnight, but looks good so far. Signal fluctuating between -59 and -66 on a 20mhz channel, CCQ at 90/90 or better. After flipping to H-Pol, the channel was still set to 5Mhz, and the same fast start and slowdown was occurring, the radio would disassociate with poll timeouts and too many retransmissions. Switching to a 20mhz channel fixed this. status: running duration: 3m59s tx-current: 15.7Mbps tx-10-second-average: 18.0Mbps tx-total-average: 17.4Mbps rx-current: 16.3Mbps rx-10-second-average: 17.2Mbps rx-total-average: 17.2Mbps lost-packets: 60 random-data: no direction: both tx-size: 1500 rx-size: 1500 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/
Re: [WISPA] Long 5Ghz link over water
Your probably seeing tidal dropouts. We have that problem from time to time and usually a larger antenna does the trick with a narrower beam. I would go to 32 dbi dishes at HPOL (I think H-Pol works better over water from experience) I would probably look into use XR-5 cards for the extra output power at 5.8ghz. -Cameron -Original Message- From: wireless-boun...@wispa.org [mailto:wireless-boun...@wispa.org] On Behalf Of Jeremy Parr Sent: Wednesday, October 28, 2009 9:21 AM To: WISPA General List Subject: [WISPA] Long 5Ghz link over water I have a 23 mile link completely over water that I cannot get stable. One end is approx 200ft AGL, 220ft ASL, the other end is 50' AGL, 90' ASL. Antennas are V-Pol 29dbi grids, radios are R5H cards. I have tried the link at both 5.2, and 5.8, but it still fluctuates dramatically. When the antennas were installed and configured for a 5Mhz channel, I was able to aim them to -55, but still they go down during parts of the day. I have a second antenna hung on the 200ft end, at about 185', connected to a second R5H set up for H-Pol which I am going to light up as soon as I get the other end mounted H-Pol. Any other suggestions for getting this stable? I also notice some strangeness when doing bandwidth tests. I can get a steady 8mbps downstream from the 200ft end to the 50' end, but from the 50' end to the 200ft end, the transfer starts at about 6mbps, then slowly drops down to 0, and the client radio (the 50' end) drops. My assumption is multipath reflections off of the water at the lower end, but I cannot be sure. The water is tidal, with as much as a 3' change from low to high, and is connected to the ocean, so there can be considerable chop and wave action on the surface. 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/
Re: [WISPA] Long 5Ghz link over water
From my understanding from others doing that very thing h pol is far better over water then v pol and I would agree that it would work better with the wave going side to side instead of up and down (less chance of bounced reflection on the water surface causing multipath issues). /Eje Sent via BlackBerry from T-Mobile -Original Message- From: Jeremy Parr jeremyp...@gmail.com Date: Wed, 28 Oct 2009 09:20:58 To: WISPA General Listwireless@wispa.org Subject: [WISPA] Long 5Ghz link over water I have a 23 mile link completely over water that I cannot get stable. One end is approx 200ft AGL, 220ft ASL, the other end is 50' AGL, 90' ASL. Antennas are V-Pol 29dbi grids, radios are R5H cards. I have tried the link at both 5.2, and 5.8, but it still fluctuates dramatically. When the antennas were installed and configured for a 5Mhz channel, I was able to aim them to -55, but still they go down during parts of the day. I have a second antenna hung on the 200ft end, at about 185', connected to a second R5H set up for H-Pol which I am going to light up as soon as I get the other end mounted H-Pol. Any other suggestions for getting this stable? I also notice some strangeness when doing bandwidth tests. I can get a steady 8mbps downstream from the 200ft end to the 50' end, but from the 50' end to the 200ft end, the transfer starts at about 6mbps, then slowly drops down to 0, and the client radio (the 50' end) drops. My assumption is multipath reflections off of the water at the lower end, but I cannot be sure. The water is tidal, with as much as a 3' change from low to high, and is connected to the ocean, so there can be considerable chop and wave action on the surface. 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/
Re: [WISPA] Long 5Ghz link over water
Is going to circular polarization an option? Greg On Oct 28, 2009, at 8:50 AM, Jeremy Parr wrote: I have a 23 mile link completely over water that I cannot get stable. One end is approx 200ft AGL, 220ft ASL, the other end is 50' AGL, 90' ASL. Antennas are V-Pol 29dbi grids, radios are R5H cards. I have tried the link at both 5.2, and 5.8, but it still fluctuates dramatically. When the antennas were installed and configured for a 5Mhz channel, I was able to aim them to -55, but still they go down during parts of the day. I have a second antenna hung on the 200ft end, at about 185', connected to a second R5H set up for H-Pol which I am going to light up as soon as I get the other end mounted H-Pol. Any other suggestions for getting this stable? I also notice some strangeness when doing bandwidth tests. I can get a steady 8mbps downstream from the 200ft end to the 50' end, but from the 50' end to the 200ft end, the transfer starts at about 6mbps, then slowly drops down to 0, and the client radio (the 50' end) drops. My assumption is multipath reflections off of the water at the lower end, but I cannot be sure. The water is tidal, with as much as a 3' change from low to high, and is connected to the ocean, so there can be considerable chop and wave action on the surface. graph_image.php.png 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/ 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/
