Here is a very good link (pdf) that gives some great information:
http://www.aerocomm.com/docs/Antenna_Tutorial.pdf
Kurt
Quoting Doug McLaren <[EMAIL PROTECTED]>:
On Mon, Mar 24, 2008 at 11:47:16AM -0500, aeajr wrote:
| I believe the signal pattern on a 2.4 GHz system is the same as a 72 MHz
| system. Max signal is from the sides of the antenna. There is much
| less signal coming from the tip.
If two antennas have the same shape, and the wavelength to size ratios
are the same, then two antennas will have the same radiation pattern
even if on different bands. (i.e. double the wavelength, double the
size of the antenna, same radiation pattern.)
And in general, the 2.4 GHz TX antennas have the same shape (your
basic monopole/unipole/quarter-wave antenna) as your basic 7.2 MHz
antennas, so the radiation pattern should be the same.
However, there is room for differences, as the rest of the radio
affects the radiation pattern as well (even if it's not intentionally
part of the antenna, it's still part of the antenna), and so does that
guy holding it, and the ground certainly has an effect, and since the
ratio of the wavelength to the sizes and locations of these things
does vary, so will the radiation pattern.
To be sure, you'd have to either take a specific TX and situation and
model it, or actually measure it, but I imagine that what aeajr said
is probably close enough.
I'm still surprised that vendors aren't at least experimenting with
using a dipole antenna like this --
---| |---
======
| TX |
======
because that would create a radiation pattern where the strongest part
would be aimed right at your plane. And while it would also be aimed
right at you, a small shield could prevent that and increase the
useful signal aimed at your plane as well. And the gain is pretty
mild -- you'd still have good range even if not pointed right at your
plane.
| Pointing your antenna at the plane is not recommended.
It's not so bad. If you keep your antenna aimed at your plane, then
that will have approximately the lowest signal aimed right at your
plane, which will give you the earliest indication of any problems.
If you have problems, do like you do at 72 MHz and turn the antenna at
right angles to the plane and run towards it if that doesn't get
control back. This is if you're far out -- if you're close, then you
should not have problems, no matter what direction your antenna is
pointed.
--
Doug McLaren, [EMAIL PROTECTED]
If your parents never had children, chances are you won't, either.
--Dick Cavett
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