lutful
Premium
join:2005-06-16
Ottawa, ON
 ·TekSavvy Solutions..
| Low-cost 900Mhz NLOS feasibility test
Many customers do dream of making 900Mhz links through miles of forests.
The following equipment provide a very low-cost "NLOS feasibility" test setup:
Pair of 900Mhz directional antennas such as Poynting.
Pair of 900Mhz "wireless serial modem" radios such as Maxstream 9Xtend [ RX -106dBm TX: 0-30dBm adjustable ]
By manipulating the radio's TX output, "potential" Canopy/Trango link margins can be "simulated" to see if there is a "snowball's chanmce in hell" of a real link working somewhere 
The RX sensitivity and diagnostic features also tell what the 900Mhz environment is like at a particular location |
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dbostrom
join:2005-11-03
Atlanta, GA
1 edit | Those Maxstream radios are -extremely- virtuous. Fantasically sensitive; during testing the guys who developed 'em established a useful 30 mile link using 1/4 wave groundplane antennas (admittedly from one end of the Great Valley to the other w/no obstructions). Unless something's changed since I used 'em they're hoppers, which might affect the simulation a bit. Also IIRC they run at 9600bps which is also a bit slow compared with what we're used to.
Another approach might be to use a pair of the RFLinx amplified converters 2.4-->900 as seen here. These allow OTS WiFi gear to be run at 900mhz which would result in a somewhat more familiar. I've not tried these out but on the other hand everything from RFLinx we --have-- tried has worked very well. |
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coldnorth2
join:2005-11-05
Fort Mcmurray, AB
| said by dbostrom  :Another approach might be to use a pair of the RFLinx amplified converters 2.4-->900 Wow! Am I understanding right that you could take a USB WiFi dongle and make it into a 900Mhz CPE ? |
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cmaenginsb
Premium,MVM
join:2001-03-19
Palmdale, CA | reply to lutful
Yes you could if you had access to the antenna connection to connect it to the converter. Then you will need power to power the converter and a 900 Mhz antenna.
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CCNA, Comtrain Certified Tower Climber |
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coldnorth2
join:2005-11-05
Fort Mcmurray, AB
| said by cmaenginsb :Yes you could if you had access to the antenna connection This is too exciting - just did that since my posting! I like equipment "reverse engineering"
Will this really work for a simple 900Mhz AP/Client solution? I wanted to use WPA certificate security which these dongles + WinXP provide. |
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public
join:2002-01-19
Santa Clara, CA
·DSL EXTREME
| reply to lutful
said by lutful :Many customers do dream of making 900Mhz links through miles of forests. There are $600 kits of two ptp ethernet bridge radios at 1.5Mbps at 900 MHz.
Maxstream is one but there is couple of others. |
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dbostrom
join:2005-11-03
Atlanta, GA
| reply to coldnorth2
said by coldnorth2 :said by cmaenginsb :Will this really work for a simple 900Mhz AP/Client solution? I wanted to use WPA certificate security which these dongles + WinXP provide. W/the RFLinx converters, everything that can happen at 2.4ghz will happen at 900mhz. That is, with the exception that due to design considerations the converters work from/to wifi channel 7 only, which of course is not a factor on the wifi side of things as the original 2.4 signal never appears in 2.4 spectrum. Regarding the other post about Maxstream 1.5mbps gear, that sounds pretty exciting. I only had the opportunity to work w/Maxstream during their infancy, on a telemetry project, and their little 900meg 9.6kbps hoppers we were using were stunningly well engineered. We ended up buying over a thousand of 'em. |
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wispman
join:2004-12-21
USA
| reply to lutful
There are distributors out there who will let you "try it before you buy it"
Now that Trango got rid of all their distributors and are doing it all factory direct, you might check with them. I would bet they might venture into this to get sales. |
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
1 edit | reply to lutful
said by lutful :By manipulating the radio's TX output, "potential" Canopy/Trango link margins can be "simulated" to see if there is a "snowball's chanmce in hell" of a real link working somewhere Radio Mobile will do that job better. These low speed, narrow band (hoppers are relatively narrowbanded), systems can not be used to accurately model the performance of a DSSS system in the real world.
Canopy is a DSSS TDM system which is a much higher data rate system, with a much lower SNR requirement.
In short, you can't get there from here.
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How can I improve my WiFi signal? |
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lutful
Premium
join:2005-06-16
Ottawa, ON
·TekSavvy Solutions..
| said by DaDogs :Canopy is a DSSS TDM system which is a much higher data rate system, with a much lower SNR requirement. ... In short, you can't get there from here. I want to immediately move to this alternate universe where much higher data rate requires much lower SNR
May I rephrase my practical suggestion so that the simple logic becomes clear ...
IF, using same 900Mhz antennas on same towers,
a maxstream radio pair with Tx power of 1 watt and RX sensitivity in the "femtowatt" range set to the lowest data rate of 9600baud cannot make a link ...
THEN
there is "snowball's chance in hell" of making said link with expensive 900Mhz "brandname" radios - even if the radios are provided free for testing ...
Same logic will hold true (in our universe) for all RF frequencies but I am still looking for a 5Ghz "test radio" for customers dreaming of "Orthogonal and Proximity" miracles  |
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
| said by lutful : said by DaDogs :Canopy is a DSSS TDM system which is a much higher data rate system, with a much lower SNR requirement. ... In short, you can't get there from here. I want to immediately move to this alternate universe where much higher data rate requires much lower SNR Me too!!! I should have made myself more clear. I'm saying that those narrowband systems (which are great little systems) have such high receiver thresholds and place so much power (relatively) in such a narrow sliver of the spectrum, they are not a good simulation of a DSSS system.
said by lutful :May I rephrase my practical suggestion so that the simple logic becomes clear ... IF, using same 900Mhz antennas on same towers, a maxstream radio pair with Tx power of 1 watt and RX sensitivity in the "femtowatt" range set to the lowest data rate of 9600baud cannot make a link ... THEN there is "a snowball's chance in hell" of making said link with expensive 900Mhz "brandname" radios - even if the radios are provided free for testing ... Aye. I see the point.
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How can I improve my WiFi signal? |
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wispman
join:2004-12-21
USA | It only takes a few inches to make some of my 900 links go down. You really just have to buy the gear and try it. It's just too fussy. |
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lutful
Premium
join:2005-06-16
Ottawa, ON
·TekSavvy Solutions..
| said by wispman :takes a few inches to make some of my 900 links go down. That's what is so frustrating ... 
said by wispman :You really just have to buy the gear and try it. Many folks do that but RMA from Canada is a pain  |
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA | reply to wispman
Ayup at 900 MHz three inchs is the difference between in phase and 180 degrees out of phase with nearby reflectors.
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How can I improve my WiFi signal? |
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lutful
Premium
join:2005-06-16
Ottawa, ON
·TekSavvy Solutions..
| said by DaDogs :three inchs is the difference between in phase and 180 degrees out of phase DaDogs, do you know if any commercial 900Mhz units use "diversity" or "MIMO" to account for this? |
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
| said by lutful :said by DaDogs :three inchs is the difference between in phase and 180 degrees out of phase DaDogs, do you know if any commercial 900Mhz units use "diversity" or "MIMO" to account for this? I don't know of any but I have not surveyed the offerings that throughly.
Canopy has one antenna input. I'd suspect that 802.11b down converters could be used with a standard WiFi unit that does diversity.
Might be interesting.
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How can I improve my WiFi signal? |
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