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usb adapter cantenna

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Anonymous
September 22, 2005 2:53:42 AM

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I would like to build a cantenna that uses a usb adapter as the active
element so that I can avoid the problem of losses in a long run of
coax cable and just use cat5 instead. But I haven't been able to find
much info on best dimensions and usb adapter placement within the can.
What is the best diameter can and how long should it be? Should the
usb adapter poke through the back of the can in the middle or into the
side of the can like in a regular cantenna? If through the side, how
far from the back of the can?

I plan to use an inexpensive Zonet ZEW2501 usb adapter.

Has anyone built something similar and how did it perform?

Thanks for any help.

More about : usb adapter cantenna

Anonymous
September 22, 2005 4:36:26 AM

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Thank you both for the info and links. What I have in mind is the same
as Clarence Dold's coffee can. I want to use a USB dongle. But he
doesn't give any dimensions or formulas for determining them on his
page. I suppose I could just experiment some but I'd prefer to have a
calculated starting point. What kind of antennas do the dongles use?
Are there different types? Is there a way to solder a pigtail onto a
dongle?
Anonymous
September 22, 2005 4:41:21 AM

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Well, just reread your reply and I see that you are in fact Clarence
Dold and that you used the formulas in another link you gave to decide
where to poke the hole.

Thanks !!! :) 
Related resources
Anonymous
September 22, 2005 7:40:13 AM

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bjs555 <aaa@bbb.com> wrote:
> I would like to build a cantenna that uses a usb adapter as the active
> element so that I can avoid the problem of losses in a long run of
> coax cable and just use cat5 instead. But I haven't been able to find

Are you talking about a game adapter at the end of cat 5, or a USB dongle
at the end of USB cable? cat 5 can go a lot farther. The USB should go 5
meters without an active repeater.

A friend was using a 6" diameter coffee can, which I found to have lower
gain than the 4" diameter two coffee can setup, but the larger can was
easier to point at an access point about two blocks away.

Bob Alston's coffee can
http://members.cox.net/tulsaalstons/Computer.htm
Clarence Dold's coffee can
http://www.rahul.net/dold/clarence/usb-can/im000742-800...
I used the turnpoint calculator to decide where to poke the hole.
http://www.turnpoint.net/wireless/cantennahowto.html

There are also many haphazard designs on the New Zealand page, using USB
dongles. http://www.usbwifi.orcon.net.nz/

Using a "standard" USB adapter, instead of the dongles, is on David
Taylor's site. http://www.nodomainname.co.uk/cantenna3/cantenna3.htm

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
Anonymous
September 22, 2005 7:44:18 AM

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On Wed, 21 Sep 2005 22:53:42 -0400, bjs555 <aaa@bbb.com> wrote:

>I would like to build a cantenna that uses a usb adapter as the active
>element so that I can avoid the problem of losses in a long run of
>coax cable and just use cat5 instead. But I haven't been able to find
>much info on best dimensions and usb adapter placement within the can.
>What is the best diameter can and how long should it be? Should the
>usb adapter poke through the back of the can in the middle or into the
>side of the can like in a regular cantenna? If through the side, how
>far from the back of the can?
>
>I plan to use an inexpensive Zonet ZEW2501 usb adapter.
>
>Has anyone built something similar and how did it perform?
>
>Thanks for any help.

A simple USB directional unit I made on the below page.

http://www.geocities.com/zoomkat/antenna.htm
Anonymous
September 22, 2005 9:09:09 AM

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bjs555 <aaa@bbb.com> wrote:
> Thank you both for the info and links. What I have in mind is the same
> as Clarence Dold's coffee can. I want to use a USB dongle. But he
> doesn't give any dimensions or formulas for determining them on his

The only calculation I used was the turnpoint page that I referenced.
http://www.turnpoint.net/wireless/cantennahowto.html

My coffee cans are 4" inside diameter. Plug that in to the turnpoint
calculator, and it will tell you that a wire radiator should be 1.7 inches
from the closed end of the can (measure inside). I made the assumption
that a USB dongle antenna should be at that same point.

The other dimension of interest is the length of the antenna element inside
the can. If I were putting the USB dongle in front of a simple reflector,
I would want it 31mm from the reflector. This suggests that the antenna
element of the dongle should be 31mm away from the wall of the can. The
antenna is at the tip of the dongle. Simply inserting the dongle inside
the can is conveniently near that dimension.

Here are some of the cans that I tried. I liked two 12 oz. Yuban cans the
best, but my friend likes the 3lb Yuban can, because it's easier to point.
According to the calculator, the 3lb can would be more efficient at
frequencies below the 2400 MHz of WiFi, but it works well for him.
The 12oz is even too large, but I couldn't get my hand inside a smaller can
to put the dongle in place. If this were a permanent setup, maybe you
could make it fit into a smaller can, but I was only playing, and I carry
the dongle with me, and don't normally use the can.

Can Diameter Length Wavlng 1/4wv TE11 TM01
3lb Yuban 6 7.5 5.50 1.38 1152 1505
Atkin's Bake 4 7 6.80 1.70 1729 2258
Hunt's Pasta 3.3125 5.5 9.40 2.35 2088 2727
Country Time 5 9 5.88 1.47 1383 1807
Nalley BigChunk 3.87 6 7.12 1.78 1787 2334
15oz coffee 4 5.5 6.80 1.70 1729 2258
Stagg Chili 3.3 4.2 9.50 2.38 2096 2737
12oz Yuban 3.875 5.3875 7.11 1.78 1785 2331

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
Anonymous
September 22, 2005 9:18:02 AM

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bjs555 <aaa@bbb.com> wrote:
> What kind of antennas do the dongles use? Is there a way to solder a
> pigtail onto a dongle?

Previously:
Jeff Liebermann <j...@comix.santa-cruz.ca.us> wrote:

http://members.cruzio.com/~jeffl/pics/wireless/DWL-122/
I removed the PIFA antenna, attached an SMA connector, and made some
bench tests for sensitivity, power out, and such.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
September 22, 2005 1:01:17 PM

Archived from groups: (More info?)

This looks like a possibility. But I'd rather leave the dongle intact
like you did.

His site has a great name ... Learn by Destroying ... I do, but too
often by accident ... haha. If I keep the site name in mind, I know
I'll feel better next time it happens.

Thanks.

On Thu, 22 Sep 2005 05:18:02 +0000 (UTC),
dold@XReXXusbXa.usenet.us.com wrote:

>bjs555 <aaa@bbb.com> wrote:
>> What kind of antennas do the dongles use? Is there a way to solder a
>> pigtail onto a dongle?
>
>Previously:
>Jeff Liebermann <j...@comix.santa-cruz.ca.us> wrote:
>
> http://members.cruzio.com/~jeffl/pics/wireless/DWL-122/
> I removed the PIFA antenna, attached an SMA connector, and made some
> bench tests for sensitivity, power out, and such.
Anonymous
September 22, 2005 3:10:03 PM

Archived from groups: (More info?)

On Thu, 22 Sep 2005 09:01:17 -0400, * <aaa@bbb.com> wrote:

>This looks like a possibility. But I'd rather leave the dongle intact
>like you did.

Unsolder 3 solder connections and an SMA connector. You can solder
the antenna back if you don't like it. No big deal. Unfortunately,
it's on a neighbors roof and I can't find the photos I took. Maybe
I'll do another.

>His site has a great name ... Learn by Destroying ... I do, but too
>often by accident ... haha. If I keep the site name in mind, I know
>I'll feel better next time it happens.

That reminds me.... If you don't know how to solder, find someone that
will do it for you. It's way too easy to destroy these small devices.