Re: [WISPA] Long 5Ghz link over water
It's probably ducting. Where the conditions in the AIR literally bend the signal over or under your receive antennas. You'll likely have to put in a system designed with something called antenna diversity. Basically two antennas for each link. One 10 to 20' higher than the other one. Then the radio will listen to the two of them and switch to the one with the greater signal levels for it's data flow. I always wanted to try this using a splitter placed EXACTLY in the middle of the two. But with wave lengths so small I don't think it's likely that I'd get it close enough without a lot of blind luck (get it wrong and you create multipath inside the cables). This'll be a tough one. marlon - Original Message - From: Jeremy Parr jeremyp...@gmail.com To: WISPA General List wireless@wispa.org Sent: Wednesday, October 28, 2009 6:20 AM Subject: [WISPA] Long 5Ghz link over water I have a 23 mile link completely over water that I cannot get stable. One end is approx 200ft AGL, 220ft ASL, the other end is 50' AGL, 90' ASL. Antennas are V-Pol 29dbi grids, radios are R5H cards. I have tried the link at both 5.2, and 5.8, but it still fluctuates dramatically. When the antennas were installed and configured for a 5Mhz channel, I was able to aim them to -55, but still they go down during parts of the day. I have a second antenna hung on the 200ft end, at about 185', connected to a second R5H set up for H-Pol which I am going to light up as soon as I get the other end mounted H-Pol. Any other suggestions for getting this stable? I also notice some strangeness when doing bandwidth tests. I can get a steady 8mbps downstream from the 200ft end to the 50' end, but from the 50' end to the 200ft end, the transfer starts at about 6mbps, then slowly drops down to 0, and the client radio (the 50' end) drops. My assumption is multipath reflections off of the water at the lower end, but I cannot be sure. The water is tidal, with as much as a 3' change from low to high, and is connected to the ocean, so there can be considerable chop and wave action on the surface. 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/ 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/
Re: [WISPA] Long 5Ghz link over water
2009/10/28 Marlon K. Schafer o...@odessaoffice.com: It's probably ducting. Where the conditions in the AIR literally bend the signal over or under your receive antennas. You'll likely have to put in a system designed with something called antenna diversity. Basically two antennas for each link. One 10 to 20' higher than the other one. Then the radio will listen to the two of them and switch to the one with the greater signal levels for it's data flow. I always wanted to try this using a splitter placed EXACTLY in the middle of the two. But with wave lengths so small I don't think it's likely that I'd get it close enough without a lot of blind luck (get it wrong and you create multipath inside the cables). Exactly. My thoughts went to an 802.11n card, with two antennas on each end. 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/
Re: [WISPA] Long 5Ghz link over water
Have a look at our Radwin2000 MIMO radio- the diversity option is specifically for these applications. Matt Musial Radwin USA Sent via my BlackBerry -Original Message- From: Jeremy Parr jeremyp...@gmail.com Date: Wed, 28 Oct 2009 09:51:21 To: WISPA General Listwireless@wispa.org Subject: Re: [WISPA] Long 5Ghz link over water 2009/10/28 Marlon K. Schafer o...@odessaoffice.com: It's probably ducting. Where the conditions in the AIR literally bend the signal over or under your receive antennas. You'll likely have to put in a system designed with something called antenna diversity. Basically two antennas for each link. One 10 to 20' higher than the other one. Then the radio will listen to the two of them and switch to the one with the greater signal levels for it's data flow. I always wanted to try this using a splitter placed EXACTLY in the middle of the two. But with wave lengths so small I don't think it's likely that I'd get it close enough without a lot of blind luck (get it wrong and you create multipath inside the cables). Exactly. My thoughts went to an 802.11n card, with two antennas on each end. 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/ 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/
Re: [WISPA] Long 5Ghz link over water
