On Sun, 06 Sep 2009 16:21:54 -0300, Freeballer <none@isp.com> wrote:
>cable is roughly 6-8ft long now. I was thinking it may help signal to
>shorten to pigtail size and use a usb extension cable instead.
Good idea. USB cables offer no RF loss. The official limit for USB
2.0 is 5 meters, but I've gone furthur without problems. There are
also low loss cables, USB hubs, and absurdly long USB extension cables
that will work for longer distances. The catch is that the USB device
will now be outdoors, and should be protected against the weather.
>I've so wanted to get a cantenna but I'm worried of screwing it up and
>scrapping the project.
Do it anyway. There are plenty of plans online. Anything is better
than the stock rubber ducky. I prefer something better, but if your
requirements are minimal, it should constitute an improvement.
>The usb wireless contraption DOES have a rp-sma
>connector and came with an antenna that looks like this:
>http://www.fab-corp.com/files/t_16186_04.jpg
>
>I wanted a crimper for a bit. I think I'll get a cheapo for now.
About $25 or less each. Prices are all over the place.
>I have
>a coax stripper (rg6) that swivels around the cable but I need to say if
>I can adjust the diameter, if I cannot than an exacto is good idea
That style of cable stripper will work well for 0.25" diameter cables
and larger. The 0.100" dia cable (LMR100, RG316/u) that is used with
SMA connectors is too floppy to be stripped that way. I use a thermal
stripper:
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320419409416>
However, I use rounded stripper blades. If you're going to work with
tiny cables, PTFE insulation, or have no luck with a razor blade, this
is what you want.
>when you say 8dbi gain does that mean from the normal 4db antenna?
>(cantenna)
No. The "i" means over an isotropic reference, which is a mythical
antenna, with a sperical pattern, and a gain of zero. This is the
most common reference found when designing and specifying antennas.
There's also dBd, which is dB over a dipole, which has a gain of
2.15dBi.
My guess is the rubber ducky antenna has a specified gain of 4dBi
which is about what you would get with a 7" long colinear antenna. The
cantenna might have a gain of about 8dBi. Therefore, your net
improvement from the rubber ducky to the cantenna is 4dB. In terms of
range improvement, that's about 1.6 times. (6dB is twice, 12dB is 4
times, etc).
>thank you for the link to the yugi. thats cheapest I've seen them so
>maybee that'll be something to try later.
The MFJ yagi is junk but can be made to work. A friend used one on a
local tower that was in the coastal fog belt. The copper folded
dipole driven element corroded through in about 6 months. Replaced it
with a $70 panel antenna, which has lasted now about 5 years.
Incidentally, you can sometimes find MFJunk from other vendors
cheaper:
<http://www.rlham.com/cgi-bin/shop/modellookup.dbw?MODEL=MFJ1800>
>How about the wi-fire?
>Has anybody tried one? http://www.hfield.com/the-wi-fire/
The tech specs are lacking. It's just an ordinary USB wi-fi adapter
that belches +27dBm (500mw) of xmit power. That's quite a bit of
power for a USB device. However, unless it's matched by a similar
increase in xmit power at the access point, the added power is
worthless. The result of high power is an "alligator" which is an
animal with a big mouth and small ears. Everyone can hear this thing
transmit, but it can't hear the relatively low power replies. See if
you can find the FCC ID number, and look it up on the FCC ID pages to
see what's inside.
>it says it'll extend your distance by 1000, and the author of an
>engadget article said it was pretty good. but didn't compare it to other
>solutions like yugi, cantenna, bi-directional, etc...
Baloney. They also don't specify what they're comparing it with that
would produce a x1000 increase in range. Let's assume it's a fairly
disgusting MiniPCI card, with an insipid internal antenna in a laptop,
with an effective radiated power of 10dBm. That's the usual +13dBm
xmitter and +2dBi antenna, minus 2dB of coax loss. In order to obtain
a 1000x increase in range, the combination of antenna gain and tx
power would need to provide a 30dB gain increase. Assuming the same
style antenna (based on similar size antenns), the xmitter would need
to belch +13dBm + 30dB = 43dBm which is 20 watts of xmit power. I
don't think so. I really doubt the USB dongle has a much more gain
than the average internal laptop antenna, but if you attach the
biggest external dish antenna that's commonly available, which has a
gain of +24dBi, the resultant tx power required to get a x1000 range
improvement is +13dBm + 30dB -24dBi = +19dBm or about 80mw. That's
entirely possible but the antenna is about 3ft across, which doesn't
quite fit inside the USB dongle.
The above calcs may seem a bit confusing, but if you read through the
technobabble one line at a time, and use an online calculator:
<http://www.terabeam.com/support/calculations/watts-dbm.php>
to convert from dBm to milliwatts and back, it should be fairly clear.
--
Jeff Liebermann
jeffl@cruzio.com
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
crimping new rp-sma / cantenna / yugi? 
Linear Mode