I think I've found a problem with this article on biquad antennas.
| http://homepages.ihug.co.nz/~redwood4/
The general construction is great but there's a problem with the way
the biquad wire ground connections were soldered to the outer copper
sleeve. The way a biquad works is that it's two full wave loops in
parallel. The only dimension that's really critical is the length of
the loops. They can be any shape including a circle, but the total
length is what determines resonance. In the photos, he soldered the
ground wires to the sleeve leaving about a 2mm length of tubing
between the ground points. Aesthetically, that looks very nice, but
the extra 2mm of loop length will cause a slight tendency to detune
the antenna lower in frequency. I'm not sure exactly how critical
this is. I'll play with an NEC2 model first to see what happens. My
guess(tm) is that the loop has to be shortened about 1-2mm to
compensate or the ground ends need to be soldered together.

I also take offense to the use of oversize coax and the large amount
of exposed center conductor at both ends of the oversized coax.
Losses at 2.4GHz hare high, but insignificant for short pieces of
coax. I would have used semi-rigid coax. The transition between the
huge center coax support for the biquad and my suggested semi-rigid
coax will be a big problem. There's no way to keep the center
conductor short. Therefore, methinks it would have been best to use a
single piece of .141 semi-rigid for *BOTH* the center support and the
pigtail. The .141 coax is stiff enough if the copper wire used in the
two loops is reduced in diameter. This will slightly affect the
bandwidth of the antenna, but not catastrophically.

In other words, change everything (one of my bad habits).

Otherwise, it's a very nice construction job and article on building a
biquad. However, I would like to have seem some test results and
comparisons with known antennas.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Anonymous
September 22, 2005 7:43:24 PM

Archived from groups: (More info?)

Jeff,

Thanks for the excellent information. I'm a circuit slob going back a
number of years but this RF stuff is like magic to a low speed guy.
Speaking of soldering, I used to be able to solder anything to
anything but somehow my fingers got thicker as I matured and surface
mount componets now strike fear in my heart :) 

I haven't gone very far into this project yet but my dongles (Zonet
ZEW2501) arrived today and I ran a few quick and dirty table top tests
using Netstumbler. I made a crude corner reflector by doubling up and
folding in half a piece of aluminum foil and could see improvements of
about 5 dB by placing it near the dongle and varying the position. A
Trendnet TEW226PC pcmcia card that I already had seems to work
slightly better but I can't put it on the end of a cable like I can
the usb dongle.

This is fun. Maxwell is probably smiling.

Bruce


On Thu, 22 Sep 2005 11:10:03 -0700, Jeff Liebermann
<jeffl@comix.santa-cruz.ca.us> wrote:

>On Thu, 22 Sep 2005 09:01:17 -0400, * <aaa@bbb.com> wrote:
>
>>This looks like a possibility. But I'd rather leave the dongle intact
>>like you did.
>
>Unsolder 3 solder connections and an SMA connector. You can solder
>the antenna back if you don't like it. No big deal. Unfortunately,
>it's on a neighbors roof and I can't find the photos I took. Maybe
>I'll do another.
>
>>His site has a great name ... Learn by Destroying ... I do, but too
>>often by accident ... haha. If I keep the site name in mind, I know
>>I'll feel better next time it happens.
>
>That reminds me.... If you don't know how to solder, find someone that
>will do it for you. It's way too easy to destroy these small devices.
>
>I think I've found a problem with this article on biquad antennas.
>| http://homepages.ihug.co.nz/~redwood4/
>The general construction is great but there's a problem with the way
>the biquad wire ground connections were soldered to the outer copper
>sleeve. The way a biquad works is that it's two full wave loops in
>parallel. The only dimension that's really critical is the length of
>the loops. They can be any shape including a circle, but the total
>length is what determines resonance. In the photos, he soldered the
>ground wires to the sleeve leaving about a 2mm length of tubing
>between the ground points. Aesthetically, that looks very nice, but
>the extra 2mm of loop length will cause a slight tendency to detune
>the antenna lower in frequency. I'm not sure exactly how critical
>this is. I'll play with an NEC2 model first to see what happens. My
>guess(tm) is that the loop has to be shortened about 1-2mm to
>compensate or the ground ends need to be soldered together.
>
>I also take offense to the use of oversize coax and the large amount
>of exposed center conductor at both ends of the oversized coax.
>Losses at 2.4GHz hare high, but insignificant for short pieces of
>coax. I would have used semi-rigid coax. The transition between the
>huge center coax support for the biquad and my suggested semi-rigid
>coax will be a big problem. There's no way to keep the center
>conductor short. Therefore, methinks it would have been best to use a
>single piece of .141 semi-rigid for *BOTH* the center support and the
>pigtail. The .141 coax is stiff enough if the copper wire used in the
>two loops is reduced in diameter. This will slightly affect the
>bandwidth of the antenna, but not catastrophically.
>
>In other words, change everything (one of my bad habits).
>
>Otherwise, it's a very nice construction job and article on building a
>biquad. However, I would like to have seem some test results and
>comparisons with known antennas.
Anonymous
September 22, 2005 7:43:25 PM

Archived from groups: (More info?)

On Thu, 22 Sep 2005 15:43:24 -0400, bjs555 <aaa@bbb.com> wrote:

>Thanks for the excellent information.

Not so fast. I'm having 2nd thoughts about my guesswork on how to
solder the biquad elements. I gotta do an NEC2 model before I can be
sure. I might actually be wrong. (What a horrible thought).

>I'm a circuit slob going back a
>number of years but this RF stuff is like magic to a low speed guy.

Yep. It's magic. That's the excuse I use to justify my exhorbitant
consulting fees. If it were easy or obvious, I couldn't be able to
charge as much.

>Speaking of soldering, I used to be able to solder anything to
>anything but somehow my fingers got thicker as I matured and surface
>mount componets now strike fear in my heart :) 

It's exposure to too much RF. When I got started in radio, I had a
full head of hair, steady hand, positive attitude, and full bank
account. After about 40 years of RF exposure, my hair is falling out,
my hand is shaking, my attitude is totally cynical, and my bank
account is depleted. Obviously, this could only be caused by RF
exposure. Who do I sue?

>I haven't gone very far into this project yet but my dongles (Zonet
>ZEW2501) arrived today and I ran a few quick and dirty table top tests
>using Netstumbler.

Good start. See what it does before you destroy it. Take some
pictures and post them somewhere. I'll suggest where to hack and cut.

>I made a crude corner reflector by doubling up and
>folding in half a piece of aluminum foil and could see improvements of
>about 5 dB by placing it near the dongle and varying the position.

5dB gain is not bad depending upon size.

>A
>Trendnet TEW226PC pcmcia card that I already had seems to work
>slightly better but I can't put it on the end of a cable like I can
>the usb dongle.

I was in a local coffee shop about a month ago and saw someone with a
ribbon cable extension from their PCMCIA card slot to the wireless
card hanging on the back of the laptop. Whatever works, I guess.

>This is fun. Maxwell is probably smiling.

Maxwell Smart (Agent 86) Don Adams is still very much alive and
possibly amused. The wireless shoe phone is sure to be released
shortly. We already have the "Cone of Silence".
http://en.wikipedia.org/wiki/Don_Adams
http://en.wikipedia.org/wiki/Get_Smart

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Anonymous
September 23, 2005 12:54:20 AM

Archived from groups: (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
> I think I've found a problem with this article on biquad antennas.
> | http://homepages.ihug.co.nz/~redwood4/
....
> In the photos, he soldered the ground wires to the sleeve leaving about a
> 2mm length of tubing between the ground points. Aesthetically, that
> looks very nice, but the extra 2mm of loop length will cause a slight
> tendency to detune the antenna lower in frequency.

I thought about that bit. I'm not sure that the redwood image isn't stolen
directly from Marty. The picture shows the biquad with 30.5 mm sides, and
a gap in the center, but the text on this page, Marty's and Trevor's
indicates that the legs are equal length.

