[amsat-bb] APRS to Moon orbit?

[Eric Fort]

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 

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> 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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