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LOCATION: NARRE WARREN NORTH
I have a pretty good take off to the South towards Narre Warren and
West to Endeavour Hills.
Using a DWL-650 card connected to a 18dBi ex Galaxy antenna on an
antenna rotator. Note that the antenna polarisation is vertical.
Is there anyone else active in the area?
GMI Antenna [1]
DWL-650 CARD
These are my mods to the DWL-650, I used a short length of RG188 coax
from
card as it is very flexible and small in diameter (also teflon, so
wont melt).
An SMA connector is used on the tail. These are heaps more rugged
than the
MMCX connectors.
Dlink mods [2]
I was a bit worried about the strain that the coax tail placed on the
card, so I made a little strain relief from plastic and bolted the SMA
socket on the tail to the plastic. The idea behind using plastic for
the SMA socket mount was to protect the card from damage. Should the
plastic strain relief become caught on something solid, it will break,
rather than break the PCMCIA card protrusion.
Card Strain Relief [3]
There are some details on the web showing how to add a tail to the
DWL-650 and also stating that it does not matter which diversity
antenna connection is re routed to the tail. My experience shows it
does matter. When I re routed the antenna capacitor as shown in the
earlier image, I found that although the card received signals well
through the tail, I could not see any RF power on a power meter
through the tail.
When I made an RF sniffer loop and placed it over the internal
antenna, I noted RF only from the internal antenna.
To generate a constant RF transmission WLAN Expert was used in
Antenna Test mode. Of course the RF transmit signal is bursty, but at
least it is regular enough to measure.
The coax tail was then re connected to the other internal antenna and
the previous connection restored to the other internal antenna.
This time RF output was measured on the coax tail. The card was also
receiving fine through the tail.
My conclusion is that although both internal antenna are used for
diversity receive, only one antenna does the transmitting. This in my
case is the opposite antenna connection as shown in the previous
image.
It is possible that the card behaves differently in other modes, but
I have only detected RF transmission from the one internal antenna so
far.
BIQUAD ANTENNA
Made a biquad antenna and covered it with radome made from a hobby
box. It is based on the design described in
http://www.martybugs.net/wireless/biquad/
The antenna matches and performs very well.
Here are some photos:
Biquad pic 1 [4]
Biquad pic 2 [5]
Biquad pic 3 [6]
HELICAL ANTENNA
Put together a 12 turn helical antenna based on Remco den Besten's
design from
http://helix.remco.tk/ and did some tests on air. So far it doesn't
perform so well taking in to account that its circular polarisation
will be down 3dB from a linearly polarised antenna. Will have to check
it out on the network analyser.
Helical pic [7]
Redesigned the match on the helical and now the thing seems to work
as expected. Not too sure on the basis for the design for the old
match. The match I used is based on a transmission line fabricated
from a curved strip of copper foil running almost parallel to the
reflector. The theory and implementation is described in the ARRL
handbook.
Helical match [8]
AEROSOL QUESTIONS
Using Aerosol for sniffing packets but have a few questions on it as
I don't have any documentation. Does anyone have experience with this
program?
The readme says to set the SSID to nothing for it to work properly,
but when
I do this the PC slows to a crawl and eventually freezes.
20030428: Sorted it out. Turns out that if you set the SSID to blank
while in adhoc things go crazy. A blank SSID while in infrastructure
mode is OK. Also WLAN Expert utility leaves the driver in a funny
state after it exits. Going to the DLink utility and pressing rescan
seems to recover it.
Also driver DLink V1.32 only works, the latest from web site doesn't
(on my Toshiba 410CS anyway).
When using V1.32, must modify the netcw10.inf file after driver
installation by adding code so that it works with standard PCMCIA slot
not Cardbus slot as driver assumes. Ancient Toshiba 410CS does not
have Cardbus slot. Is nothing simple?
Aerosol [9]
POLARISATION STANDARDISATION
Is there a standard for polarisation? Have seen some wireless users
with Conifer antennas vertically polarised and some horizontally.
There is a huge penality for cross polarisation (up to 20dB). The
omnis such as vertically mounted waveguides are horizontal
polarisation while coaxial co-linear omnis are vertically polarised.
NODES IN RANGE
Now can connect to NodeGXT [10], over a 7.3km path. Connection is
only 1-2Mbit/s, but it's there! Some optimisation of the setup at
either end should improve the connection.
