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Re: Datacomms on P3D


Martyn Kinder G0CZD wrote:

> I'm also a little confused about the datacomms bandplan for P3D which shows
> an Anologue type allocation that is not specifically channelised.

This is because we use the common IF approach on P3-D in connecting
any combination of RX's and TX's and also for bandplanning.

While some of the digital uplinks and downlinks are fixed frequencies,
the DSP based modems can be programmed for any frequency within this
segment (even outside if needed).

The transmitters are linear, so what you see is what you get at the
IF input. Since it was not practical to have analog and digital mixed,
and also to help the experiment designers, we made these reservations
for analog and digital.

> Can someone give me some hints as to the type of Datacomms that P3D will be
> used for. 

The RUDAK experiment will be fully compatible to the PACSAT protocol
suite, i.e. Store&Forward BBS to also download Images from the
camera and other data and indeed personal messages, bulletins.

Among the standard 9600 baud G3RUH FSK type of modulation, we also
have two uplinks/downlinks at 153 KBit/s PSK and a couple
of additional uplinks/downlinks using the DSP modems.
The later can be indeed programmed for any sort of modulation
which is efficient for satellite usage.

However, for Store&Forward gateway activity we would prefer usage
of the highspeed 153 KBit/s link, which could also be used for
global interlinks to packet networks between countries.

The Pacsat Broadcast protocol will be much more efficient than
on a LEO satellite because of the larger footprint and much
longer availability. Much more stations can benefit from downloading
the same file. With P3-D in the final orbit, the northern hemisphere 
will have almost 24 hours availability.. You don't have to wait
12 hours unless you use a fixed antenna!

2-way connects should also be possible, but perhaps protocols
like DAMA (demand assigned multiple access, which is very popular in Europe!)
need to be implemented to reduce collisions of users at the uplink.
I also think that a "converse mode" round table would be a great
thing, but this kind of software still needs to be implemented on RUDAK.

Basically, you can use your existing 9k6 PACSAT groundstation for P3-D.
But we might later want to use more power efficient modulation.

Hope this helps,
 73s Peter DB2OS

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