Re: Homemade Antenna Choice, Jeff, et al, can you give me your best guess?
Re: Homemade Antenna Choice, Jeff, et al, can you give me your best guess?. Discuss Re: Homemade Antenna Choice, Jeff, et al, can you give me your best guess?, on Wireless Forums.
Re: Homemade Antenna Choice, Jeff, et al, can you give me your best guess?
On Tue, 1 Nov 2011 20:10:39 +0000 (UTC), Foxybaby
<Foxybaby@nospam.org> wrote:
>Jeff, can you please give me your best guess on which of
>these home-to-be-built antennas is likely to yield the
>highest gain using a linksys usb dongle -have two to choose
>from WSUB100 Range Plus or USB54GSC (which is better?).
I avoid using USB dongles unless they have an external antenna
connector. Neither of the two you've mentioned has an external
antenna connector. I have no idea which of the two is "better" since
I've never used either.
The problem with putting a reflector behind a USB dongles is that
you'll get different gains between xmit and receive. In receive, the
reflector picks up the aperature area of the dish and sends alost all
of it to the USB dongle. However, in transmit, the USB dongle sprays
RF in every direction, including directions where it misses the
reflector. This RF is lost, going to places unknown. I ran through
the calcs in a previous rant, but am too lazy to find it right now.
Bug me if you want numbers. As I vaguely recall, there was about a
10dB difference between xmit and receive. See dish illumination
issues under:
<http://www.w1ghz.org/antbook/contents.htm>
<http://www.w1ghz.org/antbook/chap6-0.pdf> (see spillover).
Methinks you'll be better off with a wireless client bridge, which
talks to the computer via ethernet, and usually has an external
antenna. The nice feature of this arragement is that it will work
with any OS that talks ethernet and that there are no flaky USB
drivers to deal with.
>Will
>be used under multiple OS's both windows 7, XP; Linux
I haven't checked, but I've had "issues" with USB dongles under Linux
in the past. Make sure it's well supported before buying.
>These
>radios are quite large like 3-4 inches in length, what is the
>location of the pickup point for signals under the case?
It's usually on the pointed end opposite the USB connector.
Something like this:
<http://802.11junk.com/jeffl/pics/wireless/DWL-122/index.html>
>If
>you don't have time, the most important questions are the
>antenna ones.
I'm always busy, never have time, and am lazy.
>Antenna 1(A1): kitchen collander with fine "screendoor" mesh
>(deeper curve than true parabola ), 27cm diameter 11 depth ;
>focal point at 4.14cm Dongle will be attached through fitted
>hole in center of the "dish" or possibly attached to wooden
>dowel also attached through hole in center of "dish" to allow
>for focal point adjustment.
I prefer my veggies raw instead of steamed.
<http://802.11junk.com/jeffl/antennas/Salad-Dish/index.html>
Like the above salad bowl, the colander is closer to a sphere than a
parabola. The result can be seen with the shiny bowl and a light as a
ring of light. No energy in the middle, along the center axis, then a
ring with all the power, After the ring, nothing. It's nowhere near a
point, so therefore, lousy gain.
>Antenna 2(A2): Umbrella size 86cm dia. ; 18.4 cm deep ;
>focal point 25 cm with aluminum foil glued to top of umbrella
>with some loss?? (how much? )from metal struts that support
>umbrella shape. Also some loss from metal center post of
>umbrella which extends just enough to hold wood or plastic
>dowel to hold the usb dongle. This is also not a true
>parabola but much shallower in curve than Antenna 1.
Much better. If you can get it close to a parabola, you'll have a
fine receive antenna, and a lousy transmit antenna due to reasons
previously mentioned. The struts will have little effect if they're
reasonably thin. If the wood is dry, there's little attenuation.
>Other factors to consider: wire mesh A1 vs mostly solid alum
>foil A2, shallowized parabola vs deepened parabola, metal
>pole in center of A1 vs no metal pole in A2
I don't understand the question.
>Also additional question is Mylar-the kind you see in metal
>baloons any better than heavy gauge alum foil for this, or
>does not matter?
