Wi-Fi antenna postscrip

[Bruce]

I ended up building two wi-fi parabolic antenna. the first a 300 mm
screen-wire dipper (used for frying bananas) measured 300 mm in
diameter and about 90 mm deep. Later built a second dish using a 430
mm aluminum "wok" about 100 mm deep.

The first antenna gave a better signal then the adapter but the second
antenna gave, using the instruments available to me, approximately 3
times the signal that the bare wi-fi "adapter" had.

As I previously mentioned I do not have a signal strength meter and
used the standard Linux utility "iwconfig" to produce some sort of
data. It gave a reading of 6 for signal strength using the bare
adapter and as high as 23 with the wok I can only assume that whatever
the value of the increments that the ratio is accurate.

As luck would have it, I found an abandoned TV "cable" antenna - as
used here "cable" is received on a 3 foot dia. parabolic antenna and I
will probably try that at some later date.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

 

[Bruce in alaska]

As I previously mentioned I do not have a signal strength meter and
used the standard Linux utility "iwconfig" to produce some sort of
data. It gave a reading of 6 for signal strength using the bare
adapter and as high as 23 with the wok I can only assume that whatever
the value of the increments that the ratio is accurate.

As luck would have it, I found an abandoned TV "cable" antenna - as
used here "cable" is received on a 3 foot dia. parabolic antenna and I
will probably try that at some later date.

My question is what makes you think that these two "dishes" are
Parabolas, and not just dish shaped? I would bet that the TV dish will
work significantly better than any dish shaped reflector, simply because
it will have the correct mathematical shape, and the Focal Point will be
defined properly by the designers.

 

[Bruce]

My question is what makes you think that these two "dishes" are
Parabolas, and not just dish shaped? I would bet that the TV dish will
work significantly better than any dish shaped reflector, simply because
it will have the correct mathematical shape, and the Focal Point will be
defined properly by the designers.

I don't particularly think that the cooking dishes have a correct
parabolic shape. I was attempting to solve a problem with what I could
get my hands on. The discovery of the "cable TV dish" came shortly
after I had completed the 17" wok.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

 

[Steve Lusardi]

As I stated Bruce, the TV antenna is a good plan. It will be a true parabola and the gain over what you have will be significant.
Don't forget about the 30 degree included angle that is built in. You will have to move the detector up to the center for your
application.
Steve

 

[Bruce]

As I stated Bruce, the TV antenna is a good plan. It will be a true parabola and the gain over what you have will be significant.
Don't forget about the 30 degree included angle that is built in. You will have to move the detector up to the center for your
application.
Steve

No worry about misalignment a there is no "horn" on it. Just a dish

It is currently being used as a "roof" for a well pump and I have some
20 ltr. pails that, with a notch cut in one side to clear the piping
will work even better so I reckon a trade can be made... once I and
them get back to Phuket.
Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

 

[Larry]

I ended up building two wi-fi parabolic antenna. the first a 300 mm
screen-wire dipper (used for frying bananas) measured 300 mm in
diameter and about 90 mm deep. Later built a second dish using a 430
mm aluminum "wok" about 100 mm deep.

The first antenna gave a better signal then the adapter but the second
antenna gave, using the instruments available to me, approximately 3
times the signal that the bare wi-fi "adapter" had.

As I previously mentioned I do not have a signal strength meter and
used the standard Linux utility "iwconfig" to produce some sort of
data. It gave a reading of 6 for signal strength using the bare
adapter and as high as 23 with the wok I can only assume that whatever
the value of the increments that the ratio is accurate.

As luck would have it, I found an abandoned TV "cable" antenna - as
used here "cable" is received on a 3 foot dia. parabolic antenna and I
will probably try that at some later date.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

http://www.turnpoint.net/wireless/has.html

http://www.oreillynet.com/cs/weblog/view/wlg/448

http://binarywolf.com/249/pringles_cantenna.htm

http://www.netscum.com/~clapp/wireless.html

http://www.seattlewireless.net/PringlesCantenna

We get about 1.5 miles range from my 200mw hotspot with a 6db antenna 15
meters up in a tree. The whole hotspot is built into an inverted
plastic bucket. The pringle's can antennas are very directional and
great for point to point work like you're doing.....and can be built and
rebuilt for nothing.

