Parabolic Dish Wi Fi Antenna

Does anyone have any experience with such an antenna type as :

http://www.hyperlinktech.com/web/24g...enna_20dbi.php


or are there better antennas to either build or buy ?
Any ideas as to the dimensions of this dish ?

[POSTED TO alt.internet.wireless - REPLY ON USENET PLEASE]

In <(E-Mail Removed) .com> on 9 Nov 2005
12:37:54 -0800, "(E-Mail Removed)" <(E-Mail Removed)> wrote:

>Does anyone have any experience with such an antenna type as :
>
>http://www.hyperlinktech.com/web/24g...enna_20dbi.php
>
> or are there better antennas to either build or buy ?
>...

24dBi for $80:
<http://www.wirelessnetworkproducts.com/index.asp?PageAction=VIEWPROD&ProdID=523>

--
Best regards, HELP FOR CINGULAR GSM & SONY ERICSSON PHONES:
John Navas <http://navasgrp.home.att.net/#Cingular>

(E-Mail Removed) <(E-Mail Removed)> wrote:
> Does anyone have any experience with such an antenna type as :

> http://www.hyperlinktech.com/ ...

Hyperlink has a minimum order of $100, but that doesn't matter, because
this antenna is priced over that.

http://www.fab-corp.com/ has several parabolic antennas for $30-40.

What are you trying to do? 20dBi is a lot of antenna.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5

(E-Mail Removed) wrote:

>(E-Mail Removed) <(E-Mail Removed)> wrote:
>> Does anyone have any experience with such an antenna type as :
>
>> http://www.hyperlinktech.com/ ...
>
>Hyperlink has a minimum order of $100, but that doesn't matter, because
>this antenna is priced over that.
>
>http://www.fab-corp.com/ has several parabolic antennas for $30-40.
>
>What are you trying to do? 20dBi is a lot of antenna.

On a related matter, what sort of range could be achieved by using a
parabolic antenna of say 2ft diameter, at one end, with a conventional
wifi antenna (say inside a laptop) at the other end?

Could 500m be done?

The purpose is to enable running a laptop in a shed about 500m from my
house.

If not, could it be done with such an antenna at both ends? I do have
some Cisco 350 wifi cards with external antenna (MMCX) sockets.

(E-Mail Removed) wrote:

>
> (E-Mail Removed) wrote:
>
>>(E-Mail Removed) <(E-Mail Removed)> wrote:
>>> Does anyone have any experience with such an antenna type as :
>>
>>> http://www.hyperlinktech.com/ ...
>>
>>Hyperlink has a minimum order of $100, but that doesn't matter, because
>>this antenna is priced over that.
>>
>>http://www.fab-corp.com/ has several parabolic antennas for $30-40.
>>
>>What are you trying to do? 20dBi is a lot of antenna.
>
> On a related matter, what sort of range could be achieved by using a
> parabolic antenna of say 2ft diameter, at one end, with a conventional
> wifi antenna (say inside a laptop) at the other end?
>
> Could 500m be done?

With a 14dbi antenna from fab-corp, I could communicate just about exactly
1km to a netgear wireless router without external antenna (at only about
2Mbps, though). I could probably have improved it a bit - the antenna was
hand-held!

I can reliably get the same throughput over 1000' between a Linksys WRT54G
and my Dell laptop - with no external antennas - provided I only have two
windows in the way. However, as soon as I get a stud wall in the way,
reception drops to zero. I suspect 500m to a laptop's internal antenna -
using any size of antenna at the other end - is only going to work in
exceptional circumstances.
--
derek

On Thu, 10 Nov 2005 14:26:46 +0000, (E-Mail Removed)
wrote:

>On a related matter, what sort of range could be achieved by using a
>parabolic antenna of say 2ft diameter, at one end, with a conventional
>wifi antenna (say inside a laptop) at the other end?

I worked out the numbers for a pizza dish illuminated by a USB dongle
in the past. You don't get much gain because most of the RF radiated
by the USB dongle goes in directions that will NOT hit the dish.
http://groups.google.com/group/alt.i...02c84fabb96ef6
There's also a section in that thread that discusses range
calculations. The real problem with using a pizza dish with a
hemispherical radiator (laptop antenna or USB dongle) is that the
antenna gain will be radically different between transmit and receive.
In receive, all of the signal that hits the dish will also hit the
laptop antenna. However in transmit, most of the signal from the
laptop antenna will go to all kinds of useless directions, with very
little hitting the dish. Still, such an arrangement is probably
better than just the laptop antenna and might be worth testing.

