There are arrays of multiple yagi or log periodic antennas used in
direction finding I have seen some with as many as 60 under a dome.
Problem is still there because the beam goes out horizontal and not
vertically. You can increase the vertical beamwith somewhat by reducing
the number of elements but at the same time you lose the gain you
needed.
You can hand track a ham sat with a yagi using a camera tripod if you
want but to do anything with a cubesat you need automated tracking and a
beam antenna with sufficient gain.
You need a helical a dish or a crossed yagi and a tracker to catch the
small power output of a cubesat.
I like antennas though some do have uses like slot antennas are useful
sometimes on spacecraft.
I am disappointed in the telemetry gathering done in amateur rocketry
but it is moving forward ever so slowly. I like the progress in the
drone market, almost all of their stuff can apply to rockets.
Monroe
-------- Original Message --------
Subject: [AR] Re: SDR Radio's was "infrastructure" (was Re: Amateur
solid rockets for ...)
From: Robert Clark <rgregoryclark@xxxxxxxxx>
Date: Sat, December 16, 2017 5:08 pm
To: arocket@xxxxxxxxxxxxx
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
