wifi antenna in the mountains

Sheesh, how about just using a passive repeater ??

Why not just get satellite internet? Is this a hobby project? Anyways, it seems that power is your problem here. I am interested inseeing what people come up with.

K

Exactly what I was thinking. getwilde, just take two decent antennas, grid parabolics would be nice and not necessarily all that expensive, and hook them up with a bit of coax running from one antenna to the other. Aim one at your house, one at the WISP. No electronics involved so no need of elecjuicity.

"Me" schreef in bericht news:qabff.3606$ snipped-for-privacy@news20.bellglobal.com...

I agree. Is solar and/or wind power and a car battery a viable option?

Paul

Do you have any idea how large the passive reflector will need to be at 600ft in order to make this useable? At 2.4GHz, the highest gain antenna is about 24dBi with a 7 degree beamwidth. At 600ft, that beam is 74ft wide. With a 45 degree tilt angle, that's a 103 x 103 ft diameter reflector. Anything less will result in corresponding loss of signal. Half the size = 1/4th the area = -12dB loss.

I can work the numbers in detail if you want, but such arrangements never work at 2.4Ghz. See references under "periscope antennas".

Oh, now you've got me excited. I figured juice would be required between antennas (but I'm still trying to learn all of the principles involved). If I were to build a passive setup like Roger explains, do I decrease range by not having power? The 4 or 5 miles to the Acess Point worries me a bit.

So, am I thinking about this right...? To increase range: Is adding an amplifier at my house the best way to increase the outgoing signal, even though it will be passing through the passive antenna? Likewise, if the grid parabolic pointed at the WISP is larger, is that the best way to increase incoming reception? (Assuming I build the whole setup well)

Incidentally, yes, solar and a car battery are options, but a huge hassle if I can avoid them (and I would run the risk of having them stolen at some point). But if I were told that power at the middle antenna is the only way to insure good range, then I'd definitely explore that further. I'd even be willing to march up there every few weeks to replace batteries (skip the solar power thing altogether), if power requirements were low enough to make a small battery rack an option.

This is good news. This should be no problem.

Wrong on both counts. I've run all kinds of power through the forest. As long as you don't cross any major boundaries (roads, property lines, etc), you're fine. Low voltage power is not considered a fire hazzard. Xmas tree lamps draw more power and get hotter than a typical access point.

In addition, you can run up to about 1000ft of CAT5 at 10baseT-HDX speeds. I've scribbled several postings in this newsgroup on the topic. You can also use coaxial cable for about the same distances using RG-6/U and 10base-2 using media converters. Of course, you can also use fiber, but that's a bit more expensive and overkill.

Let's grind the numbers for running power up the hill. I'll use 700ft because there will probably be some snaking of the wire. I'll assume you'll use an ethernet bridge radio or one that supports client mode. I suggest a Linksys WRT54G (NOT v5) with DD-WRT firmware. The nice part of this device is that it has a very wide range switching regulator which will run the box on anything between about 4 and

18VDC. This is critical for delivering power. I forgot how much power it draws but I'll guess about 8 watts max.

Start with some higher voltage at the house, run 600ft of wire, and want at least 6VDC at the access point, at a current drain of about

1.3 amps (at 6VDC). So, how much voltage does it require?

Well, you can almost do it with CAT5 cable, which has a resistance of

3 ohms per 100ft per conductor. With 2 conductors in parallel, that's 3 ohms/100ft loop resistance. 600ft would have 18 ohms loop resistance. The approximate current drain is: 8 watts / 6 volts = 1.33Amps Therefore, the voltage drop across the cable is: 1.33A * 18 ohms = 24VDC. So, if you start with a 24VDC power supply, and take the loss in the cable, you get 6VDC at the WRT54G.

Unfortunately, the power dissipated in the cable is too high: 1.33A * (24 - 6V) = 24 watts It won't melt the cable but it will get quite warm. Bad idea.

So, we use heavier cable. I suggest outdoor low voltage UV proof rubberized cable used for garden flood lights and outdoor low voltage wiring. It's typically about #14AWG which is about 0.25 ohms/100ft per conductor.

Grinding the same 600ft length at 1.33A, I get: 1.33A * 3 ohms = 4 volts So, we start with 10VDC, lose 4 volts in the cable, and end up with 6 volts at the WRT54G. Power dissipation is: 1.33A * (10 - 4v) = 8 watts which is still a bit high, but workable.

