None, the recommended length for mpx signals with rg58 is 1.80 m , for rg59 less than 3m , beyond these lengths you will have a strong loss of separation.
Orban 8100 manual
Composite ( Baseband) Output
Source Impedance: 470 ohms, independent of OUTPUT ATTEN setting, unbalanced.
Level: variable 0 to greater than 4V p- p by means of 15- turn OUTPUT ATTEN
Connector: Type BNC held floating over chassis ground to permit interface to
various exciters without need for wideband transformer for ground loop suppression.
Recommended Maximum Cable Length: 6ft ( 1.8m) RG-58A/U.
https://worldradiohistory.com/Archive-C ... l-1986.pdf