Text 1955, 82 rader
Skriven 2007-11-19 11:10:36 av mark lewis (1:3634/12.0)
   Kommentar till text 1953 av Richard Webb (1:116/901.0)
Ärende: yagi cantenna building...
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ml> my biggest problem is figuring out what part the washers play in the
ml> whole thing... i know their spacing is 1.2 inches... should they
ml> also be 1.2 inches in diameter?

 RW> TOugh question, especially when we don't know if they're actually
 RW> supposed to be elements.  Plug the term yagi into your favorite
 RW> search engine you'll  find all sorts of dimensions for yagis and
 RW> the formulae to derive them for your frequencies of interest.  THat
 RW> might help you. Iirc and I am doing this pre coffee the reflectors
 RW> are usually behind the driven element, and often a bit longer.

actually, i've some to the conclusion that it is a yagi and the numbers to work
out by other formulas i've found on the 'net... i think the only difference is
that instead of the directors being a length of wire, they're supposed to be
washers of the needed diameter... just think of the diameter of the washer in
the same sense as you would the length of wire for the directors and it seems
to work...

i actually worked thru the numbers and a fullwave 2.4Ghz antenna tuned for the
center of the wifi band wouldn't be all that hard to construct... i mean,
heck... the wavelength is only 4.88" ;)

[trim]

ml> i went and looked at lowes today to see if i could find some 3/16ths
ml> x 1 inch and they didn't have any... they did have 1.25s and .75s
ml> but not the 1's in a 3/16ths hole... heck, i might just go ahead and
ml> break down and buy some 1/8th inch all-thread and the washers to fit
ml> that with some tubing, too... all total, it would be less than $10
ml> :)

 RW> Yah I think I would so that it'll work as advertised, especially if
 RW> it's to link something into your network.  REmember this thing has
 RW> to transmit too, and even though it's low power the transmitter
 RW> will be much happier seeing the proper 50 ohm impedance etc. AT
 RW> these frequencies you're dealing with low tolerances and any loss
 RW> is bad.  ESpecially from your home to the neighboring rv, both
 RW> metal skins iirc.

yeah but i'm pointing the router/WAP end out of a window... it is the other end
that's being a bit of a bugger... partly due to the angle of attack... by that
i mean that we're not at 90 degrees... the beams are having to travel
diagonally thru the outside wall on the other end... extremely rough
guesstimate would say maybe a 10 or 15 degree angle... yeah, it makes the wall
look thicker but it's the best we can do :?

ml> but then again, free is better :lol:  i wonder what king of blast
ml> i'd get by hooking up this old three legged scanner antenna that's
ml> up on the roof ;) 

 RW> I'd say not near as good.  THat old antenna went into uhf but not
 RW> into that range. I'd guess its top range would be around 512 mhz. 
 RW> Also your feed line loss is probably going to be pretty huge. I'm
 RW> mostly an old school high frequency guy so others who dabble in the
 RW> microwave stuff could advise you a bit better, but that's my take
 RW> on this  thing anyway. My vhf/uhf setup here at the house is less
 RW> than optimum in some respects.  I've got a hundred foot run of rg-8
 RW> feeding a j pole 60 foot up in a big old oak tree.  NOw the problem
 RW> is line loss, as there's a barrel connector connecting two runs of
 RW> coax to make it that far. WERe i Really going to do it right I"d
 RW> get some 7/8 inch hard line to run to that antenna. I still can hit
 RW> just about anything I want, from 30 miles east of MEmphis Tn. I can
 RW> hit the Jackson Tn. main repeater system reliably any time I need
 RW> to. THat's with 50 watts.

yeah, i know what you mean... i've been reading and learning... it is quite
interesting, in fact... i mentioned working the math with formulas that i found
somewhere else than the cantenna site(s)... those were from a canadian site
that has plans for a 3 element and 6 element yagi tuned for some FM radio
station frequency of your choice... you choose the station that's like 200km
away, build the antenna, mount it, set it with a 30 degree angle to the ground
pointing in the direction of the FM station and then listen for the station's
signal to bounce off of ionized meteor trails so you can count the meteors ;)
;)

i worked thru that stuff using the 2.4Ghz numbers and from what i can see,
everything it right even if i am working fullwave and they're working
quaterwave :)

)\/(ark

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