Close, but no line of sight.

Jaden

Hi all,

2 Houses, 300 meters apart. Big hill in the way. A watertank on top of the hill is in clear line of sight to each house. Can't get power to the hilltop, so what are my options for a wireless link? I remember something about mesh repeaters. Can anyone point me in the right direction?

I have the accesspoints, routers, etc all sorted, all I need is a way for each wireless router to see the other.

Ideas?

bminish

Originally posted by Jaden
Hi all,

2 Houses, 300 meters apart. Big hill in the way. A watertank on top of the hill is in clear line of sight to each house. Can't get power to the hilltop, so what are my options for a wireless link? I remember something about mesh repeaters. Can anyone point me in the right direction?

I have the accesspoints, routers, etc all sorted, all I need is a way for each wireless router to see the other.

Ideas?

passive repeater.

take two high gain antennas (suggest 23dBi mesh grids) wire them up back to back and mount on the hill aim one at one house aim the other at the other hose

Passive repeaters are not all that efficient, it only reradiates some of the power it intercepts and at that distance that's not a lot.. so at the house ends you are going to need to use high gain antennas pointed at the antennas on the hill so that theres a very good signal presented to the passive repeater setup otherwise there won't be enough left on the other side to do any good

23dBi antennas need to be pointed fairly accurately so align them carefully or it won't work
get your router and access point as close as possible to the antennas to reduce the impact of cable losses

.Brendan

Capt'n Midnight

If passive repeators
2 large MMDS dishes with N connectors - you will need a small coupler in between to link the two together.

Best to try for a bounce first - if there are large glass .metal surfaces eg barns you could try that. - perhaps even off the water tower.

If the top of the hill is not to high above the line of sight then a link might be possible since the distance is so short (you are relying on diffraction etc.)

If you can run a cable to the tower you could use POE to have one of the units powered up there.

bminish

Originally posted by Capt'n Midnight
If passive repeators
2 large MMDS dishes with N connectors - you will need a small coupler in between to link the two together.

If you can run a cable to the tower you could use POE to have one of the units powered up there.

VBnets will sell you 2 x dishes 1 with female N one with male N

If you can run cable how about buying 3 rolls of cheap sat tv coax (CT electric sell it for ~ 22 Euro / 100m last time I bought some) and wire the 2 access points together.

Yes it's a mismatch (75 ohm coax instead of 50 ohm coax but even before cable losses this won't be a problem) but you will have enough signal left after ~70dB of losses @ 300m to allow a solid connection @ 11 mbs

Cheaper than buying 4x high gain antennas to try the passive repeater approach

.Brendan

Capt'n Midnight

ROFL - linking two wireless AP's with 300m cable

Be careful though - the recievers may not be able to handle that much power (ie. don't test with short lengths of cable)

Actually if you can run cable - get some shielded Cat5e and a pair of gigabit cards - it might just work (or put a small hub in the middle and power it from the cable)

Passive receiver is non-runner really.

Capt'n Midnight

Hang about - lasers and a mirror on the water tower.

there was a DIY version on the interweb using AUI connectors on old 10Mb cards, some lenses and laser pointer pens.

bminish

Originally posted by Capt'n Midnight
ROFL - linking two wireless AP's with 300m cable

Be careful though - the receivers may not be able to handle that much power (ie. don't test with short lengths of cable)

Actually if you can run cable - get some shielded Cat5e and a pair of gigabit cards - it might just work (or put a small hub in the middle and power it from the cable)

Passive receiver is non-runner really.

actually it won't be a problem by a decent margin, here's the math


for the output of card A lets assume 15dBm (30 mW )

loss of cable ~ 70dB ( a ballpark figure ), remember this TV coax is a lot more lossy than LMR-400 (but MUCH cheaper..)

at the other end we have 15 - 70 = -55dBm
generally you need better than ~ 75 dBm to manage 11 Mbs with the cheap 'n nasty wifi kit so wit this setup you have a link margin of around 20 dB so you might manage another 100m or so of coax before the whole thing has to drop down to 5.5 Mbs to hold the link

Now if you had a 20 dBm (100mW) Access point add 5db to your link margin above.
most wifi cards will start to have problems at around 0dBm but I would not expect damage to occur at this level

300m is a bit far for ethernet, generally it falls apart in a nasty way once you go over the segment length (Which I think is around 100 m ) you could always use Gb ethernet over fibre it's cheaper than you think and the performance rocks :-)

.Brendan

Capt'n Midnight

Fibre - D'oh

Would you get extra distance by forcing gigabit cards into 10Mb Full Duplex mode ?

Over 300m of cable should be Ok - it's just too tempting to try it over a short length..

bminish

Originally posted by Capt'n Midnight
Fibre - D'oh

Would you get extra distance by forcing gigabit cards into 10Mb Full Duplex mode ?

Over 300m of cable should be Ok - it's just too tempting to try it over a short length..

No it's not a problem caused by cable losses, it's all to do with the timings. the protocol expects to hear a reply within a given period of time, if the segment is over 100m it doesn't and it all falls apart horribly.

these segment lengths can be got around by using a switch every 100m since the timings will be between the PC and the switch , the switch and the next switch, the switch and the PC
this won't work with hubs since a hub doesn't regenerate packets. If you are using a hub the total distance between any 2 pc's on the network must be less than 100m or bad things will happen


.Brendan

spongebob

unlike Cat V cable which works to 100m you will find that 2 x 1000Base SX Gigabit cards (or GBICS if your switch will take them) will work in crossover mode up to 550M which is long enough.

300M of single mode fibre is all you need apart from the cards and hup, 1 Gig Full Duplex to the neighbours. I'd say €800 or so.

Are there any hungry sheeps on that hill though ?

M

Jaden

I have it sorted.

2 pringles cans on the watertank, and now the two access points can see one another.

Man, I'm good. Thanks for all the help, useful stuff.