>Could 500m be done?

That really depends on what is at the other end. If the access point
is not line of sight, the antenna is crude, and there are
obstructions, forget it.

>The purpose is to enable running a laptop in a shed about 500m from my
>house.
>
>If not, could it be done with such an antenna at both ends? I do have
>some Cisco 350 wifi cards with external antenna (MMCX) sockets.

It would be no problem with external antennas and line of sight. My
guess (I'm too lazy to run the numbers) is about 12dBi of gain in the
antennas at both ends will be sufficient at the slowest 802.11g
speeds. You can always trade range for speed, so I need to know your
minimum acceptable thruput.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann <(E-Mail Removed)> wrote

>It would be no problem with external antennas and line of sight. My
>guess (I'm too lazy to run the numbers) is about 12dBi of gain in the
>antennas at both ends will be sufficient at the slowest 802.11g
>speeds. You can always trade range for speed, so I need to know your
>minimum acceptable thruput.

I've seen 20dbi+ antennae so line of sight seems achievable.
Presumably the drawback of "too much gain" is that it needs accurate
alignment.

On Fri, 11 Nov 2005 08:53:03 +0000, Pete <(E-Mail Removed)
wrote:

>Jeff Liebermann <(E-Mail Removed)> wrote
>
>>It would be no problem with external antennas and line of sight. My
>>guess (I'm too lazy to run the numbers) is about 12dBi of gain in the
>>antennas at both ends will be sufficient at the slowest 802.11g
>>speeds. You can always trade range for speed, so I need to know your
>>minimum acceptable thruput.

>I've seen 20dbi+ antennae so line of sight seems achievable.
>Presumably the drawback of "too much gain" is that it needs accurate
>alignment.

The common "barbeque grill" Pacific Wireless dish antennas come in
15dBi, 19dBi, and 24dBi models with prices from $30-$70. At those
prices, it's not worth building one.

The gain of the antenna has nothing to do with line of sight. If you
don't have line of sight, no amount of gain will "drill through" the
obstruction. In my opinion, line of sight is far more important than
antenna gain. However, if the obstruction is porous, such as trees
and bushes, antenna gain might be able to penetrate the foliage.

What really happens with antenna gain is that the "fade margin"
increases with more gain. This means that the system will tolerate
more reflections, multipath, obstructions, deterioration, water in the
coax, and interference. 20dB fade margin is a starting number. Larger
is better.

Increased directional antenna gain also implies a much narrower
antenna -3dB beamwidth. That will keep out any co-channel
interference but as you mention, does make antenna alignment an
adventure. At 500m it should not be a problem. However at longer
distances, alignment becomes critical with the big 24dBi dishes. At
5.6GHz with a 32dBi dish, it's really touchy.

Another problem with "too much gain" is overload. The dynamic range
of the typical access point and client radio receivers is not very
good. My guess(tm) is any signal over -20dBm will cause a problem.
One has to be fairly close to get such a strong signal, but it can be
done easily with two high gain antennas. The result is "envelope
distortion" which mutilates the AM component of the 802.11b/g signal
and causes the error rate to increase. This is why you don't want two
24dBi antennas pointed at each other in close proximity. Running the
numbers:
TX power: 17dBi
TX coax loss: 3dB
TX Ant gain: 24dBi
Path loss: Unknown
RX Ant gain: 24dBi
RX coax loss: 3dB
Signal at receiver: -20dBm
Since bankrupt Proxim bought Terrabeam which bought YDI, my favorite
simple online RF path loss calculator is now history, so let's do this
one mostly by hand.
17 -3 +24 +24 -3 = +59dBm
Therefore, the path loss to get -20dBm at the receiver is:
59 - (-20) = 79dB
Plugging by trial and error to get 79dB into:
http://www.firstmilewireless.com/calc_pathloss.html
yields a distance of 0.06 miles or 97 meters. Therefore, any such
arrangement of two big dish antennas closer than 97 meters is going to
cause overload problems at the receiver.

Note that the -20dBm overload point is my guess and will vary
substantially by receiver design and chipset.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558