[amsat-bb] APRS to Moon orbit?

[Robert Bruninga]

Antenna area goes up as λ^2 but path loss also goes up by λ^2 so for the
same area the overall path loss is the same independent of frequency.  BUT
only with crossed dipoles can you get an omni pattern easily with two simple
wires.  Bob, WB4APR

-----Original Message-----
From: Eric Fort <eric.fort.listmail at fortconsulting.org>
Sent: Thursday, October 25, 2018 7:12 PM
To: Robert Bruninga <bruninga at usna.edu>
Cc: amsat-bb at amsat.org
Subject: Re: [amsat-bb] APRS to Moon orbit?

Speaking to aperture of the vhf antenna on the spacecraft.... isn’t aperture
related directly to wavelength?  Ie one wants to maximize λ^2 to maximize
gain.  That being the case, wouldn’t vhf give a smaller aperture for a given
allowable antenna size?.... or am I missing something about spacecraft or
other design criteria that limits these choices, or maybe I just plain have
this completely wrong!  If I missed something or got the relationship
between aperture and wavelength wrong, please educate me.

Af6ep

Sent using SMTP.

> On Oct 25, 2018, at 2:46 PM, Robert Bruninga <bruninga at usna.edu> wrote:
>
> Here's a crazy idea for APRS to moon orbit (omni antenna).
>
> Unless I did something wrong, I think an Oscar class long yagi, and
> 250W amp and 1200 baud FM packet can be received out near the moon
> with 3 dB margin?  A key factor is that the nearly 16 dB of assumed
> noise floor we have here on the ground at VHF does not exist in deep
> space.  And VHF gives the largest receive aperture for a crossed dipole on
> the spacecraft.
>
> The omni UHF downlink is a bear.  But with quad UHF long yagis and a
> 100W transmitter at the moon distance we still come up about 12 dB
> short.  Can we make up for that with distributed processing gain from
> a minimum of 16 Oscar class ground stations all phased together with
> the internet and GPS precise timing and a little software?
>
> If we could, then we have APRS out to moon orbit, with the downlink
> visible to all via the APRS internet system.  And in digipeating mode,
> we have half-earth coverage half the time when the moon is up.
>
> What did I do wrong?
>
> Bob, Wb4APR
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