Text 1967, 145 rader
Skriven 2007-11-25 15:21:17 av mark lewis (1:3634/12.0)
   Kommentar till text 1961 av Roy Witt (1:397/22)
Ärende: yagi cantenna building...
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 ml> this isn't actually HAM related but it is redio related... hopefully
 ml> it won't be (too far) off-topic...

 RW> I think the rules will allow that.

thanks! i was wondering when you'd chime in ;)

 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...

 RW>     |  |  |  |  |
 RW>    -|--|--|--|--|-fwd
 RW>     |  |  |  |  |
 RW>     rl de dr dr dr

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

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

 RW> No. Your 1.5" washers won't work.

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

ahh... ok... their measures by the formula(s) were 1.20 for the longest and
1.22 for the shortest wave freq... so i can see where they were going with the
1 inch washers...

the reflector is the metal base of the pringles can ;)

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

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

well, they were putting aluminum tubing over the all-thread as spacers between
the washers and to hold the washers in place... i would expect that there is
electrical contact all the way thru... i used copper tubing and there is
electrical contact there ;)

also, the boom does not touch the reflector or the driven element... there is
an air gap between them...

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

coax to the can with the center becoming the driven element... the inside of
the pringles can is supposedly conductive... how that reacts with the metal
base as the reflector, i don't know... i just know a lot of folk have used them
and bean cans and coffee cans and even plastic water bottles with wire window
screen as the reflector and wave guide ;)

[trim]

 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...

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

we couldn't get much more than 18 to 24 signal strength until we mounted a 7db
gain antenna outside the RV... then it went quite a bit higher when i fashioned
a bean can into a reflector to sit behind the dlink's 6 inch omni... i haven't
gotten any rp-sma ends to put on my cantennas (yet)...

my mother was up for thanksgiving and brought her new laptop which she wanted
me to set up... since she also wanted wifi for it, we tested it here with what
i have in place... i have to remove the reflector but still had some "problems"
with loosing signal strength...

last night, we went in to town to get another dlink wbr-2310 like the one we
have... they weren't on sale like they had been a couple of weeks ago... since
we already had to stop over at radio shack, we looked at what they had... a
linksys WRT54G came out with us... i plugged it into the same switch as the
dlink and set it on the shelf right beside the dlink... with no reflectors on
it, the laptop was able to get connected and go surfing... that was some 45
feet thru the house with at least two walls between...

i went out to the RV and was _very_ surprised to see the linksys (with no
reflectors) was being received at 80 and the dlink with a reflector was being
received at 68... that let me to power and i was able to finally find out that
the dlink is rated at 15dbm +-2dbm whereas the linksys, with dual antennas
versus the single one on the dlink, is said to be 18dbm and no +- listed...

and to think, all this just because someone wanted to save $20US :?  the
frustration and bickering cost more than that! they were just ready to take the
whole mess and chick it because they couldn't get to the internet... kept
saying that it wasn't working when i was plainly getting into the computer room
and all the way to the modem... i finally powered the modem off for 10 minutes
or so and then got another IP address in another Class-A block and things have
been peachy ever since... i _think_ (but i could be wrong) that they finally
understand that not all problems are the wifi and that it could easily be the
internet connection with my provider... their main thing was they were seeing
the same result in their eyes... that result being that the couldn't get to
their homepage and with that in mind, the problem must be "this wifi shit that
just don't work"... arrrrgh!!

 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:

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

what we've got now, as described above, is an EZ-12 reflector and a 7dbm gain
omin on the outside of the RV with a 1.5 meter cable going to the wifi card in
the machine... google "ez-12" for more details... oh, and this one i made from
a "flattened" field peas can... yeah, the normal, tall as your hand is wide,
vegetable can... just flattened and curved to fit the EZ-12 plans ;)  works a
lot better than the EZ-10s i made and tried out and no warranty voiding! :lol:

 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 ;)

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

yeah, that's what they say... i've got a 10 foot mesh satellite dish... wonder
if i'd get in any trouble if i fixed it up to blast this wifi at that RV? nah,
it might burn the RV to the ground, hahaha :? ;) ;)

thanks for the feedback... it has been a fun experience and got moreso once i
got "them" to realize "homebuild antenna shit" is how things used to be done
and this was good fun working on the design and building it/them ;)

)\/(ark

 * Origin:  (1:3634/12)