We have some Belden 6341PC cable which will be used with some RS-485 communications equipment, which of I'm learning will need line terminators. I'm told the resistor values needed should match the characteristic impedance of the cable. The problem is I'm not seeing anything on the datasheet which explicitly mentions the impedance.

I also see that, according to the spec sheet, this cable is rated as being for 'Pro Audio and Intercom Systems', not RS-485 systems.

1) Based on the info on the spec sheet, is there a way to determine which resister termination value should be used?

2) Should I recommend another cable be used instead? The problem is the cable has already been pulled, so we're hoping it'll work without issues.

  • 2
    \$\begingroup\$ IMO, step 1 is to try 120 Ohms. If it works, problem solved! \$\endgroup\$ Jan 8, 2018 at 19:02

1 Answer 1


Impedance on cables is defined by the ratio of distributed reactance of L/C as follows.

\$Z_o=\sqrt {\frac{L}{C}}\$ for L= 0.16 uH/ft for each line and C= 44 pF/ft, line to line thus;
\$Z_0= \sqrt{\frac{0.16uH}{44pF}}=60 Ω\$ for each line and thus differential Zo = 120 Ω


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.