RF travels on the surface of conductors. At 2.4GHz, the skin depth is
much smaller than the aluminized mylar plating. Making the aluminum
layer any thicker just adds weight and does nothing for gain. Try the
same plating thickness at lower RF frequencies and it won't work.
>I have not built either of these yet awaiting input from this
>group. Which one should I build and why?
What are you trying to accomplish? Why are you using a USB dongle?
Re: Homemade Antenna Choice, Jeff, et al, can you give me your bestguess?
The Alfa AWUS036H I suggested is Linux compatible. Kismet as well.
Granted $25 can't compete with $1, but the unit works well.
I really think you can't skimp on the usb dongle. I suppose you can save
some money rolling your own antenna if you have more time than money, or
you just want the experience.
This is probably the best page for biquad construction. Per Jeff's
suggestion, I used round loops rather than squares. The deal is you need
the proper circumference. The shape isn't as important, and it is easier
to get the circumference correct with a round loop. Marty does the
construction properly by using a coaxial feed. Jeff ran NEC2 on the
other scheme and it had a funny radiating pattern.
The reflector doesn't have to be copper, but soldering to anything else
is a lot of work. In fact, soldering to heavy copper clad isn't all that
easy unless you have a high wattage soldering iron or you have a small
propane torch. Building your own antenna is cheap IF you already own the
tools or have access to them. Otherwise you are buying hacksaws, copper
pipe, etc.
You can use the biquad to feed a dish for more gain. You can often get a
dish for free on Craigslist. The Dish or Direct TV dishes probably are
too small to be useful since the dish doesn't see the all the RF from
the biquad. You can get larger 24x36 elliptical dishes for free if you
stake out Craigslist.
A bit harder to find are the old MDS antennas that were sold for
"wireless cable". They use a parabolic reflector.
All that said, the Laird PA241-16 antenna I suggested is far less work,
and the difference between off the shelf and home built might be $10
when the dust settles.
Re: Homemade Antenna Choice, Jeff, et al, can you give me your best guess?
On Wed, 2 Nov 2011 04:05:47 +0000 (UTC), Foxybaby
<Foxybaby@nospam.org> wrote:
>I don't have a choice, money is tight and I got these two at
>an estate sale for $1 each.
Good price. Hopefully, they'll work.
>Did not know that. Read one source that said a deeper curve
>than parabola will attenuate some of the x-mit losses?
Yes, but within limits. Visualize your USB dongle at the focus of a
parabolic antenna. If the f/D (focal length divided by Diameter)
ratio is large, you have a shallow dish, with the USB dongle well
above the reflector surface. the result is that the dish only
collects a small part of the RF belched by the USB dongle. However,
if the f/D is small, you have a deep dish, where the dongle is located
deep into the dish. More of the RF it belches is collected by the
reflector. However, there's a limit. Let's pretend that the dongle
is in line with the edge of the dish. Half of the RF belched by the
dongle hits the dish, and the other half goes off in useless
directions. So, even with such a dish, you have a 3dB difference
between tx and rx. The steep sides of the deep dish also don't
contribute much to the gain of the antenna. So, the gain actually
drops as the f/D decreases. There's an optimum value of f/D. See the
graph at:
<http://www.antenna-theory.com/antennas/reflectors/dish3.php>
Since you're cost limited, I suggest you try one of these:
<http://www.freeantennas.com>
Cardboard, covered with aluminum foil, works well enough.
Also, note that it's fairly easy to build an antenna with gain up to
about 8-10dBi. Any more gain and the construction tolerances become
more than what you can do with cardboard, baleing wire, and duct tape.
>I mean the backing on the umbrella will be mostly continuous
>alum foil., whereas backing on the collander is mesh with
>holes. Also umbrella has metal pole in center that I will cut
>partially but there will still be a metal post at the center,
>so losses from that, probably minimal.
The holes in the colander are too small to have any effect. The
non-parabolic pattern will cause some gain loss. The marginal
parabolic shape of the umbrella, as aggrivated by the non-parabolic
shape of the foil between the umbrella ribs will cause some gain loss.
