Text 1961, 94 rader
Skriven 2007-11-23 15:20:11 av Roy Witt (1:397/22)
   Kommentar till text 1940 av mark lewis (1:3634/12.0)
Ärende: yagi cantenna building...
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16 Nov 07 17:06, mark lewis wrote to all:


 ml> this isn't actually HAM related but it is redio related... hopefully
 ml> it won't be (too far) off-topic...

I think the rules will allow that.

 ml> i'm trying to finish up a yagi cantenna for my wifi router that i
 ml> just got... this is for 2.4Ghz... i've followed instruction on the
 ml> internet at o'riley's web site for a compact cantenna (the yagi
 ml> reflector is inside the can instead of outside) and i've a couple of
 ml> quick questions... yeah, i've one or two clues about antennas but
 ml> this is the first of this type i've played with...

You obviously know where to ask these questions, as you're in the right
ballpark.

 ml> my main question is about the reflectors... the instructions say
 ml> 1inch diameter washer with 1.2inch "spacers" (i'm using copper
 ml> tubing)... however, i've only got 1.5inch washers handy and i need,
 ml> by the plans, 5 of them... this is a 1/4 wave antenna...

    |  |  |  |  |
   -|--|--|--|--|-fwd
    |  |  |  |  |
    rl de dr dr dr

 ml> the question is, will the 1.5inch washers work or must i get some
 ml> 1inch ones?

2808/Freq in Mhz = 1/4 wave (in inches) 2808/2400Mhz = 1.17"

No. Your 1.5" washers won't work.

1" will sort of work for the directors (dr) although they should actually
be 1.1", and you should make the driven element (de) 1.17" and the
reflector (rl) at least 5% bigger, i.e. 1.23"...the spacing is somewhat
arbitrarily experimental, but you can use the designers spacing for now.

 ml> the plans also called for 1/8th in all-thread but i happaned to have

1/8th all-thread would be a #5 as in 5-40tpi...don't know if you can find
that at just any hardware store. You might be able to find #4 as in
4-40tpi, which is almost that big, about .116" diameter instead of .125"
1/8th. Do they mention whether or not the 'boom' has to make contact with
the elements? The boom would be the all-thread.

And, how do they feed this antenna? Some small coax, with the center
conductor connected to the driven element and the shield to the can? Or do
they use a matching device?

 ml> a threaded rod that is/was 1/4inch at the threads... but i didn't
 ml> need those threads as they were too far from the head... to i
 ml> threaded the rest of the shaft and then cut it down to length... the
 ml> shaft, itself, it 3/16ths... will this make any real difference?

No. In fact, it might help when you're looking for washers to use. BTW,
you'd be looking for 'fender' washers, since they've got the small holes
needed and the larger diameter of the standard washer. Hmmm, I wonder if
they make them that small.

 ml> i'm not looking for anything hugely amazing or such... i just need to
 ml> get this signal some 30 meters or so across the yard and into a metal
 ml> tag-along RV trailer...

You can do that with an omni antenna. I have a wifi sitting on a shelf in
by the computer and I can read a strong signal from across the street ...
60ft+25ft of yard?

 ml> according to the o'riley article, though, this thing should be good
 ml> for something like 12db gain and with two of them (one on each end)
 ml> and line of sight, the math says that they should be good for over 10
 ml> miles (!)... glad i'm just trying to go 30 meters :lol:

I don't think I'd try that with two yagis, especially can-tennas. I'd use
one yagi with an omni on the other end.

 ml> i can post more details if needed but i just wanted to touch base
 ml> with those who would be more into making their own antennas and see
 ml> what they have to say ;)

I've been making my own UHF antennas for quite a few years...yagis, quagis
and ground planes...designing and building antennas is lots of fun, moreso
than talking around the world on the radio. Of course, you need a license
to test them down range. :o)

                R\%/itt


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