In reality, starting with 12VDC makes more sense. The current drain is somewhat less than 1.33A. 8 watts over 600ft is a bit too high so I would use some heavier wire if available. The important point is that it will work by running a power cable and either CAT5 or RG-6/u if the radio has a wide range of acceptable power supply voltages.

I can answer the RF questions below if running power is unacceptable.

Ack! As a satellite internet user, I'd jump through more hoops than the OP is facing to get service from a WISP!

OK, that's an obstacle. You could probably solve it with a solar panel and a battery - but theft could be a problem. It would still be my choice.

No, it isn't. I know the standard specifies 100m, but Jeff will tell you he runs it 1000'

I've considered satellite, but I'd prefer higher speeds, less latency, and lower costs. Not having a phone line might also be an issue... but I'll only explore that further if I can't get this wi-fi approach working.

Thanks to everyone for the great ideas. Jeff, thank you for your detailed response. It's obvious that you're very knowledgable in this area.

Regarding passive antennas: A bit more research shows that they're commonly referred to as "Passive Reflectors". Google reveals all sorts of information about them. With guidance from XReXXwifiX, I've located Cringely's claim to success

However, Jeff, your response about the size area of the signal after travelling

600 feet makes a lot of sense, and really brings into question Cringely's credibility. Unfortunately. :(

Jeff, thank you for crunching those numbers regarding power cables. Sounds like a more viable option than I originally thought it to be. Maybe this is the route to go, combined with running the signal across cat-5 at half-duplex and lower speed (10baseT-HDX). (I may still be missing something??? -- Still need to give this more though and research.)

However, Jeff, you have me extremely curious now with your comment "I can answer the RF questions below if running power is unacceptable." If you would be willing to explain this, I would really appreciate it! It probably opens up options I've erroneously ruled out or don't even know exist.

Thanks in advance.

Sorry, I meant to type "Passive Repeaters".

The peak is not my pers> It does seem a little awkward and non-reproducible. But these are

Ahhh. Didn't notice the word "reflector". I figured we were talking about 103 ft diameter dish or something! I've found comments that "corrugated metal sheets" (with their sine wave-shaped crosscut) work well as reflectors. Makes me wonder if I could somehow reduce the 600 ft distance (by running power and an antenna even further out on my own property), then mount a smaller sheet. Also makes me wonder if the radio/cell towers located 1/3 mile away from the house have passive reflectors already mounted that I could use. (Not likely based on the size issue Jeff brought up. There's also the question of legality.)

Okay, I'm going to need to read this a couple more times to digest it fully, but I get the gist.

If/when you have a chance to tell me about other RF options, please do. In the meantime, this weekend, I'm gonna' go ahead and build a parabolic antenna and see what signals I can find (if any) bouncing down that canyon.

Best regards.

You could do something solar powered on the peak.

Cringely has a writeup about using passive repeaters in the same situation, with no power required.

people question that he actually accomplished this.

Everybody thinks so at first.

It does seem a little awkward and non-reproducible. But these are antennas. Jeff was talking about how large a flat passive reflector would need to be. That's a different thing.

I missed the fact that it is only 600 feet. I was thinking of my own environment, where there's a handy peak, but it's about 1000 feet as the crow flies, across a road, and on someone else's property.

Would it still be on your property?

Lots of problems with "sheets". They are ugly, easily spotted, and catch a lot of wind, so they need to be well mounted. Yagi's present themselves as ideal bird pirtches, a different loading problem.

I think the large telco flat reflectors are, or look like, buildings.

Pointing a directional antenna around randomly to see what signal you get is what some people say made Cringley's setup work, that he wasn't even pointing at his own repeater, that he was actually picking up some naturally echoed signal from a canyon wall in a slightly different direction.

Yech. I finally got around to reading the above article. Cringly used two yagi antennas, back to back. That's very different from a "passive repeater", "passive reflector", or "periscope antenna". The math is simple enough to prove that such a thing will never work. Calcs follow at bottom.

I'm from an engineering background. I practice the cult of calculation before construction. When Cringly supplies reproducible numbers and measurements, I'll believe his claims. However, I am always impressed with his ability to support marginal technology, marginal construction techniques, and dubious practices. As a former hacker, I find his writings inspirational. Well, maybe not quite former hacker.