Hmmm, hadn't thought of that solution. Good catch! I try to keep my links to 15 miles or less so that I can have an AP at each one and cover the area in between. That helps with a lot of strange performance issues too. Thanks for the tip, I might have to try some n radios after all :-). It's funny how relatively open rules have so rapidly and completely changed everything in our industry. 10 years ago when I started a link with antenna diversity would cost nothing less than $50 or $100k. Usually a lot more. Just to get 10 to 20 megs. Half a million for 100meg. Now we can do it for a few hundred bucks per end. the quality isn't as good with today's gear, but for the cost we can put in 5 of them and have 100% up time instead of a mear 5 nines. marlon - Original Message - From: Jeremy Parr jeremyp...@gmail.com To: WISPA General List wireless@wispa.org Sent: Wednesday, October 28, 2009 6:51 AM Subject: Re: [WISPA] Long 5Ghz link over water 2009/10/28 Marlon K. Schafer o...@odessaoffice.com: It's probably ducting. Where the conditions in the AIR literally bend the signal over or under your receive antennas. You'll likely have to put in a system designed with something called antenna diversity. Basically two antennas for each link. One 10 to 20' higher than the other one. Then the radio will listen to the two of them and switch to the one with the greater signal levels for it's data flow. I always wanted to try this using a splitter placed EXACTLY in the middle of the two. But with wave lengths so small I don't think it's likely that I'd get it close enough without a lot of blind luck (get it wrong and you create multipath inside the cables). Exactly. My thoughts went to an 802.11n card, with two antennas on each end. 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/ 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/
Re: [WISPA] Long 5Ghz link over water
I will have to second the ducting analysis. 23 miles is a long way over a water path. You can use space diversity by using a pair of antennas/radios at the same frequency, with 20 foot or more of vertical separation. You could try frequency diversity also. Many times a duct will affect frequencies differently at times during the event. You do know grids don't have a very clean pattern. A dish will focus more of the energy where you want it. If you are limited to space on the tower(s), a dual band feed dish might be your solution. You could run 2.4 and 5.8 at the same time and have software vote for the best link at any moment. In the past I built a 20 mile water path with space diversity using very expensive Nortel radios. This was in SW Fl, where ducting is common. The system would switch antennas several times in a month. These were OC3 radios at lower 6 GHz. The upper dishes were 10' and the lower were 6'. I think the separation was 20'. BTW, that was in 1999, and the link is still running. Mike At 08:20 AM 10/28/2009, you wrote: I have a 23 mile link completely over water that I cannot get stable. One end is approx 200ft AGL, 220ft ASL, the other end is 50' AGL, 90' ASL. Antennas are V-Pol 29dbi grids, radios are R5H cards. I have tried the link at both 5.2, and 5.8, but it still fluctuates dramatically. When the antennas were installed and configured for a 5Mhz channel, I was able to aim them to -55, but still they go down during parts of the day. I have a second antenna hung on the 200ft end, at about 185', connected to a second R5H set up for H-Pol which I am going to light up as soon as I get the other end mounted H-Pol. Any other suggestions for getting this stable? I also notice some strangeness when doing bandwidth tests. I can get a steady 8mbps downstream from the 200ft end to the 50' end, but from the 50' end to the 200ft end, the transfer starts at about 6mbps, then slowly drops down to 0, and the client radio (the 50' end) drops. My assumption is multipath reflections off of the water at the lower end, but I cannot be sure. The water is tidal, with as much as a 3' change from low to high, and is connected to the ocean, so there can be considerable chop and wave action on the surface. Content-Type: image/png; name=graph_image.php.png Content-Disposition: attachment; filename=graph_image.php.png X-Attachment-Id: f_g1c41wi50 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/ 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/
Re: [WISPA] Long 5Ghz link over water
Its relevent to disclose the radio OS type using. (You stated using a R5H a Mikrotik card, but weren't clear if using Mikrotik OS). The symptom you are explaining sounds similar to how some of my Mikrotik OS units had responsed to noise. Basically they kept dropping speed until they disconnected. It was like watching a clock tick down to zero, and repeat. I had this problem recently with 900Mhz and MIkrotik, and the problem was curred as soon as I switch to a different brand product. I'm suspect, but not verified, nor conclusive, that it could be a Mikrotik driver issue. The point I'm making is that you are likely getting some sort of noise or multi-path (self noise), but the overall problem may not be the noise/multi-path but instead the inabilty of your product to adequately deal with that noise/multipath RF conditions. The easiest place to do a science project probably isn't between two towers seperated by a 20 mile body of water, but it would make for a very interesting and meaningful science project. Sure a Mimo card w/ Dual Pol (for single stream) or Space Diversity would likely help deal with Multipath. But what I wonder is whether the same bad results are replicated with other single channel products of similar spec. It would be interesting to put up a Tlink-45, get results of it's noise survey scan, and see if it overcomes the problem. Or even try a StarOS box. Its also relevent to understand how much of the issue is canceled RF, and how much is side effects of 802.11 CDMA? I'm wondering if a TDD system w/ good ARQ better handles it. My point here is in an ideal world a radio should never have the characteristic to start at 6mb and slowly go to Zero. Instead it should stay at 6mbps, and just have a very high error count. Even if it has 50% packet loss it should stay associated, and with a TDD system w/ARQ it likely would.. Also note, if Using Mikrotik, they now support Atheros's threshold feature, to mask out weak signals, this can help reduce multipath signal. (although use cutiously as there can be significant fade of water with Fog/Clouds/evaporation/Solar and such.) Obviously if you switched to a TDD MIMO system, you'd optimize your chance for success, but you would not be able to learn what factor most helped the improvement. