NetStumbler.com Forums - Post Your Homebrew Antennas = Here

From: Subject: NetStumbler.com Forums - Post Your Homebrew Antennas Here Date: Thu, 1 Aug 2002 12:39:25 -0700 MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_NextPart_000_0064_01C23958.783F6100"; type="text/html" X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 This is a multi-part message in MIME format. ------=_NextPart_000_0064_01C23958.783F6100 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Content-Location: http://forums.netstumbler.com/showthread.php?s=&threadid=2034&perpage=40&pagenumber=5 NetStumbler.com Forums - Post Your Homebrew Antennas = Here

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NetStumbler.com=20 Forums > Wireless=20 Forums > Hardware=20 > Post Your Homebrew Antennas = Here

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Author

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bmoore314
Mini=20 Stumbler
3D""=20

Registered: Jun=20 2002
Location: south bay area, california
Posts: = 19

Nice antenna=20 there lincomatic, maybe I'm gonna have to try that = design=20 next. It looked really difficult from the guerilla.net = instructions, so I stayed away from it. Your page = makes it=20 look easy. I am guessing the reason you signal = strength was=20 fluctuation so much was from excess noise, and such. = With a=20 larger antenna, especially an omni, you amplify the = noise as=20 well as the signal. My waveguide with a collector was = pretty=20 erratic during the day, and solid during the night. My = new=20 dish one gives a strong signal during the day, and = even=20 stronger at night. Probably due to the narrow = beamwidth of a=20 dish, blocks out more noise than just a plain = waveguide. Just=20 my $0.02

Brian

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07-22-2002 04:51=20 PM

=20 =

lincomatic
Squaawwkkk!

Registered: Apr=20 2002
Location: Congo
Posts: 1062

i = hope i made=20 it a bit more understandable. I was kind of skeptical = of the=20 design at first, and it looked like a lot of work to = build,=20 but seeing that it matched the Lucent/Maxrad convinced = me that=20 it was a good design.

I didn't have any screws = handy to=20 aid in winding the coils...man my fingers still hurt! = some=20 people have suggested building a jig by driving the = screw into=20 a block of wood and drilling a small hole into the = wood beside=20 it to catch the wire. it still takes hours to build = compared=20 to my other antennae which were pretty easy & = fast. but i=20 am pretty impressed w/ the results.

as for the = signal=20 fluctuation, i often get that during the day. it was=20 fluctuating with both the built-in antenna and the = omni.=20 usually i get the most stable readings late at nite = when it's=20 cool like after 2am.

stupid me...left the omni = out on=20 my deck to bake the epoxy in the sun...the wind blew = it off=20 and it fell to the ground 40ft below and completely = fell=20 apart. argh! had to spend over 1/2 hr reassembling it = after=20 that.

__________________
~lincomatic

Last edited by=20 lincomatic on 07-23-2002 at 09:46 PM

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07-22-2002 04:59=20 PM

=20 =

sparafina
semiotech

Registered: May=20 2002
Location: AUS/LAX/DCA
Posts: = 223

Re: = collinear omni=20 rocks=20

quote:
Originally posted by lincomatic
I = finally=20 built the gnet low power collinear. Took forever, = but it's=20 done, and it works great. full story:

http://www.geocities.com/lincomatic/collinear.html
I'm=20 going to try closing my sunroof onto it and = stumbling with=20 it when i run some errands today.

Way cool page, much better than = the=20 original instructions. Have sent you the g.net = archives I=20 have.

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07-23-2002 02:17=20 PM

=20 =

lincomatic
Squaawwkkk!

Registered: Apr=20 2002
Location: Congo
Posts: 1062

for anyone=20 who wants to do antenna modeling with = NEC2,
here is=20 a great tutorial:

http://www.antennex.com/w4rnl/

__________________
~lincomatic

Last edited by=20 lincomatic on 07-25-2002 at 10:48 PM

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07-23-2002 02:49=20 PM

=20 =

norm
Mini = Stumbler

Registered: May=20 2002
Location: UK
Posts: 19

will you=20 consider building a WaveGuide next Linomatic, it looks = a=20 really clean/efficient design

3D""=20

http://www.narx.net/~mike/projects/waveguide/<= /P>

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07-23-2002 09:07=20 PM

=20 =

lincomatic
Squaawwkkk!

