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Pelethora of Questions

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Anonymous
December 18, 2004 5:09:09 PM

Archived from groups: alt.internet.wireless (More info?)

Newbie Warning: This post will rable, so get out now if newbies annoy you.

OK, I live in an area without broadband access, so I decided to look at
getting a long-range wi-fi connection to some houses nearby that could
get broadband (definately less than 7ks).

I've done a lot of research in the past two days before hitting this group:
About.com
http://bloodnok.coders.net.nyud.net:8090/sub/dish/
http://www.binarywolf.com/249/pringles.htm
http://www.usbwifi.orcon.net.nz/
Google.com ;-)

It seems that best performance gains come from highly-directional
parabolic dish antenna, is this correct? Also, how "strict" is the
directional element? The sites didn't say. At a long range, can I be off
by a few degrees? Any tips for getting it right are also useful. I don't
need the construct the dish to any particular specifications, do I? Not
like having to calucate 3/4 wavelength were I to use a pringles-can design.

My main question, though, is about joining my home network to the
network at the remote house.

Can I just have a computer at my house (connecting to my network) in
ad-hoc mode with a router at the remote house, which is connected by
crossover cable to that person's computer?

Or must I have two APs (or an AP at my house bridging to my network and
a router at the remote house also connected to the 'net and thier
computer)? If I used an AP, am I correct in thinking that I can connect
it directly via ethernet to my switch (and therefore need no wireless
cards at all)?

Someone told me that external antenna can only be attached to APs, and
also it seems that USB cables have a maximum length of about 15 - which
is too short for me (and I'm not buying an extension that converts to
ethernet and back)... This would seem to suggest a network structure like:

192.168.x.x

KEY: | -- : Ethernet cable
~ ~ ~ : Wireless

0.2 INTERNET
| |
| |
SWITCH----AP ~ ~ ~ ~ ~ WIRELESS ROUTER
| | |
| 0.3 |
0.2 0.1 Their Computer

Or the right-side of the diagram being alternately:

INTERNET
|
~ ~ ~ AP----PC ROUTER 0.1
|
1.1 Thier Computer

Therefore the wireless stuff is but a bridge, with all the connections
to computers themselves handled by ethernet.

Apologies again for the long post, but this stuff wasn't obvious - even
from the About.com articles, which were very helpful. Also, it helps to
have some people who know what they're doing directly look at the case.

Thanks for any replies :-)

More about : pelethora questions

Anonymous
December 18, 2004 5:09:10 PM

Archived from groups: alt.internet.wireless (More info?)

Will Gittoes <AskMeForIt@nospam.org.invalid> wrote:
> Newbie Warning: This post will rable, so get out now if newbies annoy you.

> OK, I live in an area without broadband access, so I decided to look at
> getting a long-range wi-fi connection to some houses nearby that could
> get broadband (definately less than 7ks).

You should have searched this group ;-)
http://groups-beta.google.com/group/alt.internet.wirele...

You might have found references to someone's one mile link through the
trees, although that one escapes me at the moment.
But there are these two:

David Taylor's is a good story and good writeup.
http://www.nodomainname.co.uk/Equation/equation_broadba...

Craig's is a long link, with good mapping detail.
http://www.craig-bartell.com/

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
Anonymous
December 19, 2004 9:13:11 AM

Archived from groups: alt.internet.wireless (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
> It's not that difficult. The problem is that many highly directional
> antennas suffer from boresight mis-alignment. The RF peak does not
> coincide with the mechanical boresight axis. If you build your dish
> with a center tube support, you'll have a built in boresight for
> aiming. If not, then clamp a cheap telescopic sight onto a right
> angle carpenters square, and place the square across the width of the

You've said this before, and I've missed the methodology.
Are you saying that the RF pattern isn't aligned where one would think it
is? I thought I was following along, that the RF isn't squarely off the
visual bore of the dish, until you suggested putting a carpenters square on
it. If the RF isn't squarely aligned, why do you want a visual aid that is
squarely aligned?

I thought you were referring to something like a DirecTV dish, which has a
feed that is off center.



> Incidentally, the gain of the typical coffee can antenna is about 8dBi
> at best. That's not enough gain for a reliable 7km link.

http://members.cruzio.com/~jeffl/pics/antennas/coffee24...