Using 24dBi Galaxy antenna at either end.
Have managed to connect to NodeACD [11] after a polarisation switch
to vertical and a temporary relocation of the antenna. The trunk of a
big cypress tree was in the way. Should be enough signal to use after
some optimisation of feeder and antenna.
[12] may be LOS. Here is a photo in the direction of GSJ with 30x
optical zoom at a distance of 5km.
View to GSJ [13]
Here are some path profiles done with Pathloss for the two nodes.
Note that the terrain data used by the package has a resolution of
about 200 metres so it's probably not that accurate for the 1km path.
Path to ACD [14]
Path to GSJ [15]
2003-07-13: Link to NodeACD [16] has now been stable for 24hrs with
-78dBm signals at NodeGMI [17]. Reported link speed of between 5.5 and
11Mbit/sec.
2003-11-29: SVEC AP MOUNTED ON MAST
To reduce coax losses the SVEC AP is now mounted on the mast behind
the antenna. This results in much more signal on the link between GMI
and GXT.
The box is a Jaycar weatherproof enclosure with dimensions about
165x220x55mm.
Power over Ethernet supplies 12VDC to the enclosure where it is
converted to 5VDC by a switchmode DC converter. A switching convertor
was chosen so as to minimise heat build up within the enclosure. Has
been running for a couple of days with only slight temp increase
inside although it will need some sort of sun screen to shade direct
sunlight from the enclosure in the warmer months.
See picture:
SVEC in box [18]
Well it was 33 degrees today and the thermometer probe inside the box
only reported a max of 40 degrees. Guess it will survive the summer
then.
SVEC Temperature [19]
2003-12-12: NEW DISH FEED FOR PARABOLIC
This is an experimental feed made from:
- half inch copper plumbing pipe
- brass tube from hobby shop
- RG214 coax
- disk of brass sheet for reflector
Seems to work OK so far, will compare it with Hills dipole feed.
Dipole dish feed 1 [20]
Dipole dish feed 2 [21]
Dipole dish feed 2 [22]
:
2004-02-22 LINK TO GXQ
Set up the link to GXQ today over 6.2km path. This one worked with no
problems.
This is another point to point link using the above experimental feed
on the conifer dish (18dBi).
Signals can be received at GXQ on a biquad, so the 26dBi at GXQ
should have heaps of link margin.
The point to point link connecting GMI to GXT is using a 26dBi
conifer at the other end of the house on a short mast. This link is
now very reliable.
===========================================================================
COMMENTS:
Links:
------
[1] http://web.aanet.com.au/glenns/images/conifer_rotator.jpg
[2] http://web.aanet.com.au/glenns/images/dlink_mod1.jpg
[3] http://web.aanet.com.au/glenns/images/dlink_sma2.jpg
[4] http://web.aanet.com.au/glenns/images/biquad1.jpg
[5] http://web.aanet.com.au/glenns/images/biquad2.jpg
[6] http://web.aanet.com.au/glenns/images/biquad3.jpg
[7] http://web.aanet.com.au/glenns/images/helix.jpg
[8] http://web.aanet.com.au/glenns/images/new_helix_match.jpg
[9] http://www.stolenshoes.net/sniph/index.html
[10] http://www.melbournewireless.org.au/?NodeGXT
[11] http://www.melbournewireless.org.au/?NodeACD
[12] http://www.melbournewireless.org.au/?NodeGSJ
[13] http://web.aanet.com.au/glenns/images/NodeGSJ_from_GMI.jpg
[14] http://web.aanet.com.au/glenns/images/path_acd_gmi.jpg
[15] http://web.aanet.com.au/glenns/images/path_gsj_gmi.jpg
[16] http://www.melbournewireless.org.au/?NodeACD
[17] http://www.melbournewireless.org.au/?NodeGMI
[18] http://web.aanet.com.au/glenns/images/svecAP_in_a_box.jpg
[19] http://web.aanet.com.au/glenns/images/ap2.jpg
[20] http://web.aanet.com.au/glenns/images/feed_1.jpg
[21] http://web.aanet.com.au/glenns/images/feed_2.jpg
[22] http://web.aanet.com.au/glenns/images/feed_3.jpg
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