Author Options:

Quick cantenna question / idea Answered

I've built a few cantenna's in the last few days and I've finally got one I'm really happy with, now I was wondering as radiowaves can't "see" holes that are significantly smaller than there wavelength (or so i understand) is there anything to stop me drilling say a 1/4" hole in the back, and making a sort of string cross-hairs on the front and sighting through the cantenna?



9 years ago

I drilled a hole in the back (3mm I think) crosshairs aren't really needed because looking down the can its very obvious what its pointed at. It hasnt nuked the gain in any way I can tell (signal strength varies by 2-3db even when its on a tripod) It makes it piss easy to aim and re-aim, and it's let me make a sort of text map of the hotspots I can see out of my window., I'll probably create a photo panorama map thingy when its daylight again. TBH I think cable losses are my main problem atm (about 2 1/2' of 3mm mini coax) so I'll have to buy some RG58 or something and re terminate my connections. While I'm having a mumble, can anyone tell me how making the can longer effects performance, Do I get more gain / narrower beam like a yagi or is this whole thing meant to be a critical length?

. There is a diameter/length/frequency calculator on this Cantenna How-To page.
. IIRC (but not real sure), you can use a guide that is 2x, 4x, 1/2x, 1/4x, &c (even integer multiples) the optimum length. Experiment and let us know what happens.

'tis the same site I used. I managed to find some cans that are bang on 3.25' (which seems to be the optimum size) I had previously made ones that were 4.25 and 3.75 and both were just too big, not useless, but nothing to write home about. He seems to just say as long as possible which doesnt really help me. I'll solder another can on the end tomorrow and see if I can get an improvement, but as I said before the signal is up and down like a yoyo anyway, and my cable losses are high so any improvement will be more subjective than numerical.

. One doesn't aim a cantenna. Guess things change. ;)
. If what you are aiming at is more than about 100 feet (30 meters) away, then parallax shouldn't be a problem - just mount your aiming device to the side of the can.

Probably not - try it, test it, post an instructable!