 

[Larry]

As I previously mentioned I do not have a signal strength meter and
used the standard Linux utility "iwconfig" to produce some sort of
data. It gave a reading of 6 for signal strength using the bare
adapter and as high as 23 with the wok I can only assume that whatever
the value of the increments that the ratio is accurate.

http://www.kismetwireless.net/
Kismet is the program for Linux

http://www.netstumbler.com/
Network STumbler for Windows is better and if you hook a GPS receiver to
the PC it will even log the position of every signal it finds that
couples directly to Google EArth! Way cool scanner for wifi at home or
riding around in a vehicle.





http://apradar.sourceforge.net/

http://sectools.org/

 

[Steve Lusardi]

Bruce,
I assume you know how to find the parabola's focal point. I won't bore you with a plan if you already know. Let me know if my
assumption is incorrect.
Steve

 

[Bruce]

http://www.kismetwireless.net/
Kismet is the program for Linux

Thanks for that. I had a couple of others but more is better.

http://www.netstumbler.com/
Network STumbler for Windows is better and if you hook a GPS receiver to
the PC it will even log the position of every signal it finds that
couples directly to Google EArth! Way cool scanner for wifi at home or
riding around in a vehicle.

Net Stumbles has a problem in that it only works with certain specific
Wireless chip sets. Unfortunately not the ones I have.

http://apradar.sourceforge.net/

http://sectools.org/

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

 

[Bruce]

Bruce,
I assume you know how to find the parabola's focal point. I won't bore you with a plan if you already know. Let me know if my
assumption is incorrect.
Steve

Yes, have the formula and know about the reflected sunlight method,
although that never seemed to work for me as when I put out a piece of
paper to measure the reflection it shaded the dish and the reflected
beam was too weak to see I'll have to get a special piece of
something transparent to use.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

 

[Bruce]

http://www.turnpoint.net/wireless/has.html

http://www.oreillynet.com/cs/weblog/view/wlg/448

http://binarywolf.com/249/pringles_cantenna.htm

http://www.netscum.com/~clapp/wireless.html

http://www.seattlewireless.net/PringlesCantenna

We get about 1.5 miles range from my 200mw hotspot with a 6db antenna 15
meters up in a tree. The whole hotspot is built into an inverted
plastic bucket. The pringle's can antennas are very directional and
great for point to point work like you're doing.....and can be built and
rebuilt for nothing.

I was going to built a tin can antenna but the devil is in the details
and so far I haven't been able to locate the tiny coax connectors that
connect to the wi-fi adapter and as I had read that at wi-fi
frequencies the loss in the usually available cable is nearly equal to
the gain of the antennas I have been a bit reluctant to try.

I am making a trip down to the "electronic district" tomorrow and,
after having written the above, will undoubtedly discover a source of
not only the connectors but also a coil of low loss cable that I can
get free

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

 

[Steve Lusardi]

Here's a tip. Construct a Tee piece say 2 inch across the top of the tee. Emanating at a 90 degree angle from the center of this 2
inch piece is a straight edge long enough to reach and pass the theoretical focal point....make an educated guess....Mark the
center of the parabolic dish with a magic marker. Use a tape measure or fasten a rod of any material perpendicular to the dish
center. Place the Tee piece anywhere on the surface of the dish and where the leg of the Tee crosses the center rod is the focal
point. Do this several times from different locations on the dish surface and average the crossing point on the perpendicular.
Simple.
Steve

 

[Bruce]

Here's a tip. Construct a Tee piece say 2 inch across the top of the tee. Emanating at a 90 degree angle from the center of this 2
inch piece is a straight edge long enough to reach and pass the theoretical focal point....make an educated guess....Mark the
center of the parabolic dish with a magic marker. Use a tape measure or fasten a rod of any material perpendicular to the dish
center. Place the Tee piece anywhere on the surface of the dish and where the leg of the Tee crosses the center rod is the focal
point. Do this several times from different locations on the dish surface and average the crossing point on the perpendicular.
Simple.
Steve

The point where a number of lines drawn at right angle to parabolic
dish intersect a line drawn at 90 degrees from the center of the dish.

I'm still going to get a sheet of Plexiglas, or something and try
focusing the dish, if for no other reason then to say that I did it



Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

 

[Bruce]

The shape of the antenna is not critical -- in practice a typical curved
bowl will work pretty much the same as a carefully constructed parabola.

