Navigating the world of wireless microphones can quickly lead to technical questions, especially when it comes to optimizing your antenna setup. If you’re new to wireless systems, like the user who recently purchased Shure ULXP units and encountered a recommendation for 75 ohm coax cable for antennas, you might be scratching your head about impedance. Is 75 ohm cable really better, or is it “BS,” as the original poster wondered? Let’s clarify the differences between 50 ohm and 75 ohm coaxial cables and determine the best choice for your wireless microphone antennas.
To understand this, it’s important to grasp the basics of coaxial cable construction. A coax cable consists of a central conductor, an insulating dielectric material surrounding it, and an outer shield, typically made of copper or aluminum, all encased in an outer jacket. The key differentiator between coax cables lies in their impedance, a characteristic determined by the cable’s physical dimensions and the dielectric material.
Industry standards have largely settled on two primary impedance values for coaxial cables: 50 ohm and 75 ohm. But what do these numbers mean, and when should you use each type?
50 Ohm vs 75 Ohm Coaxial Cable: Understanding the Difference
The eBay seller quoted in the original post provided a useful summary:
“With 50 Ohm Coaxial Cables being the best compromise solution, practically any application that demands high power handling capacity, i.e. 100 watts or more, will use 50 Ohm Coaxial Cable. A good rule of thumb is that any device that functions as a transmitter or transceiver tends to use 50 Ohm Coaxial Cable. This includes devices such as CB/Ham Radios, Broadcast Radio/TV Transmitters, Wi-Fi and Cellular Phone Repeaters and 2-Way Radios (Walkie Talkies). However, not every case warrants high power handling, so 50 Ohm Coaxial Cable is not appropriate for every application. When the objective is to ensure that the signal gets through the cable in the most efficient way possible, losing very little signal strength in the process, 75 Ohm Coaxial Cable is the way to go. A good rule of thumb is that if the device being connected via coaxial cable is a receiver of some kind, 75 Ohm Coax is ideal. This includes devices such as Satellite and Cable TV Receiver Boxes, High Definition Televisions, AM/FM Radio Receivers and Police Scanners.”
Essentially, 50 ohm cable is optimized for power transmission, making it ideal for transmitters. Think of applications where signal strength and power delivery are paramount, such as radio transmitters and two-way communication systems. On the other hand, 75 ohm cable is designed for signal purity and low signal loss, crucial for receiver applications like television and data signals where maintaining signal integrity over distance is key.
Why Shure Recommends 50 Ohm Cable for Wireless Microphone Antennas
The crucial point for wireless microphone systems, and specifically for the Shure ULXP units mentioned, is that these systems are transceivers. A wireless microphone system includes both a transmitter (the microphone itself) and a receiver (the unit connected to your sound system). Furthermore, antenna distribution systems used to enhance wireless mic performance also handle both transmitting and receiving signals.
Shure, a reputable manufacturer in the audio industry, specifies 50 ohm cable and connectors for their wireless microphone systems. This recommendation is not arbitrary. Using the correct impedance is vital for efficient signal transfer and minimizing signal loss and reflections (VSWR – Voltage Standing Wave Ratio). Mismatched impedance can lead to signal degradation and reduced range, counteracting the benefits of using external antennas.
While 75 ohm cable might offer slightly lower signal loss per foot in certain receiving applications, the impedance mismatch in a 50 ohm system can introduce more significant losses and performance issues. For wireless microphone systems, maintaining impedance matching across the entire system – from the antenna to the receiver – is more critical than chasing marginally lower loss figures offered by 75 ohm cable in a mismatched setup.
In conclusion, for your Shure ULXP wireless microphone systems and similar setups, sticking with 50 ohm coaxial cable and connectors is the correct and manufacturer-recommended approach. The eBay seller’s blanket statement favoring 75 ohm cable doesn’t hold true for transceiver-based systems like wireless microphones. Always prioritize the manufacturer’s specifications to ensure optimal performance and reliability for your wireless audio.
