[amsat-bb] Re: 'Zombie-sat' and the clever orbital dance

[Nigel Gunn G8IFF/W8IFF]

Where does one find this information?


On 27-May-10 11:44, Bill Jones wrote:

> I think the transponders on both sats are 36MHz wide, spaced every 40 MHz. AMC-11
> has vertical transponders at 3720, 3760,.....4120,4160  and horizontal from
> 3740,3780,...4140,4180.  There is about a 4 MHz gap between each transponder, but
> I am not sure just how sharp the dropoff of the bands are, and how effective this
> 4 MHz gap really is.  The Galaxy 15 transponders are at the same places, but the
> vertical are where the AMC11 horizontal are, and visa-versa.  For narrower
> signals which aren't centered at the transponder center, are within the bandwidth
> of both horizontal and vertical transponders. For example the QVC shopping
> channel is an approximately 15 MHz wide vertical signal centered at 3928. It's on
> the 3902-3938 "3920" transponder on AMC-11, but would also almost fit into the
> 3922-3958 "3940" transponder on Galaxy-15.
>     Most of AMC-11's transponders however are centered on the nulls between the
> Galaxy-15s transponders. I am not at all clear with respect to what this would do
> to the signal. Sort of seems like the 4 MHz gaps would be like a notch filter,
> and would be somewhat similar to removing the carrier when generating a SSB
> signal. These digital signals look very broad and rectangular in a spectrum
> analyzer.  Most are 20 or 30 MHz wide, and if you remove a 4 MHz wide segment
> from the middle, I assume that it would result in significant distortion,
> regardless of whether you leave the AMC-11 transponders on or off, but I really
> don't understand much at all about how removing part of the envelope of a broad
> digital signal like this affects the reception. Since these are mostly QPSK an
> 8PSK signals, it doesn't take much interference from similar symbol rate signals
> to mess up the reception of these things, particularly because the phases will be
> different from G-15.