Trevor isn't clear on this point. He speaks of a 244mm piece of wire, but
leaves a 1.5mm gap at the end. His shows the two legs right together at
the copper tube. Marty and redwood show it spread a bit, as if it would go
directly to the center pin if it continued.

You're suggesting that the ends soldered to the tube need to be just a
little shorter, so that the distance from corner past the tube where the
leg is connected into the (not connected) center conductor is 30.5cm?

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
September 23, 2005 3:13:40 AM

Archived from groups: (More info?)

Not a Cantenna but very easy to make with good gain.

http://homepages.ihug.co.nz/~redwood4

Peter

"bjs555" <aaa@bbb.com> wrote in message
news:kbd4j1lpkbqejd6j20huqn44vk9hqogdh3@4ax.com...
> Well, just reread your reply and I see that you are in fact Clarence
> Dold and that you used the formulas in another link you gave to decide
> where to poke the hole.
>
> Thanks !!! :) 
September 23, 2005 3:13:41 AM

Archived from groups: (More info?)

Well done! It's encouraging to read that you got a connection a mile
away with it!

One thing that bothers me about soldering a pigtail onto a circuit
board is that it may cause an impedance mismatch. What kind of circuit
is typically used to drive an antenna? A power transistor with low
output impedance? Some pictures I've seen show a dongle with an
antenna made of pc board traces. Where would I cut into the traces to
add a pigtail?

Thank you.

On Thu, 22 Sep 2005 23:13:40 +1000, "Pierre" <rainsford@ihug.com.au>
wrote:

>Not a Cantenna but very easy to make with good gain.
>
>http://homepages.ihug.co.nz/~redwood4
>
>Peter
>
>"bjs555" <aaa@bbb.com> wrote in message
>news:kbd4j1lpkbqejd6j20huqn44vk9hqogdh3@4ax.com...
>> Well, just reread your reply and I see that you are in fact Clarence
>> Dold and that you used the formulas in another link you gave to decide
>> where to poke the hole.
>>
>> Thanks !!! :) 
>
Anonymous
September 23, 2005 3:13:41 AM

Archived from groups: (More info?)

Pierre <rainsford@ihug.com.au> wrote:
> Not a Cantenna but very easy to make with good gain.

> http://homepages.ihug.co.nz/~redwood4

Nice photos. There is no author noted on the page, but since you're at the
same ISP: The TITLE of the page is "new document", when I save the bookmark.


--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
Anonymous
September 23, 2005 3:13:42 AM

Archived from groups: (More info?)

On Thu, 22 Sep 2005 09:13:21 -0400, * <aaa@bbb.com> wrote:

>Well done! It's encouraging to read that you got a connection a mile
>away with it!

You can go further but that would require more antenna gain.

>One thing that bothers me about soldering a pigtail onto a circuit
>board is that it may cause an impedance mismatch.

True. I would have used a smaller diameter semi-rigid coax cable for
the sole purpose of reducing the amount of exposed center conductor.
That appears as inductance and will create a substantial mismatch loss
if not properly compensated. If you look carefully at the
motherboards on the WRT54G series of router, you'll see a matching
section next to the TNC antenna connectors. That's specifically to
compensate for the exposed center conductor in the cheezy TNC
connectors or the coax cable to circuit board connection.
| http://www.linksysinfo.org/modules.php?name=Content&pa=...
Note the small parts on the leads going from the diversity switch IC
to the antenna connectors or coax. Those are the compensation
network.

>What kind of circuit
>is typically used to drive an antenna?

Actually the antennas are usually connected to PIN diode diversity
switch. That gets driven by a power amplifier IC. This is fairly
typical.
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3239/ln/

>A power transistor with low
>output impedance?

Nope. Usually an integrated power amplifier.

>Some pictures I've seen show a dongle with an
>antenna made of pc board traces.

That's the antenna.

>Where would I cut into the traces to
>add a pigtail?

I don't have a clue. Give me a model number and photo and I'll make a
guess.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Anonymous
September 23, 2005 3:24:39 PM

Archived from groups: (More info?)

I've been doing some more experimenting (nothing destroyed yet, but
soon no doubt).

I mentioned earlier that I got about 5 dB improvement with a quick and
dirty corner reflector. I rummaged around the kitchen and found a
spaghetti strainer that's roughly a parabola. It seemed to work about
as well as the corner reflector, but it was harder to hold in position
since I don't yet have an extension usb cable for my dongle. That
brings me to a whole set of questions about what is the best way to
have the antenna at some distance from the computer that's cabled to
the access point. But first a bit more about signal strength.
Unsurprisingly, I found that my signals lose a lot of strength going
through the brick walls of my apartment building. Maybe because they
hold water. I'd like to be able to use my notebook both inside and
outside my apartment. Is there a way to have both an inside and
outside antenna connected to the access point? Kind of like a
diversity antenna but with a separation of many feet rather than a few
inches. If I buy one of the access points with two antennas, can I
hook up an inside antenna to one connector and an outside antenna to
the other? Is there anything that can be done for a router with only
one antenna connector (parallel antennas - signals somehow isolated
and combined where needed - half-baked)? What is the best cable to
use? How far can I go? RF cable seems rather thick and difficult to
work with. Can I get away with thin cable?

Another thing I will try soon is poking a hole in a can of beans
(after dinner :)  and slipping it onto the external antenna of my
Netgear MR814 router. I figure I can just twist the can to get azimuth
control and tilt the whole router up and down to vary altitude. I
don't know how well the external antenna will feed into this crude
waveguide but it seems easy to try.

Here are some thoughts/questions about cabling to the access point and
wireless client:

I'd prefer not to use coax to the antennas since the coax is lossy and
hard to snake around. I bought the Zonex ZEW2501 dongles thinking that
I could put them in a can and use a long usb cable to put them
anywhere I wanted. But now I see that there's a limit of 5 meters to
usb cable length. Damn, I want to go about 10 meters. Etherenet cables
can run 100 meters so they would be fine. I could perhaps mount the
whole router inside a reflector and take care of one side of the link
that way. But what could I do about the dongles? I bought two Netgear
MR814 routers hoping I could use one as a client in place of the
dongle, but the routers don't seem to offer a client mode. Any way to
force it? Another (probably bad) idea is to use a junk computer
running Internet Connection Sharing. I haven't thought that through
completely but perhaps someone has done that or has better ideas.

Thanks.

Bruce Seiler
Anonymous
September 23, 2005 8:48:32 PM

Archived from groups: (More info?)

bjs555 <aaa@bbb.com> wrote:
> I mentioned earlier that I got about 5 dB improvement with a quick and
> dirty corner reflector. I rummaged around the kitchen and found a
> spaghetti strainer that's roughly a parabola. It seemed to work about
> as well as the corner reflector, but it was harder to hold in position

That sounds like some of the NZ work on the page
http://www.usbwifi.orcon.net.nz/

> outside my apartment. Is there a way to have both an inside and
> outside antenna connected to the access point?

My understanding is that this works, as long as the client can only see one
antenna at a time. Jeff Liebermann expands on this in a posting in this
group that you might find via a google search. My somewhat similar test is
that my connection would toggle back and forth between the good connection
and the poor connection when I had one stock antenna and one reflector.

> the other? Is there anything that can be done for a router with only
> one antenna connector (parallel antennas - signals somehow isolated

The pattern is pretty wide. My reflector works better to the sides than
the bare antenna did.

> Another thing I will try soon is poking a hole in a can of beans
> (after dinner :)  and slipping it onto the external antenna of my

That likely won't work. The radiator portion of the antenna would have to
be inside the can. Having it part in and part out would be unhelpful.

