Supermac and Hypermac cable recommendations
- The minimum cable standard is Cat5e shielded STP (Screened Twisted Pair).
- Maximum length recommendation for multi stranded (flexible) cables : 75 Meters
- Maximum length recommendation for Single solid core cables: 100 Meters
- Any cable used for SuperMAC/HyperMAC must comply to the Cat5e standard for correct operation
Length
100m is the maximum length a Cat5e cable should be. But this does not mean all Cat5ea cable will be capable of running at 100m.
To determine the maximum length a SuperMac/HyperMac cable can be, a key parameter to consider is insertion loss. This insertion loss should be no greater than 24dB @100MHz for the chosen length of cable.
The physical construction of the high-speed signal conductors influences the Insertion Loss of the cable. When each signal conductor is made up from several thin strands of copper the Insertion Loss is greater (worse) than if the same cross-sectional area of conductor was made up from one solid core of copper wire.
This is unfortunate as the multi-stranded conductor is more flexible and easier to regularly coil on and off a cable drum, it will also lay flatter on the ground than a solid core cable.
The datasheet of a Cat5e cable should show insertion loss per 100m @ 100MHz. From this we can determine the maximum theoretical length.
𝑀𝑎𝑥𝐿𝑒𝑛𝑔𝑡h = 100 x SpecLimit/𝐷𝑎𝑡𝑎𝑠h𝑒𝑒𝑡𝑉𝑎𝑙𝑢𝑒
For example, Belden 74003PUd, Insertion Loss is 32dB/100m @100MHz
𝑀𝑎𝑥𝐿𝑒𝑛𝑔𝑡h = 100 x 24/32 = 75𝑚
Total length
When considering the cable length any patch bays and patch cables must be considered in the total length. It is also expected that the couplers used in any patch bays are going to contribute to insertion and return losses – though these are unlikely to carry any specification to help with your calculation. For this reason, patch bays should be avoided.
Screening
Cat5e cable can be unscreened or screened. Both are made from 8 insulated conductors twisted into 4 pairs. Unscreened (UTPe) the 4 pairs are wrapped in an insulating outer jacket. In the second type, screened, the pairs are wrapped in conductive foil (FTPf) or wire braid (STPg) before the insulating outer jacket
Connectors
Terminating the RJ45 to the cable needs to be done with great care, following the assembly instructions provided by good connector manufacturers. Errors in fitting the RJ45 connector may give errors in return loss. An RJ45 may look neatly connected to the cable but can still cause problems with return loss performance.
Cable Testing
While insertion loss is key to determining the maximum cable length, there are other parameters that need to be met for a cable to be a valid Cat5e cable. The only way to be sure of a good cable is to measure its Cat5e performance with a dedicated network cable analyzer. These do much more than measure continuity, shorts & resistance; they test normally hard to measure Cat5e parameters while sweeping the frequency where needed. Examples are the Fluke DTX-1800 and the DSX- 602
a Even cable categorized and marketed as Cat5e
b Insertion loss has a frequency dependent limit line specified from 1-100MHz, but often only 100MHz is specified in a datasheet.
c Other factors of the Cat5e standard limit this to 100m maximum
d Multi-stranded conductors – screened
e Unscreened Twisted Pair
f Foil screened Twisted Pair
g Screened Twisted Pair – often foil and braid