Created on 2008-12-08 18:14:00

Question

We need to test the analog audio performance of a Display Port interface. The device has multiple channels with RCA jacks. What type of cables do you recommend to form a matched cable set?

Resolution

Since the device has RCA jacks, for convenience, you might be tempted to use basic consumer audio (RCA) cables with RCA to BNC adapters. While this is adequate for many situations, for a critical application, and to ensure that you have a matched set, we would not recommend it. Consumer audio cables are less likely to adhere to the same rigorous standards as instrumentation cables. As a result, variations such as the gauge of conductors, the type of shielding used and how the cable is manufactured can cause differences in cable resistance and capacitance that can result in measurement anomalies.

For an application like this with unbalanced connections, we recommend using a good quality set of coaxial cables with BNC connectors.  For short lengths, such as the 14 inch cables contained in cable kit CAB-BNC, 50Ω (RG-58/U) cables are fine.  These 14 inch cables are intended for ” loopback ” testing (connecting the analyzer’s generator outputs directly to its inputs, for performance checks, etc.), and they are usually too short for general purpose use. For more typical lengths (36 inch or 1 meter), we recommend 75Ω (RG-59/U) cables from a reputable manufacturer like Pomona Electronics. These cables will provide years of trouble free service. For connecting the BNC cables to the RCA outputs on the device, use good quality BNC female to RCA plug adapters.