Ok I like it when Wikipedia can answer my questions:
See
Spread Spectrum
Direct-sequence spread spectrum link
In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated. The name 'spread spectrum' comes from the fact that the carrier signals occur over the full bandwidth (spectrum) of a device's transmitting frequency.
Features
1. It phase-modulates a sine wave pseudorandomly with a continuous string of pseudonoise (PN) code symbols called "chips", each of which has a much shorter duration than an information bit. That is, each information bit is modulated by a sequence of much faster chips. Therefore, the chip rate is much higher than the information signal bit rate.
2. It uses a signal structure in which the sequence of chips produced by the transmitter is known a priori by the receiver. The receiver can then use the same PN sequence to counteract the effect of the PN sequence on the received signal in order to reconstruct the information signal.
So each bit sent is modulated by several PN or chip codes that shift the carrier frequency. Then each of these chips is decoded by the Rx. Chips that don't decode correctly can be discarded. Several devices can co-exist on the same channel because they don't have the came PN sequence. Even if they do have a chip collide its no crutial as others with the same bit of information will get through unharmed.
Frequency-hopping spread spectrum link
is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver.
A spread-spectrum transmission offers three main advantages over a fixed-frequency transmission:
1. Spread-spectrum signals are highly resistant to narrowband interference. The process of re-collecting a spread signal spreads out the interfering signal, causing it to recede into the background.
2. Spread-spectrum signals are difficult to intercept. A frequency-hop spread-spectrum signal simply sounds like an increase in the background noise to a narrowband receiver.
3. Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference. The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result, bandwidth can be utilized more efficiently.
continues:
One of the challenges of frequency-hopping systems is to synchronize the transmitter and receiver. One approach is to have a guarantee that the transmitter will use all the channels in a fixed period of time. The receiver can then find the transmitter by picking a random channel and listening for valid data on that channel. The transmitter's data is identified by a special sequence of data that is unlikely to occur over the segment of data for this channel and the segment can have a checksum for integrity and further identification. The transmitter and receiver can use fixed tables of channel sequences so that once synchronized they can maintain communication by following the table. On each channel segment, the transmitter can send its current location in the table.
and:
In the US, FCC part 15 on unlicensed system in the 900MHz and 2.4GHz bands permits more power than non-spread spectrum systems. Both frequency hopping and direct sequence systems can transmit at 1 Watt. The limit is increased from 1 milliwatt to 1 watt or a thousand times increase. The FCC prescribes a minimum number of channels and a maximum dwell time for each channel.
This is the technique that Futaba is using. Its also the system that the US military uses for its field radios. This has distinct advantages when the signal band is saturated with lots of fixed frequency devices. Do note that each individual reception on a channel is still in the same way as Direct-sequence spread spectrum, with multiple chips per bit. So this is DSSS with Hopping added, not simply a narrow band carrier hopping around.
Sorry for the long post but I hope this is useful information. I am certainly more enlightened for having done a little reading.