Text 1989, 210 rader
Skriven 2007-12-01 11:27:47 av Roy Witt (1:397/22)
   Kommentar till text 1967 av mark lewis (1:3634/12.0)
Ärende: yagi cantenna building...
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25 Nov 07 15:21, mark lewis wrote to Roy Witt:


 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.

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

Been too busy to even open my Fidonet reader. :o)

 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.

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

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

I don't think so...the can (with the alum lining or cover) would act as a
Faraday Shield. The only RF in or out will be via the open end. The bottom
isn't part of the antenna (since it's insolated from the driven element by
plastic). Although it will act as a reflector in a general way, but it's
not part of the active antenna.

 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.

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

Forgot about the tubing being used. Yes, that would be akin to having all
elements attached to the same boom.

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

I saw that in the design on the website.

 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?

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

In building a Wave Guided Horn antenna for Northrup Corp, I learned a
lesson in that solid metal contacts make a difference in antenna
performance.

Both of the two I built were intended to talk to each other across the
Mohave desert at UHF frequencies. There was an air gap in the tuning
mechanism that prevented the antenna from being flat across a wide
spectrum of frequencies. It was broadbanded enough for the customer's
needs, but had a flat spot right in the middle of the frequency they
wanted to use. By using a bit of RF 'grease', I was able to get them to
perform all across the bands from 120Mhz to 24Ghz...

 ml> [trim]

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

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

I would have used BNC connectors. Much easier to aquire and will work just
as well at 24Ghz.

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

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

I use that Linksys, dual antenna unit too.

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

For every 3db stated gain, you get a signal gain of twice the output per
each set of three. 10nw x 3 to fifth power = 160nw erp, while 10nw x 3 to
the sixth power = 240nw erp. (check my math, as I get confused when I
count on fingers) :o)

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

It's supposedly just as fast as the main computer connection, but I notice
a bit of a lag in my laptop, which is only connected to the internet via
wifi...

 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
 ml>> 10 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.

 ml> what we've got now, as described above, is an EZ-12 reflector and a
 ml> 7dbm gain omin on the outside of the RV with a 1.5 meter cable going
 ml> to the wifi card in the machine... google "ez-12" for more details...

 ml> oh, and this one i made from a "flattened" field peas can... yeah,
 ml> the normal, tall as your hand is wide, vegetable can... just
 ml> flattened and curved to fit the EZ-12 plans ;)  works a lot better
 ml> than the EZ-10s i made and tried out and no warranty voiding! :lol:

It's implemented like a corner reflector antenna...should have lots of
gain. If you play with the spacing of the reflector, you can vary the
signal strength at the trailer.

 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)

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

Yeah, there's way too much RF energy coming out of that wifi for that. :o)

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

You're welcome...keep us posted on your progress.

                R\%/itt


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