Better to build a reflector http://www.freeantennas.com EZ-12, printed on
photo paper for thick stock, with aluminum foil glued to the sail, provides
a substantial boost in signal.
http://www.rahul.net/dold/clarence/EZ12-windsurfer.jpg


> anywhere I wanted. But now I see that there's a limit of 5 meters to
> usb cable length. Damn, I want to go about 10 meters. Etherenet cables

5 meters of USB cable, but active repeaters can couple cables together. I
bought a five meter cable with an active repeater lump at one end that was
the same price as the 5 meter cable without the repeater.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
Anonymous
September 23, 2005 8:48:33 PM

Archived from groups: (More info?)

On Fri, 23 Sep 2005 16:48:32 +0000 (UTC),
dold@XReXXusbXa.usenet.us.com wrote:

>> Is there a way to have both an inside and outside antenna connected
>> to the access point?
>
>My understanding is that this works, as long as the client can only see one
>antenna at a time. Jeff Liebermann expands on this in a posting in this
>group that you might find via a google search. My somewhat similar test is
>that my connection would toggle back and forth between the good connection
>and the poor connection when I had one stock antenna and one reflector.

Interesting. I'll search for the posts. If I go with dual antennas, do
I need a splitter like this?:
http://www.hyperlinktech.com/web/signal_splitters.php
Maybe I'll have to get used to working with coax after all. How far
can it run before losses get unreasonable? Is 400 series cable the
right kind to use?


>> Another thing I will try soon is poking a hole in a can of beans
>> (after dinner :)  and slipping it onto the external antenna of my
>
>That likely won't work. The radiator portion of the antenna would have to
>be inside the can. Having it part in and part out would be unhelpful.

Afraid of that. Thanks for the tip. Saved me some time.


>Better to build a reflector http://www.freeantennas.com EZ-12, printed on
>photo paper for thick stock, with aluminum foil glued to the sail, provides
>a substantial boost in signal.
>http://www.rahul.net/dold/clarence/EZ12-windsurfer.jpg

Your Netgear router looks just like mine. I'll try the windsurfer. I
picked up two of the 802.11b Netgears for $15 each (after $20 rebate)
at tigerdirect.com. Couldn't resist the price.


>> anywhere I wanted. But now I see that there's a limit of 5 meters to
>> usb cable length. Damn, I want to go about 10 meters. Etherenet cables
>
>5 meters of USB cable, but active repeaters can couple cables together. I
>bought a five meter cable with an active repeater lump at one end that was
>the same price as the 5 meter cable without the repeater.

Yes, I found active usb cables for $20 each at:
http://www.pccables.com/cgi-bin/orders6.cgi?action=Show...


Bruce
Anonymous
September 23, 2005 9:43:41 PM

Archived from groups: (More info?)

bjs555 <aaa@bbb.com> wrote:
> Interesting. I'll search for the posts. If I go with dual antennas, do
> I need a splitter like this?:

I was only referring to a dual-antenna WAP, like my SMC7004WFW. I don't
know about splitting a single antenna.

> Your Netgear router looks just like mine. I'll try the windsurfer. I
> picked up two of the 802.11b Netgears for $15 each (after $20 rebate)
> at tigerdirect.com. Couldn't resist the price.

Netgear WGB511 802.11g Wireless Networking Kit
WGR614v4 Router and WG511 CardBus card that I have.
<http://www.amazon.com/exec/obidos/tg/detail/-/B000117DG...;
The price fluctuates a lot. There aren't any rebates today. I think I was
around $30 for the pair. I'm a rebate junkie.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
September 24, 2005 2:33:21 AM

Archived from groups: (More info?)

As the builder of the redwood variant, perhaps I should comment.

Length was originally a bit longer and I had made a few of differing
lengths, mounted them and did some rather crude but bottom line effective
tests using a simple field strength meter (diode type!). It was the length
shown which is the same as the martybugs variety that gave the best result.
Admittedly we tend to use the lower channels, 1,6 rather than the higher end
at 11 at our locations.

The coax, point is made....Cheap and available. In New Zealand, one does not
have quite the abilities to get small lengths of more suitable coax. It was
a bit of a gamble but the best we could readily find locally.

Like Jeff, I have been involved with RF as an amateur and professionally off
and on for over 45 years so am very aware of all the optimum theory and
parts but when you are working to a very limited budget in a place well
removed from mainstream and without your usual facilities (I base in
Melbourne, Australia), you tend to work by the seat of your pants. The real
trick is that it is reasonably reproducible to a point that works. The
biquad is comparatively wideband, more so than a stub in a can! so has a bit
more tolerance anyway.

I leave it open for the average person to produce something so simply
effective using only handyman tools and easily obtained items. Hopefully
some will take the idea and experiment further and produce something even
better, such is most of the experimental nature of handling RF and antennas
et al.

One for you, Jeff, it certainly beats tuning a 10Ghz etched filter with
silver paint and a scalpel under a microscope while watching a spec ani.!
That was in the '80s and culminated in our setting the inaugural 10 Ghz VK
DX two way record! The eyesight was a lot better then too.

Peter

<dold@XReXXusbXa.usenet.us.com> wrote in message
news:D gv5ls$hhi$1@blue.rahul.net...
> Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
> > I think I've found a problem with this article on biquad antennas.
> > | http://homepages.ihug.co.nz/~redwood4/
> ...
> > In the photos, he soldered the ground wires to the sleeve leaving about
a
> > 2mm length of tubing between the ground points. Aesthetically, that
> > looks very nice, but the extra 2mm of loop length will cause a slight
> > tendency to detune the antenna lower in frequency.
>
> I thought about that bit. I'm not sure that the redwood image isn't
stolen
> directly from Marty. The picture shows the biquad with 30.5 mm sides, and
> a gap in the center, but the text on this page, Marty's and Trevor's
> indicates that the legs are equal length.
>
> Trevor isn't clear on this point. He speaks of a 244mm piece of wire, but
> leaves a 1.5mm gap at the end. His shows the two legs right together at
> the copper tube. Marty and redwood show it spread a bit, as if it would
go
> directly to the center pin if it continued.
>
> You're suggesting that the ends soldered to the tube need to be just a
> little shorter, so that the distance from corner past the tube where the
> leg is connected into the (not connected) center conductor is 30.5cm?
>
> ---
> Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
>
Anonymous
September 24, 2005 9:09:17 AM

Archived from groups: (More info?)

A can with a USB adapter is on my list of "things to do."
I have had more experience with a 12 inch mixing bowl as on the New
Zealand site.
Works beyond amazingly well and very simple to use.
You sort of point the dish in a direction rather than aiming it.
The dimensions that seem to be optimal is a 12 inch bowl.
The dongle antenna is 7 inches from the base of the bowl.
I have tried various dongle brands.
Last week I tried g vs b.
Jeff Lieberman has explained that g receivers are newer electronics
with more sensitivity.
The Gigafast b is very good. However the link strength is too low for
Netstumbler use - link quality is very high at low signal strength. You
use the utility that comes with the adapter.
The Trendnet brand works well with Netstumbler.
Signal strenth measurement seems to be higher whereas Link quality is
not so off the scale.
Maybe Jeff can comment on this - is it just measurement diffirences on
the scale by the diffirent brands ?
Reception seemed better in some cases than the Gigafast but not in some
cases.
I tried a G Inexq - not really much diffirence but perhaps as Jeff
suggested in fringe reception ?
Most of these dongles seem to use a more oddball chipset - the Zydas
brand .
As a general note - it seems to be a rather good chipset and for
general use for beginners among the easiest to set up . Perhaps others
have comments good or bad as well.
I tried a D-Link dongle and was not impressed compared to the Zydas.
Has anyone tried a Linksys/ Network Everywhere USB adapter - has a more
standard Prism chipset ?
According to the New Zealand website 12 inches seems to be their
optimum.
Has anyone built one of the satellite dish ( Primestar) antennas with a
dongle adapter ?
Would a larger size help in reception.
What would be the focal length to use to build one.
hard to use on a car seat though.
Have fun.
All I can tell you that without the serving bowl reception is not much
in comparison.
dold@XReXXusbXa.usenet.us.com wrote:
> bjs555 <aaa@bbb.com> wrote:
> > Interesting. I'll search for the posts. If I go with dual antennas, do
> > I need a splitter like this?:
>
> I was only referring to a dual-antenna WAP, like my SMC7004WFW. I don't
> know about splitting a single antenna.
>
> > Your Netgear router looks just like mine. I'll try the windsurfer. I
> > picked up two of the 802.11b Netgears for $15 each (after $20 rebate)
> > at tigerdirect.com. Couldn't resist the price.
>
> Netgear WGB511 802.11g Wireless Networking Kit
> WGR614v4 Router and WG511 CardBus card that I have.
> <http://www.amazon.com/exec/obidos/tg/detail/-/B000117DG...;
> The price fluctuates a lot. There aren't any rebates today. I think I was
> around $30 for the pair. I'm a rebate junkie.
>
> --
> ---
> Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
Anonymous
September 24, 2005 12:51:33 PM

Archived from groups: (More info?)

