Can I use an IEEE-1394 (Firewire) cable longer than the 4.5m cable originally supplied with the E8491B?
The Agilent E8491B comes with a single 4.5m IEEE-1394 (Firewire) cable to connect two devices. Should additional length be required, 15 additional cables may be added to the system (for a total of 16 individual - 4.5m cables) to provide a total system cable length of 72m. This maximum length of 72m is an IEEE-1394 specification, as is the 4.5m length of a single cable.
Multiple 4.5m cables can be connected with the use of a repeater unit.
Commercially available IEEE-1394 Cable Boosters contain an interface chip which acts as a single repeater/amplifier and serves the purpose of connecting the individual 4.5m cables while maintaining signal quality and strength. Thus, each cable booster allows multiple hops or cable links (2 hops per cable booster). Since the cable booster draws power from the IEEE-1394 bus, it too is limited to the same specifications (max. 72m total cable length or 16 hops). The cable booster does provide the luxury of allowing different system configurations (i.e. tree and daisy-chain configurations) without additional E8491B's.
Agilent has not formally tested any repeater unit; informal tests of 3A International IEEE-1394 Cable Booster, 1394CB-400 have shown RFI problems with an early version of the product, but it otherwise seemed to work.