Registered: Apr=20 2002
Location: Congo
Posts: 1062

norm,

yes, slotted waveguides are very = cool.=20 trevor marshall has a design too:

http://trevormarshall.com/waveguides.htm

but=20 it will probably be a while before i build one of = these=20 because:
1) it doesn't fit my idea of cheap (that = mike guy=20 spent $250!) and here i was moaning about the = collinear=20 costing me $11 ... i have yet to find a good source = for the=20 extrusions...
2) the thing is huge! i don't really = have a=20 use for such a beast at the moment.

but the = coolness=20 factor beckons...don't tempt me 3D""=20

i'm going to at least wait until=20 sparafina builds his first. 3D""=20

__________________
~lincomatic

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07-23-2002 09:45=20 PM

=20 =

norm
Mini = Stumbler

Registered: May=20 2002
Location: UK
Posts: 19

i = think that=20 may have been $250 (Austrailian dollars) which works = out as=20 about $135 US

need to find a place to machine = it for a=20 similar price now 3D""=20

i like your collinear article = btw.

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07-23-2002 09:56=20 PM

=20 =

lincomatic
Squaawwkkk!

Registered: Apr=20 2002
Location: Congo
Posts: 1062

quote:
Originally posted by norm
i think that = may=20 have been $250 (Austrailian dollars) which works out = as=20 about $135 US

need to find a place to machine = it for=20 a similar price now

i like your collinear article = btw.

if you can get an affordable = source for=20 the extrusion (some guys bought them for $USD35-50, = you can=20 save a lot of $$ by cutting the slots yourself. trevor = marshall just used hand tools on his.

glad you = found my=20 collinear article useful. it's been such a big chore = digging=20 up info from the internet on building 2.4GHz = antennae....i'm=20 trying to build up a repository of info now. seems = like sites=20 are disappearing all the time.

__________________
~lincomatic

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07-23-2002 10:04=20 PM

=20 =

sparafina
semiotech

Registered: May=20 2002
Location: AUS/LAX/DCA
Posts: = 223

quote:
Originally posted by lincomatic
yes, = slotted=20 waveguides are very cool.
i'm going to at least = wait=20 until sparafina builds his first.

I'm still looking around for = usable=20 aluminum extrusion, I need to pay a visit to the local = junk=20 yards for car parts anyway. 3D""=20

I'm thinking of using foil covered = foam core=20 for a prototype, a la Christoph Catelain's (http://users.skynet.be/chricat/BT.html)=20 experiments (see bottom of page). I'll try an meet up = with him=20 in September, need to brush up on my technical = french.

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07-24-2002 06:17=20 AM

=20 =

lincomatic
Squaawwkkk!

Registered: Apr=20 2002
Location: Congo
Posts: 1062

quote:
Originally posted by sparafina
I'm = thinking of=20 using foil covered foam core for a prototype, a la = Christoph=20 Catelain's (http://users.skynet.be/chricat/BT.html)=20 experiments (see bottom of page). I'll try an meet = up with=20 him in September, need to brush up on my technical = french.=20

that's a great idea! or how about = foil-covered corrugated cardboard? maybe we can sell = them on=20 ebay! 3D""=20

have u made contact w/ Christoph = Catelain?=20 that would be cool to meet him ... he must have a lot = of=20 knowledge from all that experimenting he's = done.

