wireless signal through trees (what does line of sight" mean)

On Dec 11, 1:06=A0pm, david fraleigh wrote: =A0I am wondering if they are somehow

This may well be an issue for you.

Look up Fresnel distance. (I don't know much about it.)

Someone with a clue will likely be along in a minute. There have been discussions on this in this group previously.

Would power line networking work for you?

Otherwise run some kind of cable. I understand that for the pusposes of lightning protection you might need to use fibre.

Its not the trunks that are the problem, it is the leaves. They will kill the signal stone dead. You really do need a clear, as in empty, line of sight, and it is not a tunnel, but rather two cones that meet at the middle (the wide bit of the cone where they meet). This is known as the fresnel zone, and it must be clear. Assume that where the cones meet it must be several meters across.

David

It is possible, but only with at least one directional antenna that has some gain. Would it be too much trouble to disclose what hardware you're using?

Optical line of sight and radio line of sight are visualized somewhat differently. Radio line of sight requires clearances well beyond optical line of sight in order to prevent edge diffraction and work reliably. The clearance area is called the Fresnel Zone. For 300ft and 2.4GHz, the clearance radius should be about 18ft.

(Use 300/5280 for converting 300 ft to 0.0568 miles). What that means is that at midpoint, everything including the ground, has to be clear for an 18ft radius. It also implies that the antennas have to be 18ft above the ground to prevent the ground from becoming part of the problem.

Incidentally, you can get a clue as to what it does to the signal with this:

At 2.4GHz, the signal does the same thing. It wouldn't be a problem if you could reliably place the end points at the maxima. However, that's not going to happen because if ANYTHING moves even a fraction of a wavelength, so moves the pattern.

If the trees were near either end point, it might work. Note how the Fresnel Zone narrows as it approaches each end. However, in the middle, it's a dubious proposition. When we used to have a neighborhood wireless LAN, I was shooting to one neighbor between two large redwood trees, with about 4ft between trees, at midpoint over a

The signal is just as strong as it left the transmitter. It's just the less of it arrives at the other end of the link.

Yes. See explanation of Fresnel Zone diffraction.

A small hole is not going to do it. I've succeeded where I had about a 50% of the Fresnel Zone radius, but had to add some antenna gain to the puzzle to insure reliability. It also depends on the type of trees. Going through water filled trunks and branches is impossible. Going through thin leaves, needles, and a sparce forest is possible with enough antenna gain. With your arrangement, you will probably be able to get a signal through a hole, but you will NOT be able to keep it stable. The signal level will vary radically as things move around.

If this is through the woods, I suggest you look into waterproof CAT5 cable or fiber optics. I don't think that wireless is going to do the job for you. I have a few of these installed and find the critters are the main obstacle. Flex plastic lawn sprinkler tubing works well to protect CAT5 (if you keep the water out) through the forest floor. Shallow trenching also helps.

Also, if you ask such questions in the future, please try to include some numbers. When general theory questions are nice, it's often easier to run some calculations. In this case, a link calculation would be necessary to test if it is even possible to obtain a 300ft range with your unspecified equipment without the trees:

I'm trying to follow along and maybe learn something, but not getting very far. When I plug in 0.0568 miles and 2.4GHz, I get a radius of

Hopefully, the OP will get more of a clue from this second link than I did. I wasn't able to learn anything there about when something encroaches upon the Fresnel Zone. (Probably says a lot more about me than anything else.)

Sorry. You're correct. I plugged in 0.568 by accident. Thanks.

The Fresnel Zone radius should be 5.54ft. 11ft diameter is still more then the 2ft space between the trees. Also, the antenna need only be

Another calculator, that doesn't require dividing by 5280 to convert to miles:

or a massive overkill calculator:

For longer paths over more rugged terrain, I use (free) Radio-Mobile software:

etc...

I thought an optical analogy would help. That was probably a bad idea. See photo at:

This is what a zone plate looks like (highly magnified). Operated in reverse, this is also roughly what happens to the signal as it goes through a circular aperture. Think of the light and dark areas as signal strength. The white areas are where the various wave components reinforce to yield a strong signal. The dark areas are where they cancel to form a null.

More:

Wireless - Fresnel Zones and their Effect Or 'Why Line of Sight is not enough'

Radio Mobile - RF propagation simulation software

Questions?

Thanks, that makes sense now.

Ahh! I see now what you were trying to illustrate with this. Thanks for taking another run at it.

Not from me, thanks. I have a bunch of reading to do. Besides, I'm just a parasite on this thread. I'll step aside for now and leave it for the OP to drive it forward or not. Thanks for the quick reply.

It's simple really , at night point a torch along the desired path , it offers an indication of the possibilities by lighting things that might cause problems , very rough but it helps visualisation for some , basically is you don't have vegetation in the way it's worth a survey to establish the maybe factor but remember leaves tend to fit into the wavelength you are playing with and will act as a blocker with increased moisture or some rain just when you need it

NOTE: Posting from groups.google.com (or some web-forums) dramatically reduces the chance of your post being seen. Find a real news server.

There aren't that many moderated newsgroups on Usenet. The monthly post of "List of Big Eight Newsgroups" to news.announce.newgroups, news.groups and news.lists.misc listed 2218 groups in the comp.*, humanities.*, misc.*, news.*, rec.*, sci.*, soc.*, and talk.* hierarchies and identifies only 228 as moderated (a number of those are essentially dead). While the average news server will carry at least ten times as many newsgroups (the server I'm posting through claims to carry 111,000), there aren't that many that are moderated.

