Wide Area Wireless on a Shoestring Budget?

wkytechhead asks: "My father owns a greenhouse operation that covers a few dozen acres. He has a number of greenhouses some up to 1000' plus apart that he would like to network. Currently he is using a HomePNA based network via regular RJ12. He has decided that he would like to go at least partially wireless. Some consideration has been given to using the backbone with fiber convertors, but he would really like to do full wireless. I have checked into homemade and commercial 'Cantennas' but I am not sure if they are worth the money. How would my fellow geeks go about wirelessly networking a large outdoor area for as cheap as possible?"

Comments

24dBi Point To Point Antennas for around $55 each

[codermarc]

You should check out these antennas from HyperLink Technologies. For outdoor applications these should work very well for you.

DSL

[Helix150]

Some golf courses and other large areas use remote-DSL for such links. Maybe that would apply to him? Many cisco DSL modems can be operated in server mode, only downside is you must run RJ12 separately to each location.
Otherwise, run ethernet?
if you are going to go wireless, get some good APs and sector antennas, or alternately setup a bunch of repeater stations that use different channels to avoid interference.

Minidishes

[EdZ]

minidishes (commonly used in the UK for digital satellite television) can be easily adapted to use a WiFi signal boosters. They're highly directiuonal of course, but ranges of 2 or more kilometers LOS are not unknown. Plus, no boosting equipment is required, just a modification to the antenna.

That's not going to be easy

[spawnofbill]

For outdoors, I think your SOL, but for inside the greenhouses, investigate something called "leaxy coax." It's basically a coaxial cable with little to no shielding, and a couple of companies have recently made it usuable with 802.11b/g.

Re:That's not going to be easy

[Anonymous Coward]

I observed leaky coax tests at a previous company, and it didn't seem to work very well. It seemed to work for the AP transmit, but the return signal was week (imagine, the signal recieved at the far end of the leaky coax, it is leaked all the way back to the AP).

Re:no necessarily cheap

[billhuey]

http://www.seattlewireless.net/index.cgi/AntennaHo wTo

Is a WiFi antenna howto and I build the can-waveguide out of two tomato sauce cans with an N connector. It totaled to about 5 bucks worth of parts and works very well. The tuning for it though might be off and I hand redid with a sheet metal snipper.

This is what I use for a 1000' link

[fatboy]

This is our amateur radio repeater that uses VoIP to link to other repeaters around the world. The link is 802.11b

Here is the AP that provides access.

Nothing special to do a 1000' link. Just a parabolic grid antenna on the client side.

Here are some parabolic grid antennas.

I was the IS manager for a large greenhouse....

[Jailbrekr]

The first question you have to ask yourself is what you want to get out of the network. Do you want full roaming capabilities, or do you want localized points of presence in every greenhouse? Are you wanting to implement VoIP? Network aware control and monitoring systems?

If you are looking for a setup like what I had (points of presence in every greenhouse), all you need are some cheap(ish) base stations for the endpoints, and a kick ass 24dB omnidirectional antenna for the master base station at the head office. Build small networks at each pop and bango. If you want roaming in a few areas, throw in a small consumer wireless base stations and hook it up to the pop.

If, however, you are looking at using the network for business critical voice services or control and monitoring systems, then you had better look seriously at fiber (fiber ring preferably). You never know when some bird lays a massive shit on the antenna. Wireless is simply not as reliable as wired.

Re:24dBi Point To Point Antennas for around $55 ea

[Cylix]

Or you can search froogle for them
"2.4 ghz parabolic antenna"

Lowest price is around 33$ for a 15dbi gain. 50$ is about right for a 24dbi gain. Though a parabolic is only going to be truly handy for sight to sight. They do have low cost omni directional antennas. This is difficult to advise without knowing the layout.

ie, possibly sight to sight parabolic for the backbone link and then omni's distributed throughout.

If you are really worried about distance, just dig up a router that can be tweaked for a bit more output power.

Now, if completely unsure of what your needs are, here is a handy calculator to help you figure your distance needs out.

http://www.signull.com/fsc.php

For the uninformed, cable loss is going to be calculated by the amount of signal loss expected when using some portion of cable from the transciever to the antenna. It should be expressed quite clearly on type of cable you are going to be using.

There are also some common models output numbers listed there as well.

That really sums up everything. It should be quite cost effective to implement a few antennas and a cheap 802.11b setup.

Re:That's illegal in the US

[j1m 5n0w]

http://www.access.gpo.gov/nara/cfr/waisidx_03/47cf r15_03.html

[Code of Federal Regulations]
[Title 47, Volume 1]
[Revised as of October 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 47CFR15.23]

[Page 693-694]

TITLE 47--TELECOMMUNICATION

CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION

PART 15--RADIO FREQUENCY DEVICES--Table of Contents

Subpart A--General

Sec. 15.23 Home-built devices.

(a) Equipment authorization is not required for devices that are not
marketed, are not constructed from a kit, and are built in quantities of
five or less for personal use.
(b) It is recognized that the individual builder of home-built
equipment may not possess the means to perform

the measurements for determining compliance with the regulations. In
this case, the builder is expected to employ good engineering practices
to meet the specified technical standards to the greatest extent
practicable. The provisions of Sec. 15.5 apply to this equipment.

Re:24dBi Point To Point Antennas for around $55 ea

[rcw-home]

how do you figure it out?

Use a link budget calculator. (The link is one I just found with google).

Basically, you need a certain signal to noise ratio for a digital radio connection to work at all at its lowest speed. Increased signal to noise ratios get you more speed and some margin of reliability.

Signal decreases with the square of the distance. If you double the distance you'll have one quarter the signal, or 6db less (decibels are logarithmic - 3db is a ratio of 2, 10db is a ratio of 10). So, everything else being equal, you'd need 6db more gain on the antenna at either end to get the same results.

For your particular scenario you'd probably be fine with just a couple cantennas or other moderate-gain antennas.

One thing to watch out for when shooting through trees is that they may not have leaves now but they will in a few months!

Re:24dBi Point To Point Antennas for around $55 ea

[Cylix]

A lot of those wireless cable antenna are actually in the 2.5ghz range.

Still, they will work just fine, with some gain loss...

Here is a smaller article on the matter... to adapt one. (kinda helpful if you really really don't know what you are doing)

http://www.qsl.net/n9zia/wireless/page04.html