The difference between the Spektrum and Futaba RX antennas is simply their length. If you measure out the Futaba wires and the Spektrum wires on both the rx and sat, they should be pretty equal in length.Β*Β* What Spektrum does is adds an additional amplifier and puts the antenna plane at bothΒ* horizontal and vertical so it has a better field of view of the signal so no matter what attitude the plane is to the TX, it should always see the signal.
Futaba just uses two equal length wires and they are set at 90* to each other.Β* My guess is Futaba has an amplifier that works quite different than Spektrum ones, because even their non sat RX has two different length wires in it. Since they are not compatible with each other, the way they process signals is very different too, which goes back to the antenna orientations.
The only thing between all 2.4 radios that remains the same is, they transmit on 2.4 Ghz and use multiple channels. FHSS hops between channels, SS locks onto two channels, but I dont yet know how FASST works.
Some good tips on mounting the RX.
Edit: One thing I forgot, been quite a few years since I took the wireless classes, but this just popped into my head regarding the antennas, and it dawned on me about the Spektrum RX. In fact the Spektrum RX is in a sense a better RX for 2.4 Ghz. Reason being is antenna diversity. Have you ever noticed the wireless access points have 2 antennas, and now the N band have 3? Its because of signal diversity. The signal at 2.4 works totally different than 72Mhz. It is susceptible to Multipath distortion, and since the wave length is so small, it can arrive at the RX at two different rates, so the RX has to process those signals based on the strongest one seen. The more antenna, the better chance of picking up a strong signal no matter what attitude the plane is at.Β* Since Spektrum transmits wide band the signal is spread out wider, so diversity is important.
The Futaba RX doesnt use multiple antennas mainly because of how it transmits its signals. Since it does frequency hopping it sends the signal out at a tighter band, but jumps around the band and can deal with weak signals better.