I'm not interested in modeling either design.
>I guess I don't have to worry about removing the thin nylon of
>the umbrella as the waves will go right through it and reflect
>on the foil on the other side, right?
I think the nylon is RF transparent. However, if it's been painted or
silk screened with something containing carbon or metallic powder,
you'll have a problem. Find a small piece and put it in the microwave
oven. If it gets hot, you loose. If it says cool, you win.
>Just trying to get any reasonable surfing connection to a
>hotspot.
Ummm... I'm not really interested in helping you do that, especially
since it seems you haven't obtained permission.
>BTW just started using
>Inssider, cuz heard Netstumber does not work under Win7.
Nestumbler is ancient and has not been updated for about 5 years.
Inssider is a good replacement. There are others. Bug me if you need
a list.
Re: Homemade Antenna Choice, Jeff, et al, can you give me your bestguess?
>> What are you trying to accomplish? Why are you using a USB
>> dongle?
I have opened a couple of dongles, cut the antenna foil and installed an
N connector. You need to plan mechanical support for the N connector,
but they both worked better than anything I had. Now I have an Alfa
AWUS036H and it works better than the inexpensive dongles I modified.
At one time I connected a modified dongle directly to the MFJ Yagi
and ran a USB cord into my boat. That worked well for a couple of years.
Mikek
Re: Homemade Antenna Choice, Jeff, et al, can you give me your best guess?
miso wrote:
> The AWUS036H is magic.
No it's not :)
The Realtek 8187L chipset that it uses is what's magic.
Any other cheap USB dongle with the same chipset and a removable antenna will perform just as well.
For "G" applications this chipset is hard to beat. The drivers work with the latest Linux flavours a lot better than they used to. Will now hold fulls peed.
Re: Homemade Antenna Choice, Jeff, et al, can you give me your bestguess?
On 11/2/2011 4:07 PM, Foxybaby wrote:
> Jeff Liebermann<jeffl@cruzio.com> wrote in
> news:d9j1b79dsea0qtrf7ed2s5pdhtrov5b7lt@4ax.com:
>
>> On Wed, 2 Nov 2011 04:05:47 +0000 (UTC), Foxybaby
>> <Foxybaby@nospam.org> wrote:
>>
>>> I don't have a choice, money is tight and I got these two
>>> at an estate sale for $1 each.
>>
>> Good price. Hopefully, they'll work.
>
> They do, but you're right, not strong enough, maybe I have to
> buy another Alfa.
>
>
> <snip>
>
>>
>> Since you're cost limited, I suggest you try one of these:
>> <http://www.freeantennas.com>
>> Cardboard, covered with aluminum foil, works well enough.
>
> Yeah looked at all the homemade sites. That's how I got the
> umbrella idea.
>
> <snip>
>
>>> I guess I don't have to worry about removing the thin nylon
>>> of the umbrella as the waves will go right through it and
>>> reflect on the foil on the other side, right?
>>
>> I think the nylon is RF transparent. However, if it's been
>> painted or silk screened with something containing carbon or
>> metallic powder, you'll have a problem. Find a small piece
>> and put it in the microwave oven. If it gets hot, you
>> loose. If it says cool, you win.
>
> Yeah thanks, I will test it in microwave.
>
>>
>>> Just trying to get any reasonable surfing connection to a
>>> hotspot.
>>
>> Ummm... I'm not really interested in helping you do that,
>> especially since it seems you haven't obtained permission.
>
> How am I going to ask if I cannot determine who owns it? It's
> reverses to a big Telecom. I don't have the equipment to
> follow the signal to their door. Besides their intention
> clearly is to leave it open. For all I know they are sniffing
> my data; even SSL is no longer safe.
>
>>
>>> BTW just started using
>>> Inssider, cuz heard Netstumber does not work under Win7.
>>
>> Nestumbler is ancient and has not been updated for about 5
>> years. Inssider is a good replacement. There are others.
>> Bug me if you need a list.
