900 metre shot not working

Hi all.

I am trying to create a wireless network from my office in Grey Lynn to my home, which is about 900 metres aware with a direct line of sight. A friend who lives in the area also wants to connect, so we're using a Micronet AP (http://www.micronet.info/Products/Wireless/SP918.asp) with a 13dBm maximum power output at the office, connected via 10M of 50 ohm coax to an 8dBi omni (http://www.micronet.info/Products/Wireless/SP920M.asp). Client end is a PCI WLAN card connected via 10M of identical cable to an 8dBi uni (http://www.micronet.info/Products/Wireless/SP920D.asp). The client and the AP simply cannot see each other over the 900M distance, however we have verified that each individual part is in working order.

The only thing that we can think of is that our shot is on a direct line between the sky tower and the transmission mast in the waitakere ranges.

Does anyone have any ideas about problems or what we're doing wrong?

Thanks, James.

a total of 20 metres of coax is quite a bit. Is it any good? Have you looked at the loss per metre for it at 2.4GHz?

Have you tried netstumbler on the antennas to check if they give you much better performance then the inbuilt ones? With 10m of cable, you will prob find that the cable is un-doing any good that the antenna does.

I was assured that it was excellent quality low-loss cable (it better be, it cost about $100 for each 10 metre segment!).

but do you have the loss per meter at 2.4-2.5GHz? Without that, you cant really figure too much out as to why its not working. Can you see any networks on the end with the PCI card?

What sort of cable are you using? I notice you say it's 50 ohm coax, but is it RG-213 or something?

Just want to do a bit of a calculation to see how much loss would be incurred (in theory)

All I can tell you is what's written on the cable: HDF 400 LOW LOSS 50 OHM COAXIAL CABLE COMMATE/PEWC 8D

I'm guessing HDF 400 has the same loss as LMR 400 (got this info from some website)? which is about 6.8db/100ft. So your losing about 2.1db at each end of the link, from the cable? So you've got a transmission power of 13db, and a antenna gain of 8db, and a loss of 2.1db, so you end up transmitting with 18.9db (or 77.62milliwatts of the allowed 4000milliwatts) of power (not counting connector loss and stuff). Correct me if im wrong, but this doesnt seem enough to do a 900meter link.

I bunged all the information into http://www.zytrax.com/tech/wireless/calc.htm#system

It says you'd have a theoretical margin of about 8.69db. From what i know you're ment to have a margin of about 15-20db for a reliable link.

*Shrugs*

Just as an idea. If you put the AP on the roof with a PoE device and make your antenna cables as short as possible. The use a second AP with the same setup both with directional entennas you should get the range you want.
Since you are in Auckland let me know if youre interestd in taking a look at my design. I use CHEAP off the shelf gear and have hit ranges of atleast 1.5Km LOS.
Both ends had a "Roll My Own" Antenna one an Omni the other a BiQuad.

andrew

Good news everyone!

We managed to get this go, but not with the 8db antennas. I scored a 24db omni and a 24db parabolic for free from a client. Anyway, we're all up and going.

Thanks for your help, everyone.

24db omni?? WTF? Got pics?

Good to hear you have had sucess, and if your client has any more antennas to get rid of, im sure you will be able to sell them to someone from here..

it's just a really really long white stick :)

actually, we might have to sell off the 2 x 8dB unis and the 8dB omni to recoup our losses. Contact me if your interested.

its just the biggest I have seen is a 15dBi omni.

Im quite happy with the little 16dBi Vagi I got. Can have it in the car and pinpoint APs easily

indeed 24dbi omni, wtf?

afaik 15dbi+ is for directional aerials, not omni directional

Just so you all know, the 8db antennas are now listed on trademe.co.nz.

http://www.trademe.co.nz/STRUCTURE/auction....asp?id=5354109
http://www.trademe.co.nz/STRUCTURE/auction....asp?id=5354164
http://www.trademe.co.nz/STRUCTURE/auction....asp?id=5354351
http://www.trademe.co.nz/STRUCTURE/auction....asp?id=5354434
http://www.trademe.co.nz/STRUCTURE/auction....asp?id=5354548
http://www.trademe.co.nz/STRUCTURE/auction....asp?id=5355385