Pelethora of Questions

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 :-)

Will Gittoes <(E-Mail Removed)> 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/...ernet.wireless

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/Equati..._broadband.htm

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

On Sat, 18 Dec 2004 14:09:09 +1300, Will Gittoes
<(E-Mail Removed)> wrote:

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

I think you mean ramble, not rable. Newbies don't annoy me. I like
to take the easy questions and let everyone else try to answer the
tough ones.

>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).

Is that 7km?

>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 ;-)

Ok, you got your feet wet. Next step is to jump into the swamp with
both feet. Keep reading.

>It seems that best performance gains come from highly-directional
>parabolic dish antenna, is this correct?

Basically correct. The largest practical and commonly available dish
antenna has 24dBi gain. It's about 1 meter across and looks like a
mangled barbeque grill.
http://www.fab-corp.com/B1.htm

>Also, how "strict" is the
>directional element? The sites didn't say. At a long range, can I be off
>by a few degrees?

Looks at the specification sheet for a 24dBi dish. You'll see
something like "3dB beamwidth". For a 24dBi dish, that's usually
about 7 degrees. That means that most of your power is within 3.5
degrees of the center line. I theory, you can be +/- 3.5 degrees off
center and still have a useable link. Beyond 3.5 degrees, the signal
falls off rapidly. As a general rule of thumb, you should be accurate
to at least within half of the -3dB beamwidth. That's about the same
accuracy as required for the typical 0.5 meter DBS pizza dish.

>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.

I would advise against building your own dish, especially if you
haven't done anything like this before, and since you don't have any
proper RF test equipment. Pringles and coffee can antennas are fairly
non-critical. Dishes are tricky. 24dBi dishes are about $52/ea.

>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?

Ad-hoc mode does NOT talk or use a wireless router. Your best bet it
to buy a pair of transparent bridge radios (i.e. WAP54G, DWL-900AP+,
etc) which will allow multiple computers at each end without a router.
However, if this is going to be a point to multipoint link, then use
an access point (WRT54G) at the end with the broadband, and a client
radio (WAP54G) at your end.

>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)?

Access points do not talk to other access points unless you either use
alternative (hacked) firmware, or use WDS (wireless distribution
something). You can connect your access point to a switch or hub.

>Someone told me that external antenna can only be attached to APs,

Many access points have external antenna connectors, usually R-SMA or
R-TNC. Most client radios have either built in antennas (PCMCIA, USB,
etc), that are more difficult to connect to an external antenna. Some
have connectors (Proxim/Orinoco).

>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)

16ft maximum. However, repeaters are available that will go hundreds
of feet. It isn't the data link that craps out. It's the 5VDC
regulated power that runs the radio that dies from excessive copper
loss.

>... 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.

I don't understand what you're trying to do with the above mess.
A wireless transparent bridge is (duh!) transparent. That means it
will pass anything that looks like an ethernet packet that's destined
to cross the bridge. Bridges don't know anything about IP addresses,
so your IP address layout is useless. With a wireless bridge, it's
all one big network using the same class C IP block on both sides of
the link.

>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 :-)

Try reading white papers and articles at:
http://www.tomsnetworking.com
and the product reviews at:
http://www.practicallynetworked.com


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# (E-Mail Removed)
# (E-Mail Removed) AE6KS

Jeff Liebermann wrote:
> On Sat, 18 Dec 2004 14:09:09 +1300, Will Gittoes
> <(E-Mail Removed)> wrote:
>
>
>>Newbie Warning: This post will rable, so get out now if newbies annoy you.
>
>
> I think you mean ramble, not rable. Newbies don't annoy me. I like
> to take the easy questions and let everyone else try to answer the
> tough ones.

Haha, I do that myself on all the Linux groups :-)

>
>
>>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).
>
>
> Is that 7km?

Yep.

>
>
>>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 ;-)
>
>
> Ok, you got your feet wet. Next step is to jump into the swamp with
> both feet. Keep reading.
>
>
>>It seems that best performance gains come from highly-directional
>>parabolic dish antenna, is this correct?
>
>
> Basically correct. The largest practical and commonly available dish
> antenna has 24dBi gain. It's about 1 meter across and looks like a
> mangled barbeque grill.
> http://www.fab-corp.com/B1.htm

Heh, I plan to use lots of fine mesh for mine.

>
>
>>Also, how "strict" is the
>>directional element? The sites didn't say. At a long range, can I be off
>>by a few degrees?
>
>
> Looks at the specification sheet for a 24dBi dish. You'll see
> something like "3dB beamwidth". For a 24dBi dish, that's usually
> about 7 degrees. That means that most of your power is within 3.5
> degrees of the center line. I theory, you can be +/- 3.5 degrees off
> center and still have a useable link. Beyond 3.5 degrees, the signal
> falls off rapidly. As a general rule of thumb, you should be accurate
> to at least within half of the -3dB beamwidth. That's about the same
> accuracy as required for the typical 0.5 meter DBS pizza dish.

Hmmm... methinks this will take a few hours of aiming...
Do you think I could have an AP at one end and a big dish at the
other... and just aim the dish at the AP... would that cover 7km?