__________________
~lincomatic

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07-24-2002 09:00=20 AM

=20 =

sparafina
semiotech

Registered: May=20 2002
Location: AUS/LAX/DCA
Posts: = 223

got motivated=20 and did some lateral thinking after reading the herf = and=20 microwave threads.

these links are archives = from=20 homepower magazine for building a microwave leakage = detector.=20 The scanned diagram is crap, but a good tease. Will = need to=20 find a dead tree edition if possible.

http://www.ibiblio.org/pub/academic/environment/alternati= ve-energy/energy-resources/homepower-magazine/archives/35/35p68.txt
http://www.ibiblio.org/pub/academic/environment/alternati= ve-energy/energy-resources/homepower-magazine/archives/35/35p72.gif
http://www.ibiblio.org/pub/academic/environment/alternati= ve-energy/energy-resources/homepower-magazine/archives/35/35p72.txt
here's=20 the interesting stuff from the first = article:

Some=20 Technical Notes About Microwaves and Their=20 Measurement
Microwaves are a non-ionizing radiation = comprising part of the
electromagnetic spectrum = from about=20 0.3 GHz to 300 GHz. GHz
stands for gigahertz or = one=20 billion vibrations per second. All
electromagnetic = waves=20 travel through free space at a speed of
about 300 = million=20 meters per second. The length of any given
wave in = space=20 (LAMBDA) is the speed of propagation divided by =
its=20 frequency (=9F),
Or: LAMBDA =3D 30/=9F
=9F =3D = 30/ LAMBDA
for=20 wavelengths in centimeters and frequency in = gigahertz
For a=20 microwave oven:
=9F =3D 2.45 GHz, LAMBDA =3D = 30/=9F, LAMBDA =3D=20 30/2.45, LAMBDA =3D
12.24 cm or 4.82 = inches
Microwave=20 power is measured in units, and in units per area =
space.=20 For example, a typical microwave oven will generate =
about=20 700 total watts of power and the leakage, measured 5 = cm=20
from the unit might be 0.1 milliwatt per square = centimeter=20
(cm2), or 100 microwatts per cm2. One milliwatt = =3D 1/1000=20
watt and microwatt =3D 1/1,000,000 watt. Ideally = microwaves=20
radiate from a source in spherical waves the power = density=20 of
which is proportional to the inverse square of = the=20 distance to
the source. If the distance is doubled = (D =3D 2)=20 power is 1/2^2 or
X1/4. If the distance is halved, = (D =3D=20 0.5) power is 1/(0.5)^2 or
X4. Power measurements = made=20 within one wavelength or so of a
source (near = field) will=20 exhibit irregularities due to power
storage and = exchange=20 in the elements of the radiating part.
The natural=20 microwave power level
It is challenging to compare = a single=20 frequency modulated
signal such as a microwave = oven=20 leakage to the complex sum of
microwave power = exposure=20 from nature. For this article I have
assumed that = the=20 power of natural microwave radiation at 2.45
GHz = can be=20 estimated as a an audio bandwidth modulation of =
290=F8K [THE=20 POWER OF NATURAL MICROWAVE RADIATION AT 2.45
GHZ = CAN BE=20 ESTIMATED AS] an audio bandwidth modulation of =
290=F8K=20 microwave noise centered on 2.45 GHz is analogous. = This=20
may or may not be true. Natural microwave noise = power =3D PN=20 =3D
kTB where:
PN =3D noise power (watts)
k = =3D=20 Boltzmann's constant (J/K)
B =3D bandwidth = (Hz)
T =3D=20 temperature (K)
Given T =3D 290=F8K, B =3D 20 kHz, = PN =3D 8 x 10-17=20 watts.
The "Cantanna" is a circular waveguide to = coaxial=20 transition
with a point contact diode mounted as a = shunt=20 element. The
extended wire serves as an E = (electrostatic)=20 field probe. For the
TEll mode the circular guide = exhibits=20 cutoff at a wavelength
equal to 1.7 times the = diameter.=20 The next mode will exist at 1.3
times the = diameter. The=20 coffee can is optimized for frequencies
near 2.45 = GHz but=20 is sensitive to others as well. It has a =
polarization axis=20 parallel to the E field probe and should be =
rotated during=20 measurement for the strongest detected = signal.