Reminder: The real trick is that the recommended access point or router can handle a wide range of voltages. It can be done with other routers, but the WRT54G, WAP54G, and such are quite ideal. Incidentally, I forgot to mumble that before I figured it out, I was using DC-to-DC converters to supply regulated 5VDC and sometimes 12VDC down extended power lines, usually up a tower or on an inaccessible rooftop. These worked just fine. One of them is running 3ea WAP11 access points on a rooftop. However, with the WRT54G, it's not necessary to use the DC to DC converter. Also, I had a solar powered access point in a tree, but someone shot a hole in it, so it was removed.

Forcing the access point or router to 10baseT-HDX (half duplex) is the major problem. The easiest way is to use an old 10baseT hub in the circuit, or to use a media converter. Most managed switches will let you set the interface speed and protocol. Now that I think of it, I suspect (not sure) that the WRT54G with DD-WRT firmware will allow you to force the speed on any port. I'll look (when I got time).

That's because the [deleted expletive] telephone would not stop ringing this morning. I just hate it when paying customers interrupt my screwing around. Actually, I was just being lazy/bizzee, as I didn't want to get into the RF aspects if you were just going to do the long power extension cord method.

Ok, but later.

Why Cringly's back to back yagi's wont work.

When you put a passive repeater (back to back yagi's or dish's) in the path, you essentially split the path loss equation in two parts. Let's try a real example using your 600ft numbers and situation.

First the assumptions and guesswork. I'll assume that the remote access point is 1 mile away and has a typical +15dBm access point, 4 dB coax loss, and 8dBi outside omni antenna. The two yagis should have about +12dBi gain each. Your wireless client radio is also a typical +15dbm xmitter with yet a 3rd +12dBi yagi. I'll do the numbers at 5.5Mbits/sec.

Pluging the quesswork into:

Path between remote hot spot and the first yagi antenna. TX power = +15dBm TX coax loss = 4dB (3ft LMR-240 plus a mess of connectors) TX ant gain = 8dB (omni) Distance = 1 mile RX ant gain = +12dBi (yagi) RX coax loss = 1dB (mostly connectors) RX signal = Unknown Grinding the numbers, the RX signal at the yagi's antenna connector will be -74dBm.

Now, we take that -74dBm signal from the first yagi and plug it into the 2nd yagi antenna which is pointed at your client radio. Grinding the numbers: TX power = -74dBm (from first yagi) TX coax loss = 0dB (connector loss take care of in the first yagi) TX ant gain = 12dB (yagi) Distance = 0.114 miles (600ft) RX ant gain = +12dBi (yagi) RX coax loss = 4dB (3ft LMR-240 plus connectos) RX signal = Unknown Grinding the numbers, the RX signal at the client radio receiver will be -139dBm. That *WAY* below the required -85dBm (rx sensitivity) plus another 20dB of fade margin. In other words, the path is 74dB short of working. That's a HUGE amount which can never be (legally) fixed by juggling antenna gains and tx power levels. If I increase all 3 yagi antennas to +24dBi dish antenns, for an additional 36dB system gain, we're still 38dB short of being useable. This isn't gonna work.

I just notice that Cringly said he used a 21dBi Cushcraft dish and cranked up his tx power to +20dBm, but that will help little with a

74dB path gain shortfall. I don't know what Cringly did to make his work, but my calcs show that it can't work.

Corregated sheets don't work as reflectors. The signal bounces all over the place, with little going in the desired direction. It might work if the corregations were less than about 1/10th of a wavelength apart for 2.4Ghz, but that's 1.2cm, which is impractical.

Billboards. I'm talking about a periscope antenna. See: |

Wade calls them "flyswatter" reflectors. Most people call them eyesores. | Ah, found the catalog: | 7MBytes and 118 pages. Lots of nice pictures.

Notice the overkill rigid mounting structure. There's a good reason for to be so beefy. Visualize how far off the beam would be if the structure rotated even a few fractions of a degree. Can you say critical?

Incidentally, the FCC refuses to licence point to point commercial microwave links using periscope antennas because to chronic alignment errors causing interference to other users on the same frequency.

This looks kinda cool. (I haven't tried it yet). |

will do passive repeaters.

Oops, posted the wrong Cringely link earlier. That is interesting, though. If he got his link via a visible neighbor working in July of 2001, why is he hanging Yagi's in trees in 2002?

I just wandered back through the Cringely Archives. He ought to be required to present a scorecard of previous successes and failures after a year.

What about Fusion Lighting killing 802.11b? The web site is gone.