Since I wrote the original I have done more research and it appears
that the current favorite is the offset feed dishes. One article has a
method of calculating the reflection angle and then cutting a string
for the far side of the dish and a second for the near side and mount
the feed at the point that the two strings meet.

Also I found several articles abut the construction of double quad
antennas and one of the articles showed the graphs of test with 12 db
gain.

I may change to the quad if I can get that much gain from a smaller
antenna as none of the tests I saw indicated that the dish produced
really astonishing gain.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

 

[You]

The shape of the antenna is not critical -- in practice a typical curved
bowl will work pretty much the same as a carefully constructed parabola.

It is a "Good Thing" you do NOT design Antenna Systems for a living,
because you would be out of business in a week. Don't give up your DAY
JOB.

 

[Larry]

Since I wrote the original I have done more research and it appears
that the current favorite is the offset feed dishes. One article has a
method of calculating the reflection angle and then cutting a string
for the far side of the dish and a second for the near side and mount
the feed at the point that the two strings meet.

Also I found several articles abut the construction of double quad
antennas and one of the articles showed the graphs of test with 12 db
gain.

I may change to the quad if I can get that much gain from a smaller
antenna as none of the tests I saw indicated that the dish produced
really astonishing gain.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

All of this discussion is MOST commendable, however it is also most
moot. All the gain in the world isn't going to overcome the natural
signal to noise ratio problem of inverse square law propagation from the
router's antenna against the intense solar and thermal noise of a sunny
day and a hot parking lot. The routers were specifically designed to
limit range to approximately 100 meters by reducing their power output
to a pittance, like your sellphone. Some routers only run 10-20mw into
horrible antennas made of a piece of pc board. The best ones only run
200mw tops into a 3db whip with space diversity receivers to hear your
20mw powerful beast coming back to them.

Highly directional antennas, just as with UHF analog TV and its
"ghosting" problem, do help reduce multipath propagation IF the antenna
is very tight patterned with very little back pattern, such as the
Pringle's Cantenna we've been building for years.

http://www.turnpoint.net/wireless/has.html

http://www.turnpoint.net/wireless/cantennahowto.html

These waveguide antennas have no rear radiation as the back of them is
solid metal. Antennas designed around HF, VHF even UHF are of little
use on microwaves, however cute. Waveguide antennas are used for radar
for a reason.

http://www.oreillynet.com/lpt/wlg/448

As you can see, their signal to noise ratio is quite impressive, much
more impressive than an open HF/VHF/UHF design.

"The test partner (AP side) signal results were virtually the same.
Interestingly, even at only 0.6 mile, we saw some thermal fade effect;
as the evening turned into night, we saw about 3db gain across the board
(it had been a particularly hot day: almost 100 degrees. I don't know
what the relative humidity was, but it felt fairly dry.)"

Our measurements between my hotspot 20 meters up an oak tree under an
inverted plastic bucket and the USAF enlisted barracks (I support the
troops) are very similar. Some days the combination of high humidity
and high temperature obscure my 200mw into a 6db co-linear quite badly
over the 1.2km path length to the roof of the 4 story barracks building
where the Pingle's Cantennas are mounted on various pipes to hide them
from paranoid schitzophrenic inspections.

Sky News in London gave the Pringle's Cantenna a boost, recently:

of course, blaming it for hacking, to infer it should be outlawed by the
UK nanny state.

http://www.youtube.com/results?search_query=Pringle's+Can+antenna&aq=f
There's lots of great videos from the "hackers". Oddly, most of them
look like anyone in your neighborhood, not some dangerous cyber
criminals.

I'm sure the news paranoids will win, at some point, and we'll all be
arrested by Homeland Security in the USA.

 

[Larry]

http://www.ab9il.net/wlan-projects/wifi1.html

We've tried his type of UHF antennas. The signal to noise ratio in
daylight is horrible from all the back pattern and many side lobes of these
designs for lower frequencies. A yagi isn't a good microwave antenna when
multipath reflections are eating up your data with odd pulsewidths and
pulses and the sun is boiling the molecules in the parking lot. You can
even see the S/N ratio drop by turning on a nearby incandescent light bulb!

