I'm looking to connect three farm houses using Buffalo .11g gear (using WDS) to share data and share a cable internet connection. The distances of the paths are 1.25 miles each. I have LOS for the paths. I plan to use relatively short (
Calculation Results
Free Space Loss dB Rx Signal Level dBm Theoretical System Operating Margin dB
1st house to middle house Based on your figures at 1.25 miles, 15 foot each LMR 400, 2 Lightening Arrestors then a 15dbi directional perhaps a yagi with 30 degree beam and an omni with 9dbi would give you an SOM (system operating margin) of 19.4db based on a -87dbm receive sensitivty and a -67.5dbm receive signal. An SOM of at least 10 is required for a stable link. The setup would be the same from the 3rd house back to the middle. You could proably do a 7dbi omni and still get a good link but its up to you. This is with clear RF LOS. If the irrigation system gets in front of the antenna or in the fresnal zone then it could cause some signal degradation.This place has some pretty good prices
dbm
Hmmm. I charge 15% to consult to consultants. ;)
You may find the calculator at this site useful:
No.
Do you mean the same dBi? No.
Not if you plan on using clients locally. Besides, for the distances you are dealing with, a good omni (16 dBi or more) with a bit of downtilt is fine. Keep in mind that there is a "cone of silence" under the antenna when placing it.
Doesn't matter where the antennas are, you need a good Nema ground. Put the grounding block as close to the antenna as possible and run solid core ground wire to the house panel ground point. Using a separate ground point in the ground is a good recipe for ground imbalance and component damage.
See the online tools above.
No.
You realize that WDS is half duplex and therefore cuts your thruput in half.
At 1.25 miles and minimal antennas, my guess(tm) is that you'll get a
9Mbit/sec association with 802.11g. Thruput should be less than half at about 4Mbits/sec. Add WDS and it gets cut in half again to 2Mbits/sec.Yep. Your actually thruput will be highly dependent on the connection speed, which is dependent on signal strength (and quality), which is primarily dependent on antenna gain.
No, but there are side effects. Higher gain antennas have a much narrower beamwidth. As the gain gets high (over 15dBi), alignment becomes criticial. In the case of omnis, it's the vertical radiation angle that gets narrow. If there's an elevation difference, a rediculously high gain omni may have such a narrow beam width that the signal goes over the head of the intended target. Watch the beamwidth and downtilt specs carefully.
No.
No. The 125 degree angle is at the limit of sector antennas. Sector antennas have a different purpose. They're made of "area" coverage and not for point to point.
None. If you live in lightning infested areas, you might consider a lightning arrestor. The coax cable usually provides all the grounding that's necessary to prevent static electricity buildup (from the wind), but even that's minor.
Do the math (and use the SOM calculator). LMR-400 is about 0.07dB/ft. I use -1dB loss for each connector pair. Lightning arrestors lose about 1dB plus two connector pairs. If you want to use more coax, you'll just need to get a bigger antenna.
Probably not. The beamwidth at 1.25 miles is quite wide. Assuming a
24dBi antenna with a -3dB beamwidth of 5 degrees, the signal is about 570 ft wide. There's no way a 4" pipe is going to block all the signal. There may be some weird multipath effects, but I doubt if there will be any blockage.Jeff, I agree that 4 directional antennas would be a better option but I was wondering what your hardware choices would be for this compared to the wds solution. Obviously they have to be a bridge with ap capabilities or something like it.
Im not questioning your expertise, just trying to learn more. I am a wireless airhead student.
And my thought on the 2mbs using wds is that this gives all 3 users about
666mbs or so simultaneous use and if the objective is to share internet access this is plenty for most ISP speeds at 256 or 512mbs .If cost were a major factor here wouldnt WDS be the best solution? .
No, not so obviously. It can be done with routers. The problem is that it's complex and more expensive than WDS. A transparent bridge would NOT be necessary unless the OP wants all 3 locations to appear on the same LAN for network browsing. That makes lots of sense for a corporate remote office connection, but not much if you're just sharing the bandwidth with a few friends. So, let's take it one at a time.
wAN=IP from ISP WAN=192.168.1.2 LAN=192.168.1.1 LAN=192.168.5.1 DSL==[router]==[Access]==>> WAN [ ] [Point ] CH1 [Point ] [ ] [Point ] CH6 [ ] [Client] [ ] [ LAN ] [Mode ] [ LAN ] 192.168.1.100 192.168.5.100 192.168.1.101 192.168.5.101 192.168.1.102 192.168.5.102 etc etc Location #1 Location #2
WAN=192.168.5.2 LAN=192.168.8.1 from 254 GW = 192.168.5.1 NM = 255.255.255.0
Location #3 Router WAN IP = 192.168.5.2 LAN IP = 192.168.8.1 Clients IP = 192.168.8.3 -> 254 GW = 192.168.8.1 NM = 255.255.255.0
Note that this daisy chain type of system can extend indefinately. The midpoint (Location #2) has the advantage of being able to transmit and receive at the same time. Therefore max thruput is maintained.
Groan...
I'm not sure exactly how WDS works. I've only played with one WDS system and it was sufficiently complex to make measurements difficult. My guess(tm), is that connectivity between Location #1 and Location #2 are full speed as limited by S/N ratio, range, etc. Traffic to Location #3 goes full speed between #1 and #2, but half speed between #2 and #3 because everything has to transmitted twice with WDS.
It gets a bit messy when both #2 and #3 are downloading. Fair share says that traffic will be equally split at #1. Therefore, traffic to #2 will get 50% of the bandwidth. The rest gets cut in half by #2 WDS, so that #3 gets only 1/4th the bandwidth. I'm not sure about this, but it seems like a good first guess.
Since when has cost NOT been a factor? Good, Fast, Cheap...pick two. Yes, WDS is the cheapest. I don't think you want to hear my rant on wasted traffic, polluting the airwaves with duplicate transmissions, and efficiency (that also applies to mesh networks).
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