On Fri, 23 Sep 2005 13:24:05 -0400, bjs555 <aaa@bbb.com> wrote:

>If I go with dual antennas, do
>I need a splitter like this?:
>http://www.hyperlinktech.com/web/signal_splitters.php

No. That antennas are turned on only one at a time. That means you
only get the gain of one antenna and cannot combine the signals to get
more gain. Just use one antenna port.

>Maybe I'll have to get used to working with coax after all. How far
>can it run before losses get unreasonable? Is 400 series cable the
>right kind to use?

LMR-400 coax is a good coax for long runs. 6.8dB/100ft loss at
2.4GHz. You will also lose about 0.5dB per connector pair so even a
zero length coax extension will have 1dB of loss. Add a pigtail and
you add 2 more connectors. How far you can go requires that I
calculate the fade margin. I've done this about 20 times. Use Google
Groups advanced search to look for "fade margin".

For a rule of thumb, 6dB loss will cut your range in half. 12dB will
cut it to 1/4th.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Anonymous
September 24, 2005 1:21:26 PM

Archived from groups: (More info?)

On Fri, 23 Sep 2005 22:33:21 +1000, "Pierre" <rainsford@ihug.com.au>
wrote:

>As the builder of the redwood variant, perhaps I should comment.

Oh-oh.

>Length was originally a bit longer and I had made a few of differing
>lengths, mounted them and did some rather crude but bottom line effective
>tests using a simple field strength meter (diode type!).

I could never get consistent results using a field strength meter
(diode hanging on my DVM with two resistors and a cap to filter the
rectified DC). I now have a very old but useful spectrum analyzer.
However, it only goes to 1.2GHz so I use an MMDS downconverter for a
test receiver. My signal source is a 2.4GHz WISP transmitter located
on a mountain top about 3 miles away. Line of sight and minimal local
reflections. Also saves on the cost of a signal source.

>It was the length
>shown which is the same as the martybugs variety that gave the best result.
>Admittedly we tend to use the lower channels, 1,6 rather than the higher end
>at 11 at our locations.

http://802.11junk.com/jeffl/pics/antennas/Biquad/index....

Note that the VSWR curve is quite flat over the entire band. That
allows considerable creativity and variation in construction. I'm
tempted to compromise this broad bandwidth by using a smaller diameter
wire. That will make it much easier to build.

The problem is that the above model is directly from the original
Trevor Marshall implementation without any of the fine details, such
as the coax cable feed diameter thrown into the puzzle. I'll try to
add these in the next few days and see what breaks. I really don't
know (yet) if it will have a significant effect. I'm also going to
change the quad antennas to a loop as putting corners on the antenna
is a waste of effort and actually quite difficult to do accurately.
The only critical dimension is the length of each loop, not the shape.
But first, I gotta learn how to use the 4NEC2 optimizer.

>The coax, point is made....Cheap and available. In New Zealand, one does not
>have quite the abilities to get small lengths of more suitable coax. It was
>a bit of a gamble but the best we could readily find locally.

Well, it's not so much the choice of coax that I'm complaining about.
It's the effects of the transitions. You could have used a smaller
diameter coax for the center feed if you had a better way to support
the biquad elements. Methinks I can do that by using smaller diameter
copper wire for the elements. A piece of RG-174 should work if
stiffened with some solder slopped on the outside braid. Make your
own semi-rigid coax. That should also solve the problem with the
rather sharp right angle turn required where it exits the reflector.
In addition, it will eliminate one coax diameter transition and
eliminate the long exposed center conductor where it hits the radio
circuit board.

>The real
>trick is that it is reasonably reproducible to a point that works. The
>biquad is comparatively wideband, more so than a stub in a can! so has a bit
>more tolerance anyway.

Yep. Compare the can and biquad VSWR plots at the band ends:
| http://802.11junk.com/jeffl/pics/antennas/coffee2400/sl...
| http://802.11junk.com/jeffl/pics/antennas/Biquad/slides...
I've only built two coffee can feeds. I wasn't thrilled. Biquad is
much better.

I won't say anything nice about my attempt at building a biquad inside
a 6" outdoor box:
| http://802.11junk.com/jeffl/pics/antennas/biquad2/index...
Major mistake was using nylon insulators. They're hygroscopic and
caused the antenna to screw up badly after about 3 days.

>I leave it open for the average person to produce something so simply
>effective using only handyman tools and easily obtained items. Hopefully
>some will take the idea and experiment further and produce something even
>better, such is most of the experimental nature of handling RF and antennas
>et al.

Yep. Learn by Destroying. One does not understand antennas until one
builds a few that don't work as expected.

Idea for you. Go to stationary store and find some foam board. It
comes in various thicknesses but most commonly about 1/4" thick. 1/2
wave aluminum foil reflector on one side of the board. Copper tape a
biquad or patch antenna on the other side. Maybe 4 folded dipoles
playing vertical collinear. Pile additional layers to get the correct
thickness. Shove coax through foam and make connection with glue or
aluminum duct tape.

>One for you, Jeff, it certainly beats tuning a 10Ghz etched filter with
>silver paint and a scalpel under a microscope while watching a spec ani.!
>That was in the '80s and culminated in our setting the inaugural 10 Ghz VK
>DX two way record! The eyesight was a lot better then too.

Congrats and nicely done. I've built filters out of copper pipe
fittings but never tried to do anything at 10GHz (other than use
converted commercial equipment). I did machine an interdigital filter
at X-band but I never could get it to work right.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Anonymous
September 24, 2005 4:37:28 PM

Archived from groups: (More info?)

On Sat, 24 Sep 2005 13:44:17 -0400, bjs555 <aaa@bbb.com> wrote:

>If I understand you correctly, that would mean
>that a dish type reflector is more effective on a receiver than a
>transmitter.

No. A properly designed dish and feed have the same gain in both xmit
and receive. In improperly designed system, with large amounts of
overspray from the feed, will cause the dish to less than the
theoretical maximum gain in transmit and about the same as the
theoretical gain in receive.

>Picturing the radio waves as rays of light, the rays
>would be nearly parallel at a receiver very far from a transmitter.
>Thus, nearly all the captured rays would go to the focus of the
>reflector. For a reflector a few inches from the transmitter, however,
>many rays would "spill out" and wouldn't contribute to the transmitted
>beam. So it seems to make more sense to put a reflector on a client
>antenna rather than an access point antenna. Is this verified by
>experiment? (I know, why don't I do it - not fully set up yet.)

This is rather muddled. A client radio, access point, repeater, and
just about any type of wireless device works best when the transmit
and receive gains are about the same. More specifically, they work
best in a symmetrical system, where the fade margin on both directions
is about the same. If you radically increase the gain in one
direction, you obtain no additional range because the signal in the
other direction hasn't improved at all. Whether you create such a
situation by adding a tx power amplifier or by throwing together a
poorly designed antenna system is not important.

