This video reviews a collection of coaxial cables, categorizing them into flexible, semi-rigid (soldered braid), and rigid ("hard line") types, noting their characteristics, quality, and potential applications. The rigid coax is highlighted as the "holy grail" for RF shielding due to its seamless copper pipe construction, though it is suitable only for permanent installations. Other high-quality semi-rigid cables from brands like Pasternac and United Microwave Products (UMP Microflex), often featuring foil wraps for enhanced shielding and high-frequency connectors (up to 26 GHz), are also examined. Using Time Domain Reflectometry (TDR) testing, the high-end cables demonstrate perfect 50-ohm impedance and negligible connector reflections. A key finding from the testing is that a simple right-angle SMA connector introduces a measurable impedance discontinuity (a blip to 60 ohms), demonstrating the impact of physical geometry on RF performance, even in high-quality assemblies.
Coaxial Cable Teardown and TDR Testing
0:08 Coax Cable Inventory: The video examines a collection of coaxial cables, sorting them into flexible, semi-rigid, and rigid categories to determine which ones are "keepers."
0:17 Flexible Cables (RG-174/RG-180): Standard flexible cables are shown, often used as pigtails. The RG-180 cable from Pasternac is noted as high-quality, though the common flexible cables are considered "dime a dozen."
1:14 Rigid Coax β The "Holy Grail": The rigid coaxial cable is described as a seamless, soldered copper pipe, similar to plumbing. This construction provides 100% RF shielding with no air gaps, making it ideal for "set and forget" permanent RF installations.
3:01 Semi-Rigid Coax (Tin-Lead Soldered Braid): This common type of semi-rigid cable features a fine copper braid covered in tin-lead solder. The connectors often incorporate both brass (for easy soldering) and stainless steel (for wear resistance and higher torque specs).
4:49 High-Frequency Flexible Coax (Foil Wrap): A second group of cables, including models like Pasternac SLL150 and UMP Microflex 165, are more flexible than traditional semi-rigid types. These cables utilize a foil wrap over a braid for superior shielding and feature high-frequency 2.9mm connectors, suitable for applications up to 26 GHz.
8:48 Time Domain Reflectometry (TDR) Testing: A fancy cable tester (TDR) is used to verify the impedance and quality of the connections.
8:56 Excellent Impedance Match: The rigid coax (hard line) tests perfectly at 50 ohms with almost no reflection or bounce at the connector site, confirming its high quality. The Pasternac and United Microwave semi-rigid/flexible cables also show perfect 50-ohm performance.
10:35 Right-Angle Connector Artifact: TDR testing reveals that a right-angle SMA connector introduces a small, measurable blip in impedance, momentarily rising from 50 ohms to 60 ohms, demonstrating how minor geometric features affect RF signals.
12:23 Cheap Cable Comparison: A generic flexible cable performs poorly in the TDR test compared to the high-quality items, showing much worse reflections and impedance mismatches.
Takeaway (8:23): All high-quality cables (rigid, semi-rigid, and high-frequency foil-wrapped ones) are considered "keepers" due to their superior shielding and confirmed 50-ohm integrity.