Salad Bowl USB antenna

Yet another antenna abomination.

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's a stainless steel salad bowl, about 1 ft across.

I haven't done any real testing yet. It's sorta directional, shows some gain, and is cheap (about $9 in parts) to make.

Punch 1 3/8" dia hole in the bottom with a Greenlee or Walsco chassis punch. Do NOT try it with a rotary hole saw. It will grab and make a mess. Start with a 1/8" pilot hole. Enlarge to a 3/8" hole for the chassis punch. Then, use the 1 3/8" chassis punch.

In the hole, insert the 1" threaded to non-threaded PVC grey electrical adapters. Do NOT use the white PVC equivalents as they use a tapered, rather than straight, thread which is very difficult to crank tight. The washers are 1 1/2" to 1" reducing adapters. The flat bottom is a bit flimsy and should probably be reinforced with something (old CDROM disk?).

The center feed extension and handle are 1" PVC pipe. Any length will work. 3/4" pipe could have been used if the plastic case were removed from the USB device. However, 1" will work with other dongles.

The wireless USB dongle (or Wi-Spy) is connected to a USB extension cable and shoved into the pipe. Adjust the position so that it's close to the focus of the dish. It's NOT a parabola, so some trial and error will be needed. My current guess (probably wrong) puts the USB tip at 3" above the base.

A 1/2 wave (62mm) disk should probably be installed in front of the center pipe to block the direct path and to reflect some of the wasted RF back to the reflector. Next revision.

Reply to
Jeff Liebermann
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Thanks, Jeff for another educational post. You can check the focus of the dish visually since it's highly reflective - - just put a band of colored tape or mark a 1/2" wide colored ring with a felt tip pen on the end of the tubing and position your eyeball about 20 ft away while someone moves the tubing in or out until you see the widest area of that color reflected in the dish - - your 3" is probably pretty close.

Chuck

Reply to
Chuck Olson

"Chuck Olson" hath wroth:

Good idea. I'll try that later tonight (paying work cometh first).

The way I tried it was to temporarily remove the center (white) PVC pipe and use my mini-maglite flashlight, with the reflector removed. It simulates a hemispherical illuminator pattern similar to the typical USB dongle. The pattern of light on the wall was interesting. There was some semblence of a focused beam in the correct direction. However, the steep sides of the bowl caused an annular ring to appear to the sides. The bowl has some nasty side lobes. Ideally, the dish should be more parabolic. However the lack of a controlled feed illumination pattern from the USB dongle makes almost any style of reflector a problem. I suspect a simple corner reflector, the same size as the salad bowl, would do better.

Reply to
Jeff Liebermann

A non-modeled abomination from Jeff?

Speaketh thou from experience? tossed your salad? ;-)

[...]

You should be able to tell by taking the top off a mini-maglite (lantern mode), and sliding that to the end of the pipe, and then illuminating the widest band in the bowl.

That would add another tunable element. The dongle would be inside the pipe, about 31mm from the disk, and the disk positioned 31mm past the focal point discovered earlier.

Reply to
dold

I didn't even try. I know garbage when I build it. Still, the basic design has some merits. If not a salad bowl, perhaps a wok, colander, or snow saucer? Eventually, I'll do a model although I know it will be horrible.

The real problem is the hemispherical pattern of the USB wireless dongle. It radiates in all directions roughly equally. The high f/D ratio deep dish is idea for such a feed, but there's still approximately half the power that radiates from the dongle that doesn't hit the reflector. I figure an efficiency of no better than

25% with the current kludge.

Yeah. The first problem was that I my drill press didn't have sufficient reach to drill the center hole. So, I bought a genuine ACE Hardware 1 3/8" hole saw (made for metal) and guide drill for $19 (ouch). I stuffed it into my Milwaukee Hole Hawg, put a 4x4 under it, and proceeded to try and drill a hole. Any semblance to a safety hazard is purely coincidental. Instead of a hole, I managed to rip an ugly gouge with very sharp and rough edges. I spent some time doing the blacksmith routine on the salad bowl but eventually gave up. I went to the hardware store, bought another salad bowl, borrowed a proper 1 3/8" chassis punch from a machine shop, and punched the hole quite easily.