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07-24-2002 09:23=20 AM

=20 =

lincomatic
Squaawwkkk!

Registered: Apr=20 2002
Location: Congo
Posts: 1062

cool. that=20 looks like a low-cost version of trevor marshall's = microwave=20 detector he demoed @ the first SocalWUG = meeting.

__________________
~lincomatic

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07-24-2002 09:28=20 AM

=20 =

sparafina
semiotech

Registered: May=20 2002
Location: AUS/LAX/DCA
Posts: = 223

quote:
Originally posted by lincomatic =

that's=20 a great idea! or how about foil-covered corrugated=20 cardboard? maybe we can sell them on ebay!

have u made contact w/ Christoph = Catelain?=20 that would be cool to meet him ... he must have a = lot of=20 knowledge from all that experimenting he's done. =

I live in fairly humid area, so = I've=20 ruled out carboard. I need to stick the foam core into = the=20 microwave and see if it absorbs the waves, the foil = should be=20 fine but the slots may need to be covered.. Another = thought is=20 the foil covered sheathing they put on new housing=20 construction, a trip to the construction dumpster is = in=20 order.

I'd love to sell cantennas on ebay, = spray paint=20 them olive drab with flat black print to make them = look=20 surplus, but that's an awful lot of beans to eat. 3D""=20

Actually a light weight slotted = waveguide=20 built with foamcore and reinforced with fiberglass or = monoque=20 would be pretty cool.

I just bought the ticket = to=20 Amsterdam, so I'll email Christof and see if we can = meet for a=20 beer in Liege.

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07-24-2002 09:54=20 AM

=20 =

lincomatic
Squaawwkkk!

Registered: Apr=20 2002
Location: Congo
Posts: 1062

my roof has=20 this rigid foam insulation sandwiched in aluminum = sheeting on=20 both sides. wonder if it would be good for a = waveguide. next=20 time i'm at home despot i'll pick some up. maybe i'll = be=20 making a waveguide after all 3D""=20

__________________
~lincomatic

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07-24-2002 10:12=20 AM

=20 =

sparafina
semiotech

Registered: May=20 2002
Location: AUS/LAX/DCA
Posts: = 223

quote:
Originally posted by lincomatic
my = roof has=20 this rigid foam insulation sandwiched in aluminum = sheeting=20 on both sides. wonder if it would be good for a = waveguide.=20 next time i'm at home despot i'll pick some up. = maybe i'll=20 be making a waveguide after all

that's the stuff I'm thinking of. = BTW, on=20 trevor marshall site the plans for the 16 slot are = also=20 available, but not linked. You can get it = here:

www.trevormarshall.com/wave16.zip

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07-24-2002 11:11=20 AM

=20 =

lincomatic
Squaawwkkk!

Registered: Apr=20 2002
Location: Congo
Posts: 1062

thanks for=20 the link. man, inside dimensional tolerance 0.5%. = that's going=20 to be tough with foam since it's so floppy. i wonder = how=20 critical the outside dimension is, or if it even = matters. i=20 like your fiberglass ideas...thinking of some groovy = paint=20 jobs like on surfboards...antennas don't have to be = ugly=20 anymore 3D""=20

__________________
~lincomatic

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07-24-2002 11:56=20 AM

=20 =

sparafina
semiotech

Registered: May=20 2002
Location: AUS/LAX/DCA
Posts: = 223

quote:
Originally posted by lincomatic
thanks = for the=20 link. man, inside dimensional tolerance 0.5%. that's = going=20 to be tough with foam since it's so floppy. i wonder = how=20 critical the outside dimension is, or if it even = matters. i=20 like your fiberglass ideas...thinking of some groovy = paint=20 jobs like on surfboards...antennas don't have to be = ugly=20 anymore

Presenting the 20 dbi Mulletboy = slotted=20 waveguide!

sparafina has attached this image:
3D""=20

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07-24-2002 12:22=20 PM

=20 =

bmoore314
Mini=20 Stumbler
3D""=20