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December 11th 03, 12:13 AM

(Simon) wrote in message . com...
Hi,
I'm playing around with some 433MHz transmitter and receiver pairs.
Ideally I would like the transmitter to transmit in a narrow
directional beam, but I'm new to the art of radio waves and antenna
design, so I was wondering if you guys would be able to help me with
my project. I've read about a Yagi design for the antenna, I know it
receives from one direction only, but does it transmit in just one
direction too?

Yes, antennas have the same directionality transmitting and receiving.

I thought I'd be able to basically stick the transmitter antenna in a
tube, sealed at one end, line either the inside or outside of the tube
with tin foil (or both) and it would transmit in whatever direction
the open end was facing. So far my tests haven't been too conclusive
but could that be poor setup on my part or

----is the idea fundamentally flawed?----

Yes. You could do it, but you'd probably want a horn-shaped tube, and
the diameter at the outer end would have to be large compared with the
wavelength to do much good. You'll probably find the Yagi a lot
easier to do, using common materials like some 3/4" PVC pipe with
holes drilled through it, and ordinary 12-gauge or 10-gauge solid
copper wire put through the holes. You can use bare wire or wire with
insulation. The elements (wires) are only about 13-14 inches long, so
wire like that will be stiff enough to hold its shape well when
supported in the middle by the PVC (or a wood dowel, or...use your
imagination for other ideas). You should be able to find construction
ideas for Yagis on the web. You can scale the size with frequency
(size1*freq1=size2*freq2), but be sure to scale the element diameters
at least approximately, and not just the lengths and spacings. (Don't
use an 0.1" diameter wire if the plans call for 0.5" at that
frequency.)

Cheers,
Tom