WiFi Antenna for point to point @1.65 miles? - Page 2 - Canadian TV, Computing and Home Theatre Forums
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post #16 of 45 (permalink) Old 2009-11-18, 11:36 AM
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Also, USB ones arent that pricey. Ive seen them at newegg recently for $10 - $12 on sale with free shipping.
Heres one on sale now at Newegg for $9.99 till 11/23/09 with promo code EMCMMMV72. $2.99 shipping for me. Its even got an external rubber ducky antenna that can be replaced with something better.

http://www.newegg.com/Product/Produc...P5D-_-33166023

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post #17 of 45 (permalink) Old 2009-11-18, 12:24 PM
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An "ethernet-WiFi bridge" is precisely what many short haul microwave links are. Some even use unlicensed spectrum, just like WiFi. They also use POE.
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post #18 of 45 (permalink) Old 2009-11-19, 04:16 PM
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Im very happy with my non dish biquad.
Picture:



I used galvanized sheet metal for the reflector, which allowed me to solder in the copper tube. Those spacers/holders are a cut up Bic pen and I use a thin piece of plastic in the middle to maintain feedpoint gap.
For the cable and RP-SMA connector, I got it from Newegg : http://www.newegg.com/Product/Produc...-053-_-Product

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post #19 of 45 (permalink) Old 2009-11-20, 01:40 PM Thread Starter
 
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Understanding the math of tx/rx

Okay, so I've done some reading and I think I understand the math/terminology when it comes to radios/antenna. Here is what I think I understand.

Line of sight loss over the air

This is a basic formula that takes frequency and distance and returns a db value of the loss of power in an ideal environment. Doesn't account for any other losses or reflections.

http://en.wikipedia.org/wiki/Free-space_path_loss

Simple formula is

loss = 20 x log10 (1.65 miles) + 20 x log10 (2400Mhz) + 36.58

So my loss in transmitting wifi over this distance would be -108.53 db

Antenna gain/cable losses in transmitter/receiver

If I take my Antenna gain and subtract any losses from the cabling to get the total gain out of the antenna/cabling, I would add this to the line of sight loss. Assuming I can get 12db at the receiver and transmitter for a total of 24db, my loss now would be

-108.53db + 12db + 12db = -84.54db

Transmitter power

Radios have a transmit power measured in dBm.

http://en.wikipedia.org/wiki/DBm

So a 100mW radio would be 20 dBm, so I would add this to the loss

-84.54db + 20db = -64.54db

Receiver sensitivity

Receivers have a sensitivity measured in dBm as well. A typical wifi receiver is -60dBm to -80dBm. So technically a wifi receiver should be able to pick up the signal using this ideal scenario.

--------------------------------

Is my understanding basically correct? I know there should be some leeway to account for less than ideal conditions.

As well, wifi receivers report RSSI. I'm assuming this value is in dBm so I can get an idea of how well my gains/losses are (or how close I'm to getting no signal).

--------------------------------

Last question, how does signal to noise factor in all of this?
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post #20 of 45 (permalink) Old 2009-11-20, 04:00 PM
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Signal to noise ratio determines whether you'll receive the signal or not. If there too much noise, the signal will not be detected properly. In analog TV the result was snow. With digital, it means loss of signal. Please note it's the ratio that's important. It's possible to have a very strong signal, but if the noise is stronger your reception will still suffer.
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post #21 of 45 (permalink) Old 2009-11-20, 07:43 PM
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You could also use a coffee can waveguide antenna, as shown here. I've heard of these working reliably up to 5 miles (can to can.) I first heard of these being used over 10 years ago, so it's a well established design. If the coffee can doesn't work, you can always upgrade to a pizza sauce can or beef stew can design.

p.s. "Road Warriors" use similar designs to eavesdrop on private networks. If you see a car with a coffee can pointing out the window, it's a sure sign they are sniffing out unprotected networks.