My USB-dongle sees a 3dB received signal increase by placing a flat cookie
sheet about an inch behind the dongle. About 9dB with a double cofffee
can. I don't think I'll be trying for a 7km link. I only wanted about
two city blocks to hit a "UPS Store" hotspot.

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
Anonymous
December 19, 2004 9:13:12 AM

Archived from groups: alt.internet.wireless (More info?)

On Sun, 19 Dec 2004 06:13:11 +0000 (UTC),
dold@XReXXPelet.usenet.us.com wrote:

>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
>> It's not that difficult. The problem is that many highly directional
>> antennas suffer from boresight mis-alignment. The RF peak does not
>> coincide with the mechanical boresight axis. If you build your dish
>> with a center tube support, you'll have a built in boresight for
>> aiming. If not, then clamp a cheap telescopic sight onto a right
>> angle carpenters square, and place the square across the width of the

>You've said this before, and I've missed the methodology.
>Are you saying that the RF pattern isn't aligned where one would think it
>is?

Yep. It's a problem with both high gain dishes and panels. When the
beamwidth is <10 degrees, mecahnical rigidity and asymmetrical feed
patterns (due to radiating coax) becomes a problem. The error isn't
much, usually <2 degrees, but it's noticeable.

For example, I added the horizontal pattern of Trevor Marshall's
coffee can antenna model to my web pile at:
http://www.LearnByDestroying.com/pics/antennas/coffee24...
The vertical radiation pattern is symmetrical and aligned with the
boresight. The horizontal isn't even close. If such a can antenna
was used to illuminate a parabolic dish, my guess(tm) is that the RF
pattern would be misaligned with the boresight by about 1.5 degrees.

A similar problem is caused by dipole dish feeds without baluns. A
balun is effectively a tranformer (usually 1:1 or 4:1) that deals with
a coax to balanced line transition. The basic idea is to prevent the
coax cable from becoming part of the antenna and screwing up the
pattern. Here's an example of the right way to do it:
http://martybugs.net/wireless/conifermods2.cgi#dipole
Note the 30.5mm (1/4 wave) copper pipe with the slots. That's the
balun.

Here's how to do it wrong:
http://www.ashtec.dyndns.org/ashtec/mods/index.html
Notice the out of focus photo showing the dipole, without a balun.
That's going to have lower gain, higher vswr, and a skewed pattern.

>I thought I was following along, that the RF isn't squarely off the
>visual bore of the dish, until you suggested putting a carpenters square on
>it. If the RF isn't squarely aligned, why do you want a visual aid that is
>squarely aligned?

Just getting it close. You'll find that it's amazingly difficult to
align a dish antenna to within a few degrees without some kind of
optical alignment aids. It's really bad on a tower where you can't
back off away from the antenna to take an optical sighting. The
carpenters square gets you in the ballpark. The rest is tweaking (and
guesswork).

>I thought you were referring to something like a DirecTV dish, which has a
>feed that is off center.

Nope. Those are even more difficult to align. A carpenters square
will only work for horizontal alignment. One of my dumber ideas as
shown in:
http://www.LearnByDestroying.com/pics/wireless/slides/p...
turned into a real challenge to align. So, I cheated. I setup a
nearby 2.4Ghz X10 tv link, jiggled the antenna for maximum, attached a
rifle scope to the edge, and aligned it with the X10 xmitter. That
determined the exact RF peak direction. Then, I pointed it at the
distant mountaintop. It worked the first time.

There are other tricks. One of my favorite only works with Pacfic
Wireless dishes. They use an extension tube for the 24dBi dish. By
removing the locking bolt from the extension tube, it can be moved
inward about 2 inches. When moved about an inch, the antenna is
defocused into a much wider pattern (and lower gain). The much wider
pattern makes it easier to aim.

With higher gain antennas, there are even weirder antenna pointing
problems. A center mounted feed presents a "shadow" on the dish, and
therefore has reduced gain along the boresight. The result is a dip
in gain along the boresight with the peak gain forming a donut around
the boresight line. Aiming one these abominations is no fun. The
good news is that you probably won't see this with a dipole or yagi
fed 2.4Ghz 24dBi dish. You will see it with a much larger, cantenna
fed dish.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
!