[Namaste-dev] Re: link budget

Matt Ettus matt at ettus.com
Wed May 28 22:06:02 PDT 2008


Howie AB2S wrote:
> OK, I know I am coming to the table a little late and I may have 
> missed something, BUT... from what I have been able to gleen from the 
> information posted so far; the satellite transponder will be a bent 
> pie (no onboard regeneration), with a global beam (about 18 dBi 
> antenna) and a 20W SSPA (EIRP about 31 dBW). The small ground station 
> will use a .5M antenna and 10W SSPA (EIRP 37 dBW). Using this 
> information and assuming typical Intelsat performance parameters of 
> SFD (Saturation Flux Density) of about -78 dB/m2, G/T of 0 dB/K and 
> modest Input and output back-off on satellite transponder, this link 
> will not work if these two stations are trying to communicate in 
> anything other than possibly CW. Given all of the above assumptions, 
> the nearest thing to a practical point to point link that I can come 
> up with is 16 kbps using 10 Watts and 2.4M (6') antennas at each end, 
> this was assuing a threshold Eb/N0 of 4.3db and BPSK modulation. So 
> what am I missing here? ........Howie AB2S


The ACP will definitely not be a bent pipe.  It will be demodulation, 
multiplexing, and remodulating the packets which are sent up to it.  It 
will act more like an ethernet switch than a repeater or transponder.  I 
don't know if you have access to the new OpenKM server that Dave put up, 
but if you do, you can read my docs.  I have several presentations up 
there, plus some air interface proposal documents.  In case you don't 
have access, I have attached a presentation I have given a number of 
times about the ACP.  It is longer (but slightly older) than the one I 
gave at Dayton.

We are also hoping to have more like 50W of power out of the ACP.

Matt

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