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Jeremy Parr jeremyp...@gmail.com To: WISPA General List wireless@wispa.org Sent: Wednesday, October 28, 2009 9:20 AM Subject: [WISPA] Long 5Ghz link over water I have a 23 mile link completely over water that I cannot get stable. One end is approx 200ft AGL, 220ft ASL, the other end is 50' AGL, 90' ASL. Antennas are V-Pol 29dbi grids, radios are R5H cards. I have tried the link at both 5.2, and 5.8, but it still fluctuates dramatically. When the antennas were installed and configured for a 5Mhz channel, I was able to aim them to -55, but still they go down during parts of the day. I have a second antenna hung on the 200ft end, at about 185', connected to a second R5H set up for H-Pol which I am going to light up as soon as I get the other end mounted H-Pol. Any other suggestions for getting this stable? I also notice some strangeness when doing bandwidth tests. I can get a steady 8mbps downstream from the 200ft end to the 50' end, but from the 50' end to the 200ft end, the transfer starts at about 6mbps, then slowly drops down to 0, and the client radio (the 50' end) drops. My assumption is multipath reflections off of the water at the lower end, but I cannot be sure. The water is tidal, with as much as a 3' change from low to high, and is connected to the ocean, so there can be considerable chop and wave action on the surface. 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! 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/
Re: [WISPA] Long 5Ghz link over water
2009/10/28 Tom DeReggi wirelessn...@rapiddsl.net: Its relevent to disclose the radio OS type using. (You stated using a R5H a Mikrotik card, but weren't clear if using Mikrotik OS). The symptom you are explaining sounds similar to how some of my Mikrotik OS units had responsed to noise. Basically they kept dropping speed until they disconnected. It was like watching a clock tick down to zero, and repeat. I had this problem recently with 900Mhz and MIkrotik, and the problem was curred as soon as I switch to a different brand product. I'm suspect, but not verified, nor conclusive, that it could be a Mikrotik driver issue. The point I'm making is that you are likely getting some sort of noise or multi-path (self noise), but the overall problem may not be the noise/multi-path but instead the inabilty of your product to adequately deal with that noise/multipath RF conditions. Yup, it is Mikrotik 4.1 at both ends, on Routerboard 433AH boards, fed by a 24v DC plant (batteries and charger). The easiest place to do a science project probably isn't between two towers seperated by a 20 mile body of water, but it would make for a very interesting and meaningful science project. The link doesn't have traffic over it, the site is currently fed by a T1, so I have some time to play mad scientist without any negative effects to customers. Sure a Mimo card w/ Dual Pol (for single stream) or Space Diversity would likely help deal with Multipath. But what I wonder is whether the same bad results are replicated with other single channel products of similar spec. It would be interesting to put up a Tlink-45, get results of it's noise survey scan, and see if it overcomes the problem. Or even try a StarOS box. Its also relevent to understand how much of the issue is canceled RF, and how much is side effects of 802.11 CDMA? I'm wondering if a TDD system w/ good ARQ better handles it. I do have a TLink-45 pair sitting around (non connectorized) that I could test. Is there a hack to put a pigtail on these? If the power is turned down on the troublesome end, only possible during the times of day when the RX level is decent, the bandwidth test runs faster and longer before it drops to nothing. This might make the link usable, if Mikrotik had some sort of variable transmit power control to maintain 10-20db SNR. My point here is in an ideal world a radio should never have the characteristic to start at 6mb and slowly go to Zero. Instead it should stay at 6mbps, and just have a very high error count. Even if it has 50% packet loss it should stay associated, and with a TDD system w/ARQ it likely would.. When performing the test, the amount of retransmissions push the data rate down from 54 to progressively lower modulation speeds. I am running 5Mhz channels (tried 10, and 20) so this explains the progressive drop to low throughput and ultimate disconnection in my mind. Also note, if Using Mikrotik, they now support Atheros's threshold feature, to mask out weak signals, this can help reduce multipath signal. (although use cutiously as there can be significant fade of water with Fog/Clouds/evaporation/Solar and such.) Obviously if you switched to a TDD MIMO system, you'd optimize your chance for success, but you would not be able to learn what factor most helped the improvement. 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/
