[Space] Debriefing Notes

Greg Stramback grog at piratelabs.com
Thu Feb 11 18:24:18 PST 2010


kicking myself for not replying to all at first...

as long as surrounding objects aren't metal (meaning nothing blocking the
radiating element's path) then things would be fine.



          |
          |   <---radiating element
          |
______|_______   <--- ground plane

so, obviously, everything that is either behind the ground-plane element is
fine to be metal or whatever else.

but a coax dipole really isn't a big deal... you just have to find some sort
of weight to hang it from the payload with to keep it vertical.  that and
they're easy to make, tune, and super cheap to replace.

you could also use coat-hanger or rods that can be soldered / attached to an
SO-239 (female large UHF style connector), mount _that_ to the bottom of the
payload...

there's a lot of options.  i need to actually get off my ass and get up to
NB to take a good look at this thing if i'm to give any solid suggestions.
 really kicking myself for being AWOL on sunday.  :-/

and to answer your original question, you can attach the antenna in any
non-metallic fashion you can think of so long as the radials aren't bent and
remain perpendicular to one another.  change those angles and you're
changing radiation pattern, tuning, you name it...

-g-

On Thu, Feb 11, 2010 at 5:58 PM, Mikolaj Habryn <dichro at rcpt.to> wrote:

> 19" radius makes for a fairly large slab, and just using stiff wires
> in the shape of a cross would make for some dangerously pointy bits
> falling out of the sky. The dipole sounds simpler and safer, although
> I'm also of the opinion that it would be worth using a stiff antenna
> attached to the side of the payload, since that way it would stay
> dipole shaped after landing, which might be useful for finding it if
> we land outside cellphone coverage.
>
> I'm imagining that our foamshell payload will wind up torpedo-shaped,
> meaning we could attach the antenna to the side. If it's offset
> somewhat from the body, it would presumably also reduce the arc
> through which the rest of the body would attenuate the signal. Can we
> attach an antenna at multiple points along its length with the
> appropriate materials? Or does it really want to only be attached at
> the base and to have clear air around it?
>
> m.
>
> On Thu, Feb 11, 2010 at 4:42 AM,  <grog at piratelabs.com> wrote:
> > Ed's right... but even in this previous situation, a dipole would
> probably have been a major improvement over the configuration that was used.
> >
> > On the other hand, a vertical dipole made out of coax would be cheap and
> less prone to damage from a landing.  it could hang from the payload section
> and stay (mostly - wind dependent) vertical with a fishing-line weight
> attached to it.
> >
> > Gregory Stramback
> > grog at pirate.org
> >
> >
> >
> >
> > On Feb 11, 2010, at 1:10 AM, Ed Moore wrote:
> >
> >> Radiation pattern - with a vertical dipole, half of the energy gets
> radiated up into space. with a ground plane and downward facing
> quarter-wave, the energy gets radiated from the horizon down (apart from a
> null along the axis of the antenna in both cases).
> >>
> >>       - Ed
> >>
> >>
> >> On 11 Feb 2010, at 09:05, Christie Dudley wrote:
> >>
> >>> I was talking to a friend tonight about this problem.  He suggested
> instead of depending on a ground plane, that we should instead use a dipole.
>  What are your thoughts on that?
> >>>
> >>> Christie
> >>> _______
> >>> "The road of excess leads to the palace of wisdom." -- W. Blake.
> >>>
> >>> The outer bounds is only the beginning.
> http://www.flickr.com/photos/genriel/sets/72157623376093724/
> >>>
> >>>
> >>> On Wed, Feb 10, 2010 at 11:35 PM, <nils at shkoo.com> wrote:
> >>> Cool. Googling "ground plane antenna" shows some promising hits; they
> mostly look like they put 4 horizontal wires in a plus-shaped configuration.
>  (Greg, I think this is what you suggested a couple weeks ago).
> >>>
> >>> I found an antenna simulation program here that one can use to simulate
> the radiation pattern of a given antenna:
> >>>
> >>> http://home.ict.nl/~arivoors/
> >>>
> >>> It's not working very reliably under my wine installation; perhaps
> someone else can have better luck.
> >>>
> >>> -nils
> >>>
> >>>
> >>> On Wed, 10 Feb 2010, Greg Stramback wrote:
> >>>
> >>> Well, you're using VHF on the 2m ham band. The groundplane should be a
> >>> minimum of 19" radius from the center feed point / radial.
> >>>
> >>> On Wednesday, February 10, 2010, Jonathan Moore <moore at eds.org> wrote:
> >>> On Wed, Feb 10, 2010 at 8:30 PM, Christie Dudley <longobord at gmail.com>
> wrote:
> >>> How big of a ground plane do you need?  We had a bit of a metal plate,
> but
> >>> it was pretty small, relatively speaking.
> >>>
> >>> It depends on how the antaina was designed.um
> >>>
> >>> -Jonathan
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