I plan to build quite a massive dish, I've got some sturdy trees to
string it up between.

>
>
>>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.
>
>
> I would advise against building your own dish, especially if you
> haven't done anything like this before, and since you don't have any
> proper RF test equipment. Pringles and coffee can antennas are fairly
> non-critical. Dishes are tricky. 24dBi dishes are about $52/ea.

Aahhh, I do plan to build one myself. I'm a good mathematician (but a
poor speller). Parabola: Ax^2 + Bx + c I can handle that. Fine mesh
wire, deeper parabola for better transmission, larger dish for better
reception.

I'll use a relatively deep dish like 0.7*(x^2), and have that equaltion
to create 16 "spokes". Then, at regular intervals along the spokes,
there will be a "rim", which can have it's cirumference calculated by:

r=x
circumference = 2*pi*r

Easy peasy.

>
>
>>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?
>
>
> Ad-hoc mode does NOT talk or use a wireless router. Your best bet it
> to buy a pair of transparent bridge radios (i.e. WAP54G, DWL-900AP+,
> etc) which will allow multiple computers at each end without a router.
> However, if this is going to be a point to multipoint link, then use
> an access point (WRT54G) at the end with the broadband, and a client
> radio (WAP54G) at your end.
>
>

OK, I've been reading more, and it seems that most people using LONG
links buy the little USB "nub", and place that at the focal point of the
dish. This would suggest to me either ad-hoc point-to-point, or an AP at
one end, and a truely gigantic dish at the other.

If I had two computers conencted via ad-hoc, am I correct in thinking
that the computers connected TO the computers on the wireless link will
NOT have to masquerade. This is hard to explain.

Can the computer at each end of the ad-hoc link be connected to other
computers via a regular switch, and have them all on the same network;
sort of like a daisy-chain? Also, when I said router; I didn't mean a
wireless one - just another PC on the network.

>
>
>>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)
>
>
> 16ft maximum. However, repeaters are available that will go hundreds
> of feet. It isn't the data link that craps out. It's the 5VDC
> regulated power that runs the radio that dies from excessive copper
> loss.

Yes... but those USB > Ethernet > USB connectors (150m ethernet max
length is good) are very expensive.

>
>
>>... This would seem to suggest a network structure like:
>>
>>
>>Therefore the wireless stuff is but a bridge, with all the connections
>>to computers themselves handled by ethernet.
>
>
> I don't understand what you're trying to do with the above mess.
> A wireless transparent bridge is (duh!) transparent. That means it
> will pass anything that looks like an ethernet packet that's destined
> to cross the bridge. Bridges don't know anything about IP addresses,
> so your IP address layout is useless. With a wireless bridge, it's
> all one big network using the same class C IP block on both sides of
> the link.

Yes, this is what I want! Everyone to be in the same network - but I was
unsure of whether network packets would be forewarded through the
wireless link or not; and whether chaining the computers together would
mess this up.

>
>
>>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 :-)
>
>
> Try reading white papers and articles at:
> http://www.tomsnetworking.com
> and the product reviews at:
> http://www.practicallynetworked.com
>
>

Cheers for all your help!

On Sun, 19 Dec 2004 14:43:23 +1300, Will Gittoes
<(E-Mail Removed)> wrote:

>Heh, I plan to use lots of fine mesh for mine.

"Learn by Destroying(tm)"
http://www.eurasianet.org/department...abuldishes.jpg
The original photos were dishes made from flattened paint and soda
cans.

>Hmmm... methinks this will take a few hours of aiming...

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
dish. I've also used CCD TV cameras, inclineometers, bubble levels,
lasers, and brute force. At 7km, a +/-1 degree error is:
tan(1) * 7000m = +/-122 meters
so you have some leeway.

>Do you think I could have an AP at one end and a big dish at the
>other... and just aim the dish at the AP... would that cover 7km?

Nope. Let's play with the numbers.

You have a 24dBi dish at one end, and a 2dBi piece of junk on the AP
at the other. The typical access point belches +15dBm. The range is
7km or 4.35 miles. You'll need an absolute minimum of 10dB fade
margin for anything to work. 20dB would be a good target value. I
don't have a clue as to how much coax cable you're gonna use so I'll
assume that you place the radio on the roof along with the dish at one
end, and directly to the access point (in a window) on the other end.