Microwave antennas for both 2400 and 5200 Mhz (N band) are too easy to
build out of a Pringle's can or old juice can that can reduce background
radiation and thermal noise by a huge margin.

It's like looking at a distant object with your naked eye in bright
sunlight, squinting because of the glare (noise)......then, looking at the
same object through a paper towel cardboard tube that's been painted flat
black inside (pringle's cantenna). Without all the noise, the object is
much easier to look at. The same is true of these little round microwave
antennas, with or without the internal washer-made yagis to improve the
tuning and bandwidth.

 

[Bruce]

http://www.ab9il.net/wlan-projects/wifi1.html

Thanks for that URL, I hadn't seen it. The Linux hacks are
interesting.
Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

 

[Bruce]

All of this discussion is MOST commendable, however it is also most
moot. All the gain in the world isn't going to overcome the natural
signal to noise ratio problem of inverse square law propagation from the
router's antenna against the intense solar and thermal noise of a sunny
day and a hot parking lot. The routers were specifically designed to
limit range to approximately 100 meters by reducing their power output
to a pittance, like your sellphone. Some routers only run 10-20mw into
horrible antennas made of a piece of pc board. The best ones only run
200mw tops into a 3db whip with space diversity receivers to hear your
20mw powerful beast coming back to them.

Highly directional antennas, just as with UHF analog TV and its
"ghosting" problem, do help reduce multipath propagation IF the antenna
is very tight patterned with very little back pattern, such as the
Pringle's Cantenna we've been building for years.

http://www.turnpoint.net/wireless/has.html

http://www.turnpoint.net/wireless/cantennahowto.html

These waveguide antennas have no rear radiation as the back of them is
solid metal. Antennas designed around HF, VHF even UHF are of little
use on microwaves, however cute. Waveguide antennas are used for radar
for a reason.

http://www.oreillynet.com/lpt/wlg/448

As you can see, their signal to noise ratio is quite impressive, much
more impressive than an open HF/VHF/UHF design.

"The test partner (AP side) signal results were virtually the same.
Interestingly, even at only 0.6 mile, we saw some thermal fade effect;
as the evening turned into night, we saw about 3db gain across the board
(it had been a particularly hot day: almost 100 degrees. I don't know
what the relative humidity was, but it felt fairly dry.)"

Our measurements between my hotspot 20 meters up an oak tree under an
inverted plastic bucket and the USAF enlisted barracks (I support the
troops) are very similar. Some days the combination of high humidity
and high temperature obscure my 200mw into a 6db co-linear quite badly
over the 1.2km path length to the roof of the 4 story barracks building
where the Pingle's Cantennas are mounted on various pipes to hide them
from paranoid schitzophrenic inspections.

Sky News in London gave the Pringle's Cantenna a boost, recently:

of course, blaming it for hacking, to infer it should be outlawed by the
UK nanny state.

http://www.youtube.com/results?search_query=Pringle's+Can+antenna&aq=f
There's lots of great videos from the "hackers". Oddly, most of them
look like anyone in your neighborhood, not some dangerous cyber
criminals.

I'm sure the news paranoids will win, at some point, and we'll all be
arrested by Homeland Security in the USA.

Generally I agree with you (hard to argue with facts but the point
is, if with Antenna X, you have a very low signal strength and with
Antenna Y you have a much stronger signal then antenna Y will. in
nearly all cases, give better results.

All of the high gain wi-fi antennas, that I have looked at, mainly the
cans, quad, corner reflector, etc., which have high gain also have
good signal/noise ratios and are highly directive.

In addition, from the reading I have done, all of the high frequency
antennas are sensitive to the accuracy with which they are built -
tests I have seen on various cans showed a difference in gain that was
probably caused by fractions of a millimeter in inaccuracy.

Likely I could beg/buy/make a signal strength meter and SWR meter and
set up a proper antenna test range and spend days building a perfect,
antenna, but I'm not interested in that and all I want to do is log on
the Internet and read RBE.

The dish I built gave me a much better signal than the wifi adapter
alone however SHMBO is not happy with a wok hung on the wall - says it
does nothing for the decor and in Thailand a wok belongs in the
kitchen, so I am trying to build something that gives approximately
the same gain, or better, as the dish and is not so weird looking
hanging on the bed-sitter wall..

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)