At 20 I had a good mind. At 40 I had money. At 60 I've lost my mind and my money. Oh, to be 20 again. --Scary
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post #22 of 45 (permalink) Old 2009-11-20, 09:08 PM
 
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Save the clutter and go with :
Two EOC-2610;s from EnGenius
There nice and compact 600mw 10dbi internal directional antennas
Power over Ethernet and no Signal loss,unless you want to add an external antenna to which is easily achieved as it has an external RP-SMA fitting under the hood.
http://www.engeniustech.com/datacom/...ls.aspx?id=246


Oh i just noticed you're in kitchener...not far from Belwood ont
This may be of interest these operate on the crowded 2.4Ghz and the less crowded 5Ghz band.
Available @ Tigerdirect not 2 far away.
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post #23 of 45 (permalink) Old 2009-11-21, 12:51 PM Thread Starter
 
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I've read about the cantenna projects but I'm not getting any good information from the blog posts - ie really technical over-my-head graphs and such. And the db gain just doesn't seem to be much better than a bi-quad.

The quad antenna looks good, combined with a parabolic dish - I think this would give me great results.

Another contender is the helix antennas. Lots of good information, and within my abilities to build myself. This article has some good information -

http://www.safe-pc.net/helical.html

Just trying to wrap my head around the SWR and dielectric constants and velocity factors.

I've mapped out some good line of sight points of interest (open areas with no obstructions) from my place. There is a good one 1/2 mile away. I think the next step would be to build a few antennas and make some observations of signal strength and wifi speeds.

ps - the new egg coupon code doesn't seem to work here in Canada. I'm going to check out the surplus store just around the corner from me for USB wireless adapters with rubber ducky antennas.
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post #24 of 45 (permalink) Old 2009-11-25, 12:25 AM Thread Starter
 
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Did some more reading and studying on the matter. Thought I would post this for anybody that is interested in long distance wifi.

First, I got my hands on a telescope to confirm a direct line of sight to my friends house. Surprisingly, even though I thought I had direct line of sight (looking a Google there were no big buildings in the way), there is a small 3 storey building in the way. Or more accurately my friends house is in a shallow valley.

No worries, with some careful measurements, I calculated a loss of about 25db for this lack of direct line of sight and I think I'm still within limits of being able to connect.

A great website I came across that can calculate all this stuff is here -

http://www.qsl.net/pa0hoo/helix_wifi...udgetcalc.html

------------

Finding the right radio was tricky. I looked at the USB wifi adapters however these things are all for Windows PCs. I wanted more diversity, something perhaps OS neutral. Most of my computers are Macs, then linux and I only have one Windows machine which is a laptop and I only use that to view video streams (when it's not updating Windows :P )

Power over ethernet radio was the logical choice. And I came across some nice options from a company called Ubiquiti Networks. In particular they have a nice radio called the Bullet.

http://ubnt.ca/home?page=shop.browse&category_id=9

Reasonably priced at $49 CAD for a 100mW radio. A little more for 800mW radio. The radio features a N type connector on one end and the ethernet connector on the other in a barrel shaped form factor. A segmented led display show the power levels so that comes in handy when aiming the antenna. This radio simply connects to any type antenna (biquad, helix, or dish)



Looking at the insides, the N connector solders directly to the board so there will be no losses in any cabling. So I should have very little loss.



Another thing that is nice about this radio is it is fully configurable, via a web browser interface, to be an access point, bridge, router, etc. It comes with a linux SDK for any custom work I want to do but I don't think I'll need to. It's also built from the ground up for long distance wifi, so you can easily adjust tricky items such as packet sizes and delays to wait for ACKs because of the distance with a simple 'distance to transmit slider' on the web interface.

I'm going to do a bit more reading a searching the web for as much info as possible, but I think I'll be ordering up a couple of these radios - unless I find something even better!