>Another question:

Groan...

>I did some searching for IC RF amps starting from the page you gave in
>an earlier post. I found this Maxim data sheet:
>http://pdfserv.maxim-ic.com/en/ds/MAX2240.pdf
>which shows an application circuit at the top. In the circuit, the
>signal is shown ac coupled to the antenna through a 10 pF cap. Is that
>typical?

Chuckle. I just love the polarity marking in the 10pf capacitor,
especially since ceramic caps are not polarized.

The reactance of 10pf at 2.4Ghz is:
Xc = 1 / (2 * PI * freq * C)
Xc = 1 / (2 * 3.14 * 2.4*10^9 * 10*10^-12)
Xc = 6.6 ohms
Compared to the 50 ohm load, that will result in about a 10% loss or
about 1dB. Tolerable. Looks like the output matching network is
trying to compensate for some lead inductance in the flip chip. The
10pf is therefore probably part of this matching network, in which
case the loss is probably much less. I'm too lazy to model it to be
sure.

If you're thinking of making your own amplifier, there are better
chips that put out more power and in easier packages. Flip chips were
made for automatic vapor reflow soldering and are not really suitable
for do it thyself breadboards.

You might wanna dig through the collection of 802.11a/b/g app notes
at:
| http://www.maxim-ic.com/appnotes10.cfm/ac_pk/38#12
for anything interesting. Maxim also sells prototype boards with the
chip and all supporting circuitry ready to test and clone.

>Would I connect an external antenna at the RF out end of the
>cap?

Reading between the lines of your question, I detect that what you
really want to know is where to cut the trace on your USB adapter and
attach either a pigtail, connector, or antenna. Yes, it's on the
antenna side of the capacitor to avoid having DC appear on the
antenna. No, I don't have a clue where you should cut because I don't
have the board layout, photo, schematic, or the time.

>Do I cut any traces to an existing antenna?

See above.

>Are compensation
>circuits (not sure these apply to RF) sometimes used?

Always used in the better radios. It's almost impossible to build a
perfect 50 ohm match. The designers take their best shots and
compensate for any mismatches with a matching network.

>Also, at this page:
>http://www.nodomainname.co.uk/ma401/ma401.htm
>the author describes a way to add an external antenna to a particular
>wifi card by removing an inductor and adding 2 150 pF caps. Why is he
>doing that?

Probably because he had some 150pf caps handy or couldn't handle the
tiny 10pf or so capacitors. Self resonance is a big problem and needs
to be avoided. 150pf is way too big. He added them because Netgear
apparently has some DC on the ungrounded antenna elements and
diversity PIN diode switch. External antennas should be AC coupled to
prevent accidentally shorting parts of the radio to ground.

>You gave some pictures of a dongle that you modified for an external
>antenna. Where did you connect to the circuit?

I also mentioned that it's on a neighbors roof and I can't find the
photos. The PIFA antenna has 3 soldered connections. The middle
connection is the 50 ohm point and is where you connect the coax
center conductor. The nearest solder blob is ground. That's the
shield point. The other solder blob is just for mounting. I used a
PCB mount SMA connector and as much ground as I could solder.

>I'm thinking now that the best approach might be a something like
>this:
>http://www.nodomainname.co.uk/cantenna3/cantenna3.htm
>where a proper feed is made into the waveguide without using RF
>cables.

Note that the Compaq WL215 is an Orinoco Gold classic card with an
external coax connector. He could have done it without cramming the
whole mess into the tube. I personally don't find anything wonderful
about the arrangement.

>Sorry for asking so many questions but I find this topic so
>interesting. And thanks for the antenna theory references.

No problem.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Anonymous
September 24, 2005 9:56:42 PM

Archived from groups: (More info?)

> I'm thinking now that the best approach might be a something like
> this:
> http://www.nodomainname.co.uk/cantenna3/cantenna3.htm
> where a proper feed is made into the waveguide without using RF
> cables.

But there is an RF cable, it's from the Compaq WL110 card via a small
pigtail to an N type connector and then via a bit of RG195 coax which is
then stripped back to make the feed into the cardboard can.

I'm not sure I'd go so far as to call it a "proper" feed but a quick and
dirty bodge. Scraping the laquer off the foil liner and soldering to
self adhesive copper tape really is a bodge! :) 

David.
Anonymous
September 24, 2005 9:56:43 PM

Archived from groups: (More info?)

err ... minimimum amount of RF cable :) 

Good man - you show no fear of opening and improving these cards and
dongles. Thanks for the good pics and tips on your web pages.

Well, could the cable be eliminated completely if you soldered a wire
directly to the RF outpoint point on the circuit board and duct taped
the whole card to the outside of the cantenna with the wire poking
through? I wouldn't know what to do about the ground braid. Maybe I'm
all wet.

Bruce


On Sat, 24 Sep 2005 17:56:42 GMT, David Taylor <djtaylor@bigfoot.com>
wrote:

>> I'm thinking now that the best approach might be a something like
>> this:
>> http://www.nodomainname.co.uk/cantenna3/cantenna3.htm
>> where a proper feed is made into the waveguide without using RF
>> cables.
>
>But there is an RF cable, it's from the Compaq WL110 card via a small
>pigtail to an N type connector and then via a bit of RG195 coax which is
>then stripped back to make the feed into the cardboard can.
>
>I'm not sure I'd go so far as to call it a "proper" feed but a quick and
>dirty bodge. Scraping the laquer off the foil liner and soldering to
>self adhesive copper tape really is a bodge! :) 
>
>David.
Anonymous
September 24, 2005 10:27:14 PM

Archived from groups: (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
> Incidentally, the same problem with feed "overspray" or "spillover"
> happens with foil reflectors hung on vertical omnidirectional antennas
> as in www.FreeAntennas.com. However, the effect is much smaller than
> the 15dB loss in the pizza dish reflector because reflector captures
> most of the RF from the vertical and redirects it in a useful
> direction. For example, if the reflector covered a 120 degree azimuth
> wedge (looking down on the antenna), two thirds of the transmitted RF
> will go to places unknown, while one third will hit the reflector.
> That's about 5dB loss which isn't bad considering that even the best
> dish antennas and feeds have about a 3dB illumination loss.

I don't think your math is accurate. If you consider the 3dB beamwidth to
be 50 degrees, then the 50 degrees of "overspray" is headed in the right
direction. The EZ-12 looks like 120 degrees, so the effect should be 50 %
of the radiated power going in the right direction.

Comparing your NEC plot of a BiQuad to the NEC plot of the EZ-12 looks like
a minimal difference. The EZ-12 has a 3dB beamwidth of 50 degrees, your
biquad is 60. The charts are based differently, but it looks like you have
11.1 dB of gain, the Ez-12 11.41.

And the EZ-12 is, as the name implies, easy to build.


---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
Anonymous
September 24, 2005 10:27:15 PM

Archived from groups: (More info?)

On Sat, 24 Sep 2005 18:27:14 +0000 (UTC),
dold@XReXXusbXa.usenet.us.com wrote:

>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
>> Incidentally, the same problem with feed "overspray" or "spillover"
>> happens with foil reflectors hung on vertical omnidirectional antennas
>> as in www.FreeAntennas.com. However, the effect is much smaller than
>> the 15dB loss in the pizza dish reflector because reflector captures
>> most of the RF from the vertical and redirects it in a useful
>> direction. For example, if the reflector covered a 120 degree azimuth
>> wedge (looking down on the antenna), two thirds of the transmitted RF
>> will go to places unknown, while one third will hit the reflector.
>> That's about 5dB loss which isn't bad considering that even the best
>> dish antennas and feeds have about a 3dB illumination loss.

>I don't think your math is accurate.

That's been known to happen. That reminds me. My calculator
batteries need replacement. 3ea N batteries. Ouch.

