-BackgroundThe Tempest wireless intercom system is a spread spectrum, frequency hopping system that transmits 10msworth of audio in a 5ms RF burst.  It then moves to a different transmission frequency.  The Tempest network number determines the hopping pattern and the sync makes the basestations (and their associated beltpacks) "hop" together betweenfrequencies.  - Tempest SyncWhenthere are two more base stations (or their antennas) are close together, the sync is criticalas the alternative is that two, or more systems, are bombarding each other with250mW of RF power using a 900MHz system. As you increase the distance between the systems thisbecomes this becomes less critical as the systems will start to see each otheras the RF noise floor. Yourmileage may vary on when you need to be concerned with the sync, depending on RFproportional characteristics of your environment, somewhat like when designingspeaker systems. Anotherpart of the equation is how many other Tempest systems may be around. It is a good idea to play with the system todevelop a "feel" for how distance between systems, and architecture,affects system performance, synced and un-synced. Theperformance difference is easily determined initially where that they areunusable when next to each other to becoming a subjective evaluation of theaudio quality of the two systems (evaluate one, then both together).It is generally recommended to sync basestations together if their antennas are with 400ft (130m) of each other ---Distribution of the Accusync (and Z-Sync)TheAccusync uses the first 5 pins of the DB9 connectors.  The cable should bepinned 1:1.  Long runs  are allowed (1000ft+). A CAT cable is suitable for distribution of the Tempest sync signals. It is quite common to see 9pinto RJ45 adapters on back of devices (molded plastic adapters).  This allows for Tempest sync distribution with readily available cables. Thereare no available Ethernet or fiber converters for the Accusync.  The syncis very time critical and the hypothetical conversion to those mediums does not allow for this. ---Differences between Tempest 900MHz and 2400MHzThe Tempest 900 has the upside of being able to better penetrate walls etc due tolower frequency.  The longer wavelengths make for a more solidperformance on the edges of the coverage area.Italso has the benefit of being in a spectrum that is often not as crowded as the2400MHz. Theshorter wavelengths of the 2400, and more spectrum, allow for a tighter andmore precise stacking of frequencies in the air.  2400allows us to sync up to 11 base adjacent base stations.  The 900 allowsfor 3-4 base stations. As Tempest 2400 came of age it got the additional capability of"Roaming" where beltpacks can be seamlessly handed over between basestations (like cellphones between cell towers) in order to add coverage to thesystem.  Todo this seamlessly in a digital system, without massive glitches, precision isrequired that is not possible to achieve in the 900MHz spectrum due to longwavelengths.  Hence,roaming is only available in the 2400 system and the 900 system requires theuser to manually select another base station from the beltpack.  Tobe able to roam in a 2400 system the following must be in place:1)The beltpacks, base stations and remote transceivers must be running Radioversion 1.18 or higher (all since since mid-2012).  Earlier devices can besent into the factory for an upgrade.2) AZ-Sync generator must be used to synchronize the system.  This is an externalclock generator that is available either in the form factor of a DB9 connector(SG100) with a PSU that connects to the first device and then daisy chainstrough the rest the system OR as a rackmount device that has 12 outputs.
Z-Syncis only available for 2400 systems. ---The difference between Z-Sync and Accusync:ImagineAccusync is WordClock that holds a certain beat. Z-Sync is TimeCode where everybeat also has information on what time it is. This allows all synchronized devices tojump together with even more precision. 
Note Tempest 900 systems are only for sale in N.America