>
> Insidder works on 7 but the graph output is very hard to read
> from just a few feet away. With NS you got a solid graph that
> you could adjust your antenna from across the room. I tried NS
> on 7, it installed and opened ok but cannot see anything, even
> when set to xp compatible.
>
If you want to go for cheap, I'd build the biquad then just solder wires
to your $1 wifi dongle. You will have to inspect the PCB and cut out the
internal antenna. If you have the FCC number, it is possible to find a
photograph of the inside of the dongle.
You do realize that Netstumbler can be detected. It is not a passive
sniffer.
I haven't run NS in years, but I don't think it finds stealth WAPs. Thus
you can have interference without knowing it. There are Cygwin
implementations of kismet, though I never tried them myself. I'd sooner
try to set up a thumb drive linux.
Re: Homemade Antenna Choice, Jeff, et al, can you give me your best guess?
Foxybaby <Foxybaby@nospam.org> wrote:
> Thanks much for your reply.
> I don't have a choice, money is tight and I got these two at an estate
> sale for $1 each.
It's easy enough to stick the USB dongle into the side of a coffee can.
I theorized that two of the 2lb cans, soldered to make a longer can
would be the good solution, but the "customer" said the single coffee can
was better, because it didn't have such a narrow beam. He was just setting
them on the back of a couch in the window, using pillows to clamp it into
the right orientation to reach a router about a block away.
It needs to make a tight fit between the USB shield and the metal can.
later, I soldered a 10-24 nut to the can so I could mount it on a camera tripod,
but my friend got cable in the meantime, so that ended that quest.
--
Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5
> Foxybaby <Foxybaby@nospam.org> wrote:
> > Thanks much for your reply.
> > I don't have a choice, money is tight and I got these two at an estate
> > sale for $1 each.
>
> It's easy enough to stick the USB dongle into the side of a coffee can.
> I theorized that two of the 2lb cans, soldered to make a longer can
> would be the good solution, but the "customer" said the single coffee can
> was better, because it didn't have such a narrow beam. He was just setting
> them on the back of a couch in the window, using pillows to clamp it into
> the right orientation to reach a router about a block away.
>
> Other ideas:
> http://www.usbwifi.orcon.net.nz/
>
> My coffeecantenna:
> http://www.rahul.net/dold/clarence/u...42-800x600.jpg
> I used the calculator at
> http://www.turnpoint.net/wireless/cantennahowto.html
> to decide where to stick the USB dongle through the side.
>
> It needs to make a tight fit between the USB shield and the metal can.
> later, I soldered a 10-24 nut to the can so I could mount it on a camera tripod,
> but my friend got cable in the meantime, so that ended that quest.
So does it work very well with a dongle ?
Trying to use a plain USB dongle with a reflector has been less than satisfactory from my experience. The radiation pattern is very irregular. Just turning a dongle around in a reflector dish sees the gain go up and down.
I've got a spare Belkin adapter in a drawer and might give it a try.
Might get a better result by using a dongle with a dipole antenna and just drill a hole into side of can, insert dipole and strap dongle to exterior of can with a rubber band. Will give that a go.
Re: Homemade Antenna Choice, Jeff, et al, can you give me your best guess?
Dr Who <dead_letter_office@hotmail.com> wrote:
> So does it work very well with a dongle ?
I suppose that depends on your definition.
The two 2 lb cans gave better signal improvement, but the single 3 lb can
was more usable in the desired application.
> Trying to use a plain USB dongle with a reflector has been less than
> satisfactory from my experience. The radiation pattern is very irregular.
> Just turning a dongle around in a reflector dish sees the gain go up and
> down.
I think, when I was doing careful testing with Netstumbler, that I did see
a difference between front facing and rear facing in the can, but I forget.
I didn't try side facing.
I also tried a few woks and pie plates with various spacing of the dongle
from the reflector surface. I did some toying around with a used DirecTV
dish, but that was too much effort compared to the success of the coffee
can.
--
Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5
Re: Homemade Antenna Choice, Jeff, et al, can you give me your best guess? 
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