[amsat-bb] Re: Phase 4 versus Eagle

[Tony Langdon]

At 04:13 AM 12/16/2007, Edward Cole wrote:
>Les,
>
>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
>37,600km range).

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
http://vkradio.com