[amsat-bb] Re: Phase 4 versus Eagle
vk3jed at gmail.com
Sat Dec 15 13:45:48 PST 2007
At 04:13 AM 12/16/2007, Edward Cole wrote:
>I probably was not clear on this. That is also my assumption for
>mode-UV since there are unknown factors like sat power and antenna
>gain at this point. Since there does exist (hopefully not all have
>dissembled their stations) a lot of mode-UV stations from the
>AO-13/AO-40 era designing to that capability would make sense to me.
I'd agree there. While I don't currently have the capability of U
uplink, I could easily add the appropriate transceiver to my
collection. I already have V band capabilities. The final
ingredient would be to build some suitable antennas.
>For the HT orientation, the mw digital mode-SC (CC-rider update) is
>probably the correct approach. If this disappoints the HT - Leo
>crowd, I would point out that there ARE some physical realities to
>consider that may not make P4 as accommodating as a Leo (400km vs
Agreed. One practical path to HT access I see would take a leaf out
of the VoIP book, a ground station to access the bird and a network
of local repeaters for user access. That scenario's probably most
useful for emergency use, where a portable repeater with satellite
access can be brought in to an affected area to provide long haul
comms to the rest of the world, in parallel with HF
circuits. Similar ideas could be used to link the area for data
transmission as well. As for direct HT access, well as you say, we
are up against the laws of physics here, 38000km is a LONG way, even
with a line of sight path.
>But my intuition tells me that mode-LS is probably a better main comm
>frequency for satellite users. That will require gain antennas
>(20-dB) and moderate power (5-10w).
L is a good choice for the uplink, not as sure about S band these
days. You would require antennas with a clean radiation pattern and
reasonable satellite elevation, with all of the 2.4 GHz devices
around. X band is another downlink option that is of
interest. Antenna size would be nice as well, and since the target
is fixed, the antenna can be securely fixed to point at the nearest
bird in the constellation. When it comes to dishes, for me, smaller
is more practical, which suggests higher frequencies (C, X, etc).
73 de VK3JED
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