Archived from groups: alt.internet.wireless (
More info?)
On Mon, 5 Jul 2004 01:03:14 +0000 (UTC), dold@ExternalXa.usenet.us.com
wrote:
>There was a picture on one of the .nz web pages,
I think you mean this one.
http://www.usbwifi.orcon.net.nz/usbscoop.jpg
A little reminder... the efficiency of a parbolic reflector is at best
50% assuming a decent feed that doesn't over or under illuminate the
dish. My guess(tm) is that the efficiency of a ceramic patch antenna,
illuminating a chrome plated steel vegetable scoop is close to 10%.
Chrome also makes a lousy RF conductor.
>The top portion of the jpeg-as-web-page shows the naked dongle on a
>broomstick above the roof.
Swell. Tear apart the USB radio, remove the ceramic patch antenna,
and replace it with a coax connector or solder on pigtail. Attach a
real antenna. See:
http://jeffl.ihwy.com/linksys/wusb11/wusb11-2.jpg
The pads in the upper right are where the ceramic patch antenna was
connected. The pattern is perfect for a PC mount SMA connector.
However, I got lazy and soldered some semi-rigid coax to the pads,
with an SMA at the end.
>> At RF frequencies, ALL the RF conductivity is on the surface of the
>> conductor. You could make it out of a silver plated plastic insulator
>I recall skin effect from my days in heavy radar, but I don't know if this
>is the proper skin. Silver plated anything is a little on the pricey side
>for the homebrew antenna market.
Not really. I make my antenna parts for copper water pipe, copper
flashing, and sheet brass. Mostly, I use electroless silver solution
(silver cyanide) to plate the copper and brass. The problem with
electroless silver is that it's not really thick enough at the lower
ham frequencies. I have the calcs if you want them. However, for
2.4Ghz, it's not problem. One skin depth is:
The skin depth is:
depth = 2.6 * K1 / sqrt(freq)
where:
Depth = inches
Freq = Hz
K1 = 0.94 for silver
depth = 2.6 * 0.94 / 49000 = 0.000026 in = 26 micro inches.
(or about 0.3 microns).
Electroless silver is self limiting at 2-3 microns, so this should be
no problem at 2.4GHz where anything over 0.3 microns will suffice. If
you don't mind making a mess, silver plating is fairly easy. The
biggest headache was getting the chemicals shipped to me without a
hazardous substance waver.
Some useful instructions on plating:
http://www.LearnByDestroying.com/crud/silver-plating.txt
http://www.qsl.net/n9zia/why_silver_plate.html
More on skin effect:
http://www.geocities.com/CapeCanaveral/Hangar/6160/skineffect.html
>David Taylor speaks of putting a horn on the end of a can.
Bah humbug. I was thinking of something more substantial.
http://www.setileague.org/photos/wghorn/ewen2001.jpg (1420MHz)
http://www.setileague.org/photos/wghorn.htm
http://www.barc.org/ao40_antennas/rxantenna.html
>> No. DC conductivity does NOT equate to RF conductivity. RF
>> conductivity is all skin effect and is on the surface of the
>> conductor. Some skin effect references:
>That's in a material that is conductive. I don't know that
>the liner in these cardboard tins is conductive, or all the same.
Neither do I. However, even if they are conductive at DC (as measured
by an ohms-guesser), it's still the surface conductivity and skin
effect that determines the performance at 2.4GHz. One of my better
screwups was instead of painting an aluminium antenna, I cleverly had
it black anodized. Performance stunk until I scraped off the plating
with sandpaper. The same problem occurrs with chrome, and zinc
plating.
>I really am interested in the USB dongle. It's so much cheaper than the
>802.11b card+pigtail+cantenna. The guys in nz suggest pulling the ceramic
>patch off and soldering on a different antenna, but then you've destroyed
>the dongle, and need to adhere to stricter design for radiator sizing.
Sacrifices must be made. Use the force (or a suitable disassembly
tool).
--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558