>If you consider the 3dB beamwidth to
>be 50 degrees, then the 50 degrees of "overspray" is headed in the right
>direction. The EZ-12 looks like 120 degrees, so the effect should be 50 %
>of the radiated power going in the right direction.

Nope. We have a small apples and oranges problem. The USB feed for a
pizza dish is a 3 dimensional problem while the EZ-12 and such are
mostly 2 dimensional. The USB source is treated almost like an
isotropic point source (incandescent light bulb), while the omni
antenna driving the EZ-12 is mostly a linear source (fluorescent light
bulb). The illuminated areas are calculated somewhat differently.

For USB, you take the illuminated surface area of the dish, as viewed
from the USB dongle. The ratio of the illuminated area of the dish,
as a fraction of the spherical surface area of a sphere with the same
radius as the feed to dish radius, is the illumination loss (in dB).
That's because anything radiated by the USB dongle that does NOT hit
the dish, is treated as a loss.

For the EZ-12 type reflector, the problem is mostly 2 dimensional.
The illumination loss is simply the ratio of the wedge angle that hits
the reflector, as divided by a circle with a radius equal to the feed
to reflector distance. So, 120 degrees would be 1/3 of a circle or:
dB = 10 log (0.3333) = -4.77 dB.

Obviously both my models are crude assumptions. The USB dongle is not
really an isotropic radiator. The vertical dipole in the EZ-12 is not
a perfectly linear radiator. However, the approximations are good
enough for a first approximation and are certainly good enough for a
comparison.

>Comparing your NEC plot of a BiQuad to the NEC plot of the EZ-12 looks like
>a minimal difference. The EZ-12 has a 3dB beamwidth of 50 degrees, your
>biquad is 60.

I'll throw together a 3D plot and demonstrate the difference between a
biquad and a corner reflector. I'll also try to determine if the
EZ-12 gain calc uses the transmit performance or the receive. As I
mentioned, there is some loss in using a non-optimized feed for the
EZ-12 but it's not as huge as using a pizza dish with a USB dongle
feed.

>The charts are based differently, but it looks like you have
>11.1 dB of gain, the Ez-12 11.41.

I would call both of them 10dB based on all the various accuracies,
assumptions, and significant figures. Most of my tests in trying to
measure antenna gains and patterns have resulted in at *BEST* +/- 3dB
accuracy. Usually, somewhat worse.

>And the EZ-12 is, as the name implies, easy to build.

Granted.

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

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Anonymous
September 24, 2005 10:28:52 PM

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Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
> I have some not very nice comments to make about using a reflector
> with a USB dongle feed. The basic problem is that the original PIFA
> or circuit board antenna has roughly a hemispherical antenna pattern.
> That means that transmissions from the dongle will go in all
> directions and only some of which will hit the dish, reflect toward
> the receiver, and provide useful gain.

Does the wire in a biquad transmit all of it's power toward the copper
plate?

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
Anonymous
September 24, 2005 10:28:53 PM

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On Sat, 24 Sep 2005 18:28:52 +0000 (UTC),
dold@XReXXusbXa.usenet.us.com wrote:

>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
>> I have some not very nice comments to make about using a reflector
>> with a USB dongle feed. The basic problem is that the original PIFA
>> or circuit board antenna has roughly a hemispherical antenna pattern.
>> That means that transmissions from the dongle will go in all
>> directions and only some of which will hit the dish, reflect toward
>> the receiver, and provide useful gain.

>Does the wire in a biquad transmit all of it's power toward the copper
>plate?

No. It transmits equal "forward" power toward the target and
"incident power toward the reflector. The "incident" signal that hits
the reflector bounces off the reflector and back towards the target.
The position of the reflector is adjusted so that the "incident"
signal and the "forward" signal are in phase and combine to yield
additional gain.

One could build a biquad without a reflector, but the gain would be at
least 3dB less. There would also be no physical isolation between the
antenna and the RF circuitry, which can create all kinds of complex
interactions.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Anonymous
September 24, 2005 11:09:17 PM

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> Well, could the cable be eliminated completely if you soldered a wire
> directly to the RF outpoint point on the circuit board and duct taped
> the whole card to the outside of the cantenna with the wire poking
> through? I wouldn't know what to do about the ground braid. Maybe I'm

That's pretty much what the first one was:-

http://www.nodomainname.co.uk/cantenna/IMG_0384s.jpg

No need to even solder anything as it's just the Netgear MA101 with the
plastic shell removed.

David.
Anonymous
September 25, 2005 2:18:31 AM

Archived from groups: (More info?)

> external coax connector. He could have done it without cramming the
> whole mess into the tube. I personally don't find anything wonderful
> about the arrangement.

Nope nothing wonderful. The reason it was all in the tube was so that
there was only one cable, the USB one coming out. Plenty of space in
the rear of the pipe so loads of space for the radio. Easier to do that
than to find another box to piggy back on to and the point of using the
USB was to have as little RF loss in 15' of thin coax.

David.
Anonymous
September 25, 2005 2:51:47 AM

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Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
> dold@XReXXusbXa.usenet.us.com wrote:
>>If you consider the 3dB beamwidth to
>>be 50 degrees, then the 50 degrees of "overspray" is headed in the right
>>direction. The EZ-12 looks like 120 degrees, so the effect should be 50 %
>>of the radiated power going in the right direction.

> Nope. We have a small apples and oranges problem. The USB feed for a

I didn't say anything about the USB in a reflector.

> For the EZ-12 type reflector, the problem is mostly 2 dimensional.
> to reflector distance. So, 120 degrees would be 1/3 of a circle or:

120 degrees of reflector capturing the energy that was going the wrong way.
There is also the original energy headed in the right direction to begin
with.

> I'll throw together a 3D plot and demonstrate the difference between a
> biquad and a corner reflector. I'll also try to determine if the

The EZ-12 is not the corner reflector. The corner reflector on freeantennas
has a NEC model that looks even more like your biquad.

> I would call both of them 10dB based on all the various accuracies,

I would acll it 12 dB, because that's what I see with NetStumbler.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
Anonymous
September 25, 2005 6:50:28 AM

Archived from groups: (More info?)

On Sat, 24 Sep 2005 22:51:47 +0000 (UTC),
dold@XReXXusbXa.usenet.us.com wrote:

>I didn't say anything about the USB in a reflector.

Sorry. My fault.

>> For the EZ-12 type reflector, the problem is mostly 2 dimensional.
>> to reflector distance. So, 120 degrees would be 1/3 of a circle or:
>
>120 degrees of reflector capturing the energy that was going the wrong way.
>There is also the original energy headed in the right direction to begin
>with.

Yeah, but it's not headed directly to the target receiver. Pretend
the other end is a patch antenna about 1/2 wave across. At about 100
meters, that's:
tan (angle) = (6.5cm / 10,000cm)
angle = 0.05 degrees.
That's very small part of the RF that's "illuminating" the target
receiver. The rest of the signal from the vertical omni (dipole) is
going in all kinds of other directions, none of which end up at the
target receiver. Might as well ignore the contribution from the
"forward" wave directly from the omni.

>> I'll throw together a 3D plot and demonstrate the difference between a
>> biquad and a corner reflector. I'll also try to determine if the
>
>The EZ-12 is not the corner reflector. The corner reflector on freeantennas
>has a NEC model that looks even more like your biquad.

Sorry (again). I was too lazy to look at the web page.

Also, it's not my biquad. It's by Trevor Marshall. I just posted his
NEC2 model.

>> I would call both of them 10dB based on all the various accuracies,
>
>I would acll it 12 dB, because that's what I see with NetStumbler.

12dB over isotropic or over some reference antenna? Also, are you
sure you're not having reflection issues? I can move the antennas
around in my crude indoor test range to maximize the signal and end up
with about 3dB more gain than the calculations predict. Invariably,
it's the result of reflections. When I do the testing in a real range
or out in the open, the results tend to be more realistic.