I did that. See my other post in this thread. I can't do it with the PVC pipe attached because it's not optically transparent. So, I just removed it and waved it around the general area. The result was odd. I had something resembling a focused blob on the wall, which means it's somewhat of a parabola. However, I also had an annular ring from reflections off the steep vertical sides of the bowl. This dish is gonna have one hell of a side lobe problem.

Yep. That what I was going to try first. My guess is that the 1/2 wave (62mm) diameter reflector will need to be considerably closer to the USB dongle than 1/4 wave. Something like this:

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with a dish instead of a flat plate reflector.

Reply to
Jeff Liebermann

Jeff,

where is the dongle located ? would it help if the dongle was held out in front of some type of refector such as in the Primestar wi fi dish antenna setup ?

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Jeff Liebermann wrote:

Reply to
frankdowling1

Shoved up the center tube from the back of the salad bowl.

I don't think so. A reflector of some sorts needs to be installed in front. However, if it were a can, the illumination angle would be perhaps 60 degress, which would be insufficient to illuminate the entire dish. Also, because the focus is only about 3" from the base, there's no room for a proper can (waveguide) feed.

Reply to
Jeff Liebermann

If you use a wok, you'll then be required to post your pic on the New Zealand site, which is filled with unmodeled abominations, some of which, one would think, _can't_ work, like the tuna fish can. ;-)

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They really enjoy the wok reflectors. You've added a good tuning mechanism and a much sturdier support.

They have soft clamps held by c-clamps at the edge of the dish, poking in the right general vicinity.

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And they claim to have found a wok that is parabolic. That one has a sturdier mount through the back.

The other post wasn't there when I started typing, and I saw it as soon as I finished posting ;-(

I was thinking of the maglite tip sticking out the end of the PVC a little, just to find the proper depth, and then readjusting the PVC to cover the spot you had just identified.

Now here's an application for me:

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Reply to
dold

There is a break even point where you are better off just buying an old dish. I got two dishes for about $50 with shipping on ebay. I'm sure if you had connections, the price would be free.

Jeff Liebermann wrote:

Reply to
miso

There's a house near here that has a PrimeStar dish on the side of the house. The feedhorn is gone, but the dish is still there. Not sure why. Since PrimeStar is long since gone, most of the dishes are on rooftops because of lack of effort on the part of the occupant.

Those are larger and bulkier that Jeff's salad bowl, though. The salad bowl probably cost $3.49.

Reply to
dold

Now that's a big salad. Given a yound niece of mine, I can understand why you might have such a bowl laying around unused. She (age 3) won't eat veggies for anything.

Cool, thanks for the idea.

fundamentalism, fundamentally wrong.

Reply to
Rico

The Primestar dishes are good for wifi. I've seen dishes with no connection on homes too. I've never bothered to knock on a door and offer to remove one, but that would be a plan if you want to do it on the cheap.

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found this old Starband on a hill in the Nevada desert. I suppose I could have relieved them of it, but who knows if it is some project in the works. In any event, the dishes are pretty cheap on the used market. This particular site had microflects on it, so maybe the starband as a poor mans reflector. images/ttr/brock/reflectors.jpg

I've built some biquad antennas. Quite a bang for the buck, and very simple.

snipped-for-privacy@XReXXSalad.usenet.us.com wrote:

Reply to
miso

snipped-for-privacy@sushi.com hath wroth:

Methinks I forgot to mention why I used a salad bowl and plastic pipe instead of similar sized dish, such as an 18" pizza dish. The idea was to provide some gain and directionality for a USB dongle or Wi-Spy spectrum analyzer without butchering the dongle by adding a pigail or SMA connector.

The problem is that the USB dongles antenna pattern is roughly hemispherical (equal signal strength in all directions). With a fairly flat (small f/D ratio) dish, such as an 18" DBS dish, only a small part of the RF coming from the USB adapter hits the dish and is reflected in the desired direction. The rest goes off in useless directions. I worked out the numbers in a previous posting to alt.internet.wireless, but am too lazy to find it again.

The deep dish salad bowl is slightly better. My guess is about 40% of the RF coming from the USB dongle hits the dish. With an added reflector in front of the USB dongle, this might be improved to perhaps 50%. Not bad for $9 in parts and only one big hole to drill.