I didn't realize this group was being spammed - but now that you mention it, looking at the logs show 135 of the 170 posts this month up to 14:00 UTC on the 14th hit the killfile, and were silently discarded so that I never saw them.

Yeah, but you were probably using a real news reader and connecting to a news server, not a web interface reading from google (or deja-news). Try using one of the dozens of free news servers, and using a news reader with a filtering capability. See the Usenet newsgroups alt.free.newsservers and news.software.readers for hints.

Old guy

Google: "The Nonexistent Microwave Absorption Peak of Water"

In the first edition also, on page 154 :-)

Interesting. That would seem to indicate that my favorite method of blocking RF, a wet towel, doesn't work. Yet it does. Of course, since water now does not attenuate RF, we should be able to communicate under water at 2.4GHz. Last time I checked, submarines had to use about 10KHz RF in order to communicate as higher frequencies just didn't seem to penetrate. (Note that I'm talking about liquid water, not water vapor or fog).

I'll try it again with a dish antenna and a wireless link just to be sure.

I just did a rather quick (and stupid) test. I wrapped my iPhone 3G in a wet towel and ran yFyLite (Netstumbler clone). Signal strength for my AP is about -34dBm. I can also see a total of 4 systems (including my own). Wrap it in a wet towel[1], and my signal strength drops to -50dBm (with major variations due to having to look at the display through a small leaky hole). The other 3 system disappeared completely. Unless cotton towels have somehow become an RF absorber, I would think that water is doing something to the signal.

I'll do a better test later today.

================================== Consider a plan "b".... consider, how does the shop get it's power? while line of site may be okay now, whats gonna happen in the spring/summer when leaves happen? In the summer/fall when it rains? or in the winter if it snows?

i use powerline networking from my home router, to the shop on the powerline (basic ethernet extension) and another wap in the shop to give me wireless (total cost about $150)

have a coax cable for tv to your shop? (I do for football games), they also make coax networking (works similar - one in the house, one in the shop and a second wap/router)

while i don't necessarily promote this specific manufacter, they do have some good info..

I am using the Netgear MCA1001 coax system in my home and it works great.

Peter Pan wrote:

I persuaded a friend to try powerline, based on Peter Pan's previous recommendations. Prior to that, he had been convinced that he needed to drag some Cat5 through the walls, since WiFi wasn't working.

He also wasn't sure about "Mac" compatibility, which I tried to assure him was a given.

He had an unused CTV outlet in that room, so that coax adapter is an interesting new twist that I hadn't noticed before.

That's a MoCA adapter.

Basically, it's a coax cable RF modem. With it, you can share the coax cable with CATV, satellite, or whatever. Plenty of others to choose from:

What I don't like is that they're still a bit expensive and that you need two of them to make things work. What I like is MoCA 1.0 does

If he had a dedicated (i.e. not shared with anything) CATV coax run, he could have used it for 10baseT-HDX CheaperNet, using two old ethernet hubs or transceivers that have the BNC connector, two T connectors, and two 50 ohm terminators. Yes, I know the coax is 75 ohms, but it works quite nicely for everything except extremely short cable runs (i.e.

Done. I hung a 24dBi barbeque grill dish onto my balcony rail, attached a Ubiquiti Bullet 2 radio (scheduled for installation on Friday) to the back, connected my laptop, and found a neighbors wireless access point. I knew the WEP key (yes, it's crappy WEP encryption) so I connected. -35dBm signal strength.

I then took a soaking wet bathroom rug that I idiotically left out in the rain, and hung it over the dish. Why a rug instead of a towel? Because it holds more water. I also placed half a paper cup over the dipole feed to avoid any detuning effects. The signal dropped to

-62dBm but started increasing slightly as the water dripped out of the rug.

I then covered only half the dish and got -45dBm, a -10dB drop. I would have expected only a -3dB drop, so something is still not quite right. As a control, I grabbed a similar but dry bathroom rug out of the bathroom and hung it over the same dish, in the same manner. The signal moved around a bit, but basically it was the original -35dBm average.

I can take some photos if you want, but later.

Conclusion: Dry rugs do not attenuate 2.4Ghz. Wet rugs attenuate substantially.

What sold me was it appeared to be about 3-1/2 times faster than powerline. Also I felt there would less chance for somekind of interference. I have not tried connecting wireless to the upstairs unit it but it should work. One reason I had to go this direction is with the location of my cable modem and wireless router downstairs I could not receive wirelessly in the upstairs front rooms.

Jeff Liebermann wrote:

Meanwhile, at the alt.internet.wireless Job Justification Hearings, Jeff Liebermann chose the tried and tested strategy of:

If you've got some kind of rug problem, I think you should seek medical help.

Hint: I have no job. No sane company would hire me.

No problem. Despite advanced androgenic alopecia, I don't wear a rug. I prefer to wear a tin foil hat, which prevents RF induced brain rot and also improves my cell phone reception:

For formal ocassions, I use a collander:

which also doubles as an antenna ground plane.

Official excuse. I just finished reading the book:

My brain has turned to mush.

Is it line of sight, or sign of light?