Incidentally, remember that web page where someone compared the gain
of various types of home made antennas? They ended up with some
rather inconsistent results. Well, that was because they did it on
the pavement and were getting reflections. Foundit:
| http://martybugs.net/wireless/antennacomp.cgi

This looks interesting.
| http://pe2er.nl/antennetesten/antennameasurement.htm
I'll read it when I'm done fixing the washing machine.

Here's a biquad that claims 12-14dBi gain:
| http://nuke.freenet-antennas.com/modules.php?name=News&...
Note the external reflector. Nice idea.



--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice Skype: JeffLiebermann
# http://www.LearnByDestroying.com AE6KS
# http://802.11junk.com
# jeffl@comix.santa-cruz.ca.us
# jeffl@cruzio.com
Anonymous
September 25, 2005 6:52:17 AM

Archived from groups: (More info?)

On Sat, 24 Sep 2005 22:18:31 GMT, David Taylor <djtaylor@bigfoot.com>
wrote:

>> external coax connector. He could have done it without cramming the
>> whole mess into the tube. I personally don't find anything wonderful
>> about the arrangement.
>
>Nope nothing wonderful. The reason it was all in the tube was so that
>there was only one cable, the USB one coming out. Plenty of space in
>the rear of the pipe so loads of space for the radio. Easier to do that
>than to find another box to piggy back on to and the point of using the
>USB was to have as little RF loss in 15' of thin coax.
>David.

Well, that's fair. At first glance, it looked like the PCMCIA card
antenna was being used to feed the can antenna directly. I missed the
seperate driven element. Still not wonderful but good enough.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice Skype: JeffLiebermann
# http://www.LearnByDestroying.com AE6KS
# http://802.11junk.com
# jeffl@comix.santa-cruz.ca.us
# jeffl@cruzio.com
Anonymous
September 25, 2005 11:50:18 AM

Archived from groups: (More info?)

Jeff,

I pryed apart the cover on one of my Zonet ZEW2501 dongles.
Surprisingly, it didn't break but opened easily. Even the plastic tabs
stayed on so it looks like it may go back together again. I took some
pictures and posted them at:
http://www.patmedia.net/bseiler/zew2501.htm
There's a metal can on the front side (RF amp under it?) and a Zydas
chip on the back. I'm not sure where the antenna is. There's a short C
shaped trace on the front on the end opposite the usb connector. Is
that the antenna? There's an L shaped trace on the back right under
the C. Is that a ground plane? If you have time look at the photos,
I'd sure appreciate your best estimate on where to connect an external
antenna. Where should the center conductor go? Where should the braid
go? Should I cut any traces?

Here's a story to prove how new this RF stuff is to me:
In some of your earlier posts you referred to the antenna in a usb
dongle as a PIFA antenna. Each time I read that, I thought you meant
"Pain in the ..." antenna. Some recent googling informs me that it
really means Planar Inverted F Type antenna :) 

Thanks to all who are posting in this thread. I'm learning a lot.

Bruce
Anonymous
September 25, 2005 11:59:09 AM

Archived from groups: (More info?)

> seperate driven element. Still not wonderful but good enough.

You've hit the nail precisely there, "good enough" was the objective.
Quick to set up, easy to aim and with performance that was fit for
purpose, in this case the Travelodge to the internet connection. :) 

David.
Anonymous
September 25, 2005 12:43:41 PM

Archived from groups: (More info?)

On Sun, 25 Sep 2005 07:50:18 -0400, bjs555 <aaa@bbb.com> wrote:

>I pryed apart the cover on one of my Zonet ZEW2501 dongles.
>Surprisingly, it didn't break but opened easily. Even the plastic tabs
>stayed on so it looks like it may go back together again. I took some
>pictures and posted them at:
>http://www.patmedia.net/bseiler/zew2501.htm

Nice photos but a bit small. It's difficult for me to see what's
going on.

>There's a metal can on the front side (RF amp under it?)

No. Under the metal shield is the entire RF section except for the
antenna. The RF amplifier, if present, will be a tiny little chip.

>and a Zydas
>chip on the back. I'm not sure where the antenna is. There's a short C
>shaped trace on the front on the end opposite the usb connector. Is
>that the antenna? There's an L shaped trace on the back right under
>the C. Is that a ground plane?

The blue thing is the antenna.
http://www.gigaant.com/?id=535
The L shaped thing is a counterpoise which may or may not be grounded.
The thin trace coming from the shield can is the RF output. Remove
the can and see if there's a series capacitor on the trace where it
enters the can. If so, then you don't need to add one. The bad news
is that an RF connector or coax pigtail will need to added fairly
close to the shield can. I can't tell for sure because the photo is
so small and because there's a shadow to the left of the can just
where I need to get a better look.

>If you have time look at the photos,
>I'd sure appreciate your best estimate on where to connect an external
>antenna. Where should the center conductor go? Where should the braid
>go? Should I cut any traces?

My guess(tm) is to either.
1. Unsolder the blue antenna and attach there. Be sure to find a
nearby ground. There's probably one under the antenna but I can't
tell from here.
2. Cut the trace from the metal can to the antenna and attach a tiny
coax cable. Ground to the base of the shield can, not the cover.

>Here's a story to prove how new this RF stuff is to me:
>In some of your earlier posts you referred to the antenna in a usb
>dongle as a PIFA antenna. Each time I read that, I thought you meant
>"Pain in the ..." antenna. Some recent googling informs me that it
>really means Planar Inverted F Type antenna :) 

Well, the "F" is usually quite liberally interpreted. See:
http://www.ansoft.com/deliveringperformance/NSYSU2.pdf
for a rather larger variety of different PIFA styles.

>Thanks to all who are posting in this thread. I'm learning a lot.

You haven't destroyed anything yet. That's where the real learning
starts.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Anonymous
September 25, 2005 4:53:20 PM

Archived from groups: (More info?)

Thank you so much! I would never have guessed that the blue thing is
the antenna. I thought it was just a large capacitor.

On Sun, 25 Sep 2005 08:43:41 -0700, Jeff Liebermann
<jeffl@comix.santa-cruz.ca.us> wrote:

>The blue thing is the antenna.
> http://www.gigaant.com/?id=535
>The L shaped thing is a counterpoise which may or may not be grounded.
>The thin trace coming from the shield can is the RF output. Remove
>the can and see if there's a series capacitor on the trace where it
>enters the can. If so, then you don't need to add one. The bad news
>is that an RF connector or coax pigtail will need to added fairly
>close to the shield can. I can't tell for sure because the photo is
>so small and because there's a shadow to the left of the can just
>where I need to get a better look.
>
>>If you have time look at the photos,
>>I'd sure appreciate your best estimate on where to connect an external
>>antenna. Where should the center conductor go? Where should the braid
>>go? Should I cut any traces?
>
>My guess(tm) is to either.
>1. Unsolder the blue antenna and attach there. Be sure to find a
>nearby ground. There's probably one under the antenna but I can't
>tell from here.
>2. Cut the trace from the metal can to the antenna and attach a tiny
>coax cable. Ground to the base of the shield can, not the cover.
Anonymous
September 26, 2005 1:29:22 AM

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Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:

> Here's a biquad that claims 12-14dBi gain:
> | http://nuke.freenet-antennas.com/modules.php?name=News&...
> Note the external reflector. Nice idea.

That looks a lot like the Conifer 2400 that I have.

In a biquad, you said that you might try loops instead of squares, all that
matters is the length of the loop. That brings two questions to mind:

Isn't the spacing across the square important to the biquad? Isn't it a
phased array?

If the biquad were a biloop, would the elements be 124mm, or would they be
120mm, with 4 times 1mm left for the gap between the copper tube and the
center conductor?

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