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However, I wonder if the spektrum (after getting two clear channels) would fail if both channels were swamped? Probably (right?) then in a high traffic area wouldn't that be fairly likely? If so, why have we not seen a lot of crashes reported from both channels being swamped or have we? |
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It would, but it depends entirely on what's doing the swamping. Spektrum will
generally pick a couple of channels that aren't close to each other. If something
like a high powered 2.4Ghz video transmitter comes along, it may spread its signal
over 3-4 channels (actually probably closer to 8-10 of Spektrum's narrower channels),
but as long as it doesn't step on both of the channels Spektrum has selected, it'll be
fine. And even if it does, one of them is liable to be on the edge of the noise, and still
function. The type of noise that wipes out the whole 2.4Ghz spectrum and steps
on both of Spektrum's chosen frequencies at once, is going to hurt everyone else
as well. If there is any clear area, FASST will find it, but because it hops all
the time, it'll hop back into the noise as well. So if 90% of the spectrum is swamped
then FASST will lose 90% of its packets.
And keep in mind *none* of the 2.4Ghz *SS systems use 100% of the time on
channel. Typically it's closer to 10% utilization, and 90% of the time that frequency
is clear. That's why at even an extremely busy field, XPS, Spektrum, FASST,
Assan etc, all work happily. Even if they're on the same channel they're only
using it 10% of the time. If they lose a packet, they have different ways of dealing
with it. Some just ignore the lost packet and continue on (like FASST), and some
like XPS, lose the pack or the ACK from the Rx and send it again up to 3 times
before the next PPM frame. For Spektrum or XPS to be hurt by each other at all,
there'd need to be probably 5-6+ systems transmitting all on the same frequency
(XPS says up to 10 per channel, and from networking experience, we usually see
the collision rate starts to increase real fast at about 50% utilization of the wire).
ian