Tell me if this is feasible for an "Omni-Yagi": arrange multiple yagis
extending out from a central point in several different directions.
The different horizontal spines though would be pretty crowded within the
interior. I imagine there must be a reason why with a Yagi the various
spines are at a set distance from each other, otherwise you could more
reception by just placing them very close together.
Bob Clark
On Sat, Dec 16, 2017 at 2:40 PM, Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Sat, 16 Dec 2017, Marcus D. Leech wrote:
Moving up in frequency means the path-loss gets worse...
This is something that often confuses people; it's not that higher
frequencies actually incur more losses en route. The real issue is that
the way path loss is defined, it includes a separate question: what's the
aperture (effective collecting-area diameter) of an omni receive antenna?
The answer is that a radio photon has to pass within a fraction of a
wavelength of the antenna to interact with it... so an omni antenna's
aperture shrinks as the frequency rises.
Overall, omni-to-omni communications work better at lower frequencies.
Omni-to-dish (or vice versa; substitute other high-gain antennas for the
dish if desired) is pretty much frequency-agnostic. Dish-to-dish works
better as the frequency rises. (For all three, this assumes other things
are equal... which they often aren't.)
In VHF, it's perfectly reasonable to do omni-to-omni comms from orbit (or
to orbit), if data rates are modest or transmitter power is generous. Which
is just as well, because VHF high-gain antennas are big clumsy things.
(Our NORSAT-2 has a deployable VHF Yagi, but it's rather above the cubesat
class.)
In S-band or higher, well, not so much, unless you've got a *seriously*
muscular transmitter.
Henry
