[clue-tech] Practical D.I.Y. WiFi antenna info?

[Bruce Ediger]

Thanks for the reply!

On Wed, 14 Jul 2010, Nate Duehr wrote:

> ACTUALLY tuned to the 2.4 GHz band, is very very questionable.  You're
> also talking millimeters of difference between getting that antenna
> "right" and getting it "wrong".  A couple millimeters either way on
> those coils, or the wrong size on them, and who knows if your antenna is
> a proper 50 Ohm load to the transmitter, and/or whether or not it's
> really on-frequency.

That was just the simplest (and one of the cooler-looking) antennas I could
find that had dimensions and pictures attached that I could do last night
with what was in the house after the kids fell asleep.

So, I really do need to use copper wire to get the measurements and bends
right, and also for the malleablity to fiddle with it: coathanger wire was
all I had at 10:30pm, and it's way to thick and stiff.  I wasn't off 5mm
from the article, but I was off 2mm one way or the other.

>> 1. Do you have to use hard-to-get LMR-400 coax, or does other coax work too?
>
> The issue at microwave frequencies is loss.  LMR-400 is the BOTTOM of my
> quality level list for 2 GHz microwaves... even then, keeping the run of
> coax as insanely short as possible, and using quality connectors is
> required.

So, "yes, you have to use LMR-400 or better."  I'd only want to use 2-3 feet
of it.

>> 2. Do you have to use ridiculously expensive N-type connectors, or can you
>> use BNC or other connectors?
>>
> BNC are pretty good at 2.4 GHz.  N are expensive, but they tend to be
> very low loss (if you buy from a reputable brand name... there are TONS
> of cheap Chinese knock-offs with cheap nickel plating, etc.)... Amphenol
> is my brand of choice on almost all connectors.  Andrews also.

Good advice.  BNC run $2.50 at Radio Shack, whereas N-type is $4.50 in
volume off the internet, and apparently not even available in Denver,
although I'm scared to go into Fistell's.

>> 3. When I'm trying things out, do I really need to solder an RF jack on the
>> PCMCIA card, use an expensive pigtail, etc, or can I just jerry-rig it with
>> alligator clips and stuff?
>>
> Alligator clips are way too lossy at 2.4 GHz and introduce Impedance
> "bumps" that will throw off the tuning/happiness of the transmitter.  At
> these power levels, you won't damage anything, but it won't perform
> worth a damn.

So beyond the shape of the coathanger wire antenna, I probably introduced
all kinds of loss.

> What are you trying to accomplish.  Does this laptop/PCMCIA card
> application need to connect to an AP that's 100 feet away, 1000, 10,000?

100 feet max, for now.  I'd like to try some of the more directional antennas
at a later date, just to see what's floating around in the air in my
neighborhood.

> you... but I'm a little worried that if your budget is tight enough that
> an N-connector is too expensive, ruining a few with the soldering iron
> probably isn't the best way to spend your money...

My budget isn't *that* tight, but my sense of proportion prevents me from
spending $50 on cabling for a $10 computer.  Another $10, plus $2.50 for
a connector now and then, I can accept emotionally.  Some of the N-type
connectors had prices in the 10s of dollars.

> Life's too short to screw around with microwave antennas.  Unless you
> REALLY like it, or you're REALLY bored. Or unless the point is to
> learn...  ;-)

My point is to learn.  I've never really messed around with laptops and
wireless, except to keep my wife and her Mac happy, and that's just Cargo
Cult configuration.