Originally Posted by
dbsonic
> It locks down 2 x 2.4 frequencies per receiver at any point in time and shifting between them when needed, correct?
It's been a while since I worked on these for cell base stations, but it is probably a rake receiver. The idea is you take multiple antenna data and run it through a processing unit called an fpu (involving complex number signed math) and then combine the individual signal energies into a resultant signal with high signal to noise ratio.
Anyways, on the practical side, an old but interesting video from Spektrum on noise immunity:
https://www.youtube.com/watch?v=QaoXipp_288
Futaba FASST and FASSTest system use a combination of frequency hopping and direct sequence spread spectrum - as most systems do these days. On the other hand, the Spektrum receivers use a chip set that has significantly lower receiver sensitivity than others - which is one of the reasons that they require multiple satellite receivers to maintain a link.
That video is old and is a justification for Spektrum going from 2 static frequencies (DSM2) to frequency hopping (DSMX) - which again other systems did from the start.
Bob