Using receiver sensitivity numbers from a DI-624 (close enough).
* 54Mbps OFDM, 10% PER, -68dBm)
* 48Mbps OFDM, 10% PER, -68dBm)
* 36Mbps OFDM, 10% PER, -75dBm)
* 24Mbps OFDM, 10% PER, -79dBm)
* 18Mbps OFDM, 10% PER, -82dBm)
* 12Mbps OFDM, 10% PER, -84dBm)
* 11Mbps CCK, 8% PER, -82dBm)
* 9Mbps OFDM, 10% PER, -87dBm)
* 6Mbps OFDM, 10% PER, -88dBm)
* 5.5Mbps CCK, 8% PER, -85dBm)
* 2Mbps QPSK, 8% PER, -86dBm)
* 1Mbps BPSK, 8% PER, -89dBm)
I can now arbitrarily decide that you'll want to run 12Mbits/sec which
will yield a thruput of about 6Mbits/sec. That gives a receive
sensitivity of -84dBm.
Distance = 4.35 miles
TX power = +15dBm
RX sens = -84dBm (at 12Mbits/sec OFDM)
TX ant gain = 24dBi
RX ant gain = 2dBi
TX coax loss = 3dB
RX coax loss = 0dB
Plugging into:
http://www.ydi.com/calculation/som.php
yields a 5dB fade margin. You'll barely get a connection, but the
speed and reliability will suck. The slightest bit of interference
will kill the connection. You'll need about 20dB more antenna gain to
make this work. That means a dish antenna at both ends.

>I plan to build quite a massive dish, I've got some sturdy trees to
>string it up between.

Are you planning to do this legally? With too big a dish, you could
go over the FCC power limit. It's fairly hard to do that, but it can
be done.

Big dishes have even narrower beamwidth than the typical 24dBi dish.
however, that's not the major construction problem. It's building a
suitable feed that properly illuminates the dish. See:
http://www.qsl.net/n1bwt/contents.htm

>Aahhh, I do plan to build one myself. I'm a good mathematician (but a
>poor speller). Parabola: Ax^2 + Bx + c I can handle that. Fine mesh
>wire, deeper parabola for better transmission, larger dish for better
>reception.
>
>I'll use a relatively deep dish like 0.7*(x^2), and have that equaltion
>to create 16 "spokes". Then, at regular intervals along the spokes,
>there will be a "rim", which can have it's cirumference calculated by:
>
>r=x
>circumference = 2*pi*r
>
>Easy peasy.

Optimism, the first symptom of impending disaster. The "depth" of a
dish is measured by the f/D (focal length / Diameter) ratio. A deep
dish (f/D < 0.35) requires a scalar ring feed for proper illumination.
It also doesn't scale well as reflection from the dish near the edge,
doesn't contribute as much gain as reflections from near the center
feed.

On the other foot, relatively flat shallow dishes are more efficient
and require a less complex feed, but have rediculously long center
boom. If you don't mind a long ugly boom, that's probably the way to
go. Suggestion: Figure out the characteristics of your feed and size
the dish to fit, not the other way around.

I can supply URL's for dish construction articles, but dinner comes
first.

>OK, I've been reading more, and it seems that most people using LONG
>links buy the little USB "nub", and place that at the focal point of the
>dish. This would suggest to me either ad-hoc point-to-point, or an AP at
>one end, and a truely gigantic dish at the other.

Nope. Those are the people that live near a free hot spot and want to
get free broadband internet from the hot spot. The problem with this
arrangement for a point to point link is that you'll pickup far too
much junk and reflections at the omni antenna access point. Antenna
gain isn't just for getting a good signal. It's also for excluding
interference from the sides and back of the antenna.

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

>If I had two computers conencted via ad-hoc, am I correct in thinking
>that the computers connected TO the computers on the wireless link will
>NOT have to masquerade. This is hard to explain.

IPMasq is NAT. Ad-hoc will deliver exactly one MAC address. So, if
you have more than one computah on your LAN, you'll need to use a
router and NAT at your end to shovel them through the one IP address.
If you built a transparent bridge, you could pass multiple MAC
addresses and live without the router and NAT.

>Can the computer at each end of the ad-hoc link be connected to other
>computers via a regular switch, and have them all on the same network;
>sort of like a daisy-chain?

No. One MAC address passed allow only one computah to go through the
link.

>Also, when I said router; I didn't mean a
>wireless one - just another PC on the network.

A wireless router is a wireless access point (bridge) and a router in
one box.

>> With a wireless bridge, it's
>> all one big network using the same class C IP block on both sides of
>> the link.
>
>Yes, this is what I want! Everyone to be in the same network - but I was
>unsure of whether network packets would be forewarded through the
>wireless link or not; and whether chaining the computers together would
>mess this up.

In that case, you'll need two boxes that can play transparent bridge.
These are also called workgroup bridges or game adapters. The game
adapters are somewhat of a crap shoot as some will pass multiple MAC
addresses, while others will pass only one. It's difficult to tell
from the data sheets how many MAC addresses will be passed. Good
transparent bridges are Linksys WAP54G and DLink DWL-900AP+. I'm not
thrilled with the DLink DWL-2100AP. There are others, but make sure
you're buying a wireless bridge, not an access point or wireless
router. The cheapo wireless bridges will do 32 MAC addresses (30
machines). The newer boxes will do up to 256. The better boxes
(Proxim, Alvarion) will do 2048 addresses.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

Jeff Liebermann <(E-Mail Removed)> 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/pic...as/coffee2400/

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

On Sun, 19 Dec 2004 06:13:11 +0000 (UTC),
(E-Mail Removed) wrote:

>Jeff Liebermann <(E-Mail Removed)> 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/pic...400/index.html
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/pic...primestar.html
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 (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558