And I still can't make heads or tails of Industry Canada's limits on wifi transmissions, so I'll have to give them a call to find out what my legal unlicensed limit to transmit is.
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post #25 of 45 (permalink) Old 2009-11-25, 08:18 AM
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Those "Bullets" look interesting. I see they also have higher power levels too. I wonder what they do about weatherproofing the ethernet side? You may also want to use shielded exterior grade ethernet cable.
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post #26 of 45 (permalink) Old 2009-11-26, 06:12 PM
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And I still can't make heads or tails of Industry Canada's limits on wifi transmissions, so I'll have to give them a call to find out what my legal unlicensed limit to transmit is.
Right. Give them a heads up that you might be doing something illegal. I think the guidelines and specs are published. Due to antenna gain, your installation will bend the rules somewhat. I have a feeling that unless you go over 100mw, nobody will notice. I would be most concerned about interference with/from other wireless devices in that building. Maybe a mast on each end will clear it.

At 20 I had a good mind. At 40 I had money. At 60 I've lost my mind and my money. Oh, to be 20 again. --Scary
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post #27 of 45 (permalink) Old 2009-11-26, 08:19 PM Thread Starter
 
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Unless I'm mistaken Industry Canada is quite generous when it comes to output power. In fact, it seems to good to be true kind of output power!

Here is what I think I know-

main link on industry canada site -

http://www.ic.gc.ca/eic/site/smt-gst...g/sf08655.html

The wifi radio has to comply with RSS-210

For systems employing digital modulation techniques operating in the 902-928 MHz, 2400-2483.5 MHz and 5725-5850 MHz bands, the maximum peak conducted power shall not exceed 1 W.

Systems in the 2400-2483.5 MHz and 5725-5850 MHz which have an e.i.r.p. above 4 W are permitted only for point-to-point systems (i.e. point-to-multipoint systems and multiple co-located transmitters transmitting the same information are prohibited from exceeding 4 W e.i.r.p.).

Point-to-point systems in these two bands may use higher e.i.r.p. as necessary for satisfactory operation provided that the higher e.i.r.p. is achieved by employing higher gain directional antennas and not higher transmitter output powers.


Max output is 1 W, max e.i.r.p. (the output of the radio + antenna gain) is as much as I need to go point to point, provided I use a better antenna and not a more powerful transmitter.

Handy link to make sure the wifi radio complies with RSS210

http://www.ic.gc.ca/app/sitt/reltel/...ch.do?lang=eng

The Bullet radio @977mW has been certified by Industry Canada.

------

So, a quick call to industry canada will clear this up in my mind.
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post #28 of 45 (permalink) Old 2009-11-27, 05:32 PM
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Surprisingly, even though I thought I had direct line of sight (looking a Google there were no big buildings in the way), there is a small 3 storey building in the way. Or more accurately my friends house is in a shallow valley.
If the building is made with a lot of metal, you may be effectively completely blocked. Any chance of mounting both antennas high enough so you do have line of sight ?
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Max output is 1 W, max e.i.r.p. (the output of the radio + antenna gain) is as much as I need to go point to point, provided I use a better antenna and not a more powerful transmitter.
Yeah, 1000 mw limit is fine, get the 800mw unit.

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post #29 of 45 (permalink) Old 2009-11-27, 06:21 PM Thread Starter
 
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"If the building is made with a lot of metal, you may be effectively completely blocked. Any chance of mounting both antennas high enough so you do have line of sight ?"

Looks like it might be metal - here is the building in question.



I have been using elevation maps to calculate how high the antenna must go to clear it. Quick calculations show an antenna 25ft from the ground (easily done with a chimney mount) will clear it. My next step is to borrow an accurate GPS unit to get super accurate elevations. I tried today with my iPhone's built in GPS but it's just not all that accurate for getting elevations.
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post #30 of 45 (permalink) Old 2009-11-28, 11:24 PM
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A 100mW radio with a 10dB gain antenna is 1W e.i.r.p. 100mW with 16dB gain would be 4W e.i.r.p. That doesn't take things like line loss into account.

At 20 I had a good mind. At 40 I had money. At 60 I've lost my mind and my money. Oh, to be 20 again. --Scary
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