The right way to do this would be to attach a connector or pigtail to the USB dongle and build a proper antenna. However, I wasn't looking for the right way, just the cheapest and easiest.

Primestar dish with a Pacific Wireless feed:

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Yet another nice biquad construction article:
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Dish with biquad feed:
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Reply to
Jeff Liebermann

Greetings form sunny New Zealand! Yes- guilty as charged with our WokFi ideas at =>

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. These arose 2004 as a student project & have since been outstandingly well received ( site has ~ 3/4 million visitors at ~ 1000 daily), with numerous global success stories. We highly recommend the ~15dB boutique version for both function & form =>
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, BUT the ~ 9dB "bendy plastic" appraach =>
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is a breeze to organise & costs peanuts. Stainless steel salad bowls are better used for culinary purposes!

In all cases it's almost ESSENTIAL to use Netstumbler on a laptop ( or WiFoFoFum on a WiFi PDA) to do a signal audit & allow anntena tweaking & "sweet spot" positioning.

A key part of the project was to allow WiFi to be used in "$1 a day" countries - hence the POORMAN title. Stan

Reply to
stan.swan

snipped-for-privacy@gmail.com hath wroth:

Nicely done. I'm probably one of those visitors. As you seem to have a monopoly on antennas made from cooking utensils, I made sure I wasn't copying one of your ideas.

Ah, but the salad bowl construction includes a handle and USB mounting contrivance in the basic design. Although the gain is probably less than your boutique vegetable washer version, the construction is much simpler and does not require cannibalizing a desk lamp for a mounting. I'll do some gain measurements when it stops raining.

Agreed. For the salad bowl design, the primary purpose was to provide some added gain and directionality for the Wi-Spy spectrum analyzer.

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has a built in level meter with a much faster response than Netstumbler. However, I'm not so certain that either the USB dongle of the converted wireless mouse receiver used in Wi-Spy are anywhere near accurate. They both convert a 0-255 RSSI count to dBm using some manner of lookup table. I'll try to make some measurements and see what happens.

Well, if cheap is what you want, permit me to suggest a slight modification. Cease looking for a parbolic dish and just use a flat plate reflector. The difference in gain between a parabola and flat plate of identical size in quite small. The arguement over the Hawking small dish antenna gain versus a flat disk reflector resulted in some calcs at:

Hawking Dish |

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Same thing with flat plate reflector: |
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7.7dBi for the dish. 8.3dBi for the flat plate. With small antennas (i.e. reflectors about 1 wavelength diameter), a flat plate actually has slightly more gain than a dish.
Reply to
Jeff Liebermann

I love the experiment and go site, with so many possibilities and attempts. Some are a little goofy, like the tuna can, but the CD cover is new to me... which gives rise to my only complaint with the site.

The opening page has little tiny jpg images that I can't resolve, and clicking through each is tedious, unless I realize that one of them is new. The btique is a perfect example. That is cute, but there's no reference to the building details, although I recall having seen them on an earlier browse through the images.

Are the images arranged by date? Why isn't there at least a comment for each one? Why did you chose jpg images instead of pages with text and images?

That CDROM cover seems pitched at less than a 90 degree angle. Is there experimental detail on that? If I make one of those, I would be inclined to have a fold-down flap with the FP noted, and cut at the right shape to mark the proper opening angle.

Reply to
dold

Yes- apologies re the tiny .jpgs etc on

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. The site just evolved from our "work in progress/lab notes", & was originally intended just to keep class members attuned to each others efforts. We'd considered a total revamp, & may well yet do so, but significant issue were 1. Hosting - presently still with a free NZ host (Orcon), which gives super fast access within NZ . Now many mirrors of course 2. Appreciation of non English speaking/reading users 3. Appreciation of VERY basic PC gear in many "$1 a day" countries precluding media rich info.

Asian scoops are in fact usually cheaper than a similar Aluminium/Stainless bowl or metal sheet in many countries, & certainly offer less wind resistance. They're neater too of course, & their use I confess appealed greatly to our Kiwi sense of humour! Stan

Reply to
stan.swan

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