50 Ohm VS. 75 Ohm, Which One is the Best Coaxial Cable?
There are many copper-based applications existing in telecommunication networks, although the fiber has dominated the market. Twinax cable, twisted pair cable, and coaxial cable are three commonly used copper cables in our daily life, and we are familiar with twinax cable, like 10G DAC or 40G DAC, and twisted pair cable, like cat5e or cat6, since we have introduce them several times before in my previous blogs. How about coaxial cable? Coaxial cable as shown below is the kind of copper cable used as a transmission line for radio frequency signals. The term “coaxial” comes from the inner conductor and the outer shield sharing one geometric axis. Now, not all coaxial cable is created equal and that is where the coaxial cable impedance comes into play. Generally, there are two types of coaxial cables: one is with an impedance of 75 Ohm, used mostly for video applications, and the other is with an impedance of 50 Ohm, used mostly for data and wireless communications. Which one is the best? Read the following text, and you will get the right answer.
What Does Ohm Refer to?
An Ohm is a unit of resistance—that is the resistance to the flow of electrical current through a circuit. In the most basic applications, where we are dealing with DC or direct current electricity, such as that from a typical 12-volt car battery, we are measuring the resistance in Ohms. However, the second we try and send AC or alternating current through a circuit, we are no longer measuring resistance, we are measuring impedance. Typically, the smaller the Ohm, the better the performance. So a 50 Ohm cable provides much better results than a 75 Ohm one.
50 Ohm Coaxial Cable
The standardization of 50 Ohm impedance goes back to developing coaxial cables for Kilowatt radio transmitter in the 1930s. Actually, according to the experiment conducted by experts proving that the minimum insertion loss was achieved by a 77 Ohm, while the best power handling occurs at 30 Ohm. But there are few dielectric materials suitable for use in a coaxial cable to support 30 Ohm impedance. Thus, the choice of 50 Ohm is a compromise between power handling capability and single loss per unit length, for air dielectric.
With 50 Ohm coaxial cable being the best compromise solution, practically any application that demands high power handling capacity, like 100 watts or more, will use 50 Ohm coaxial cable. The primary use of a 50 Ohm coaxial cable is transmission of a data signal in a two-way communication system. Some common applications for 50 Ohm coaxial cable are computer Ethernet backbones, wireless antenna feed cables, GPS (global positioning satellite) antenna feed cables and cell phone systems.
70 Ohm Coaxial Cable
Although 50 Ohm is preferred in many applications, it is not appropriate for all applications, since not every case warrants high power handling. For example, 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, we need a 75 Ohm coaxial cable instead of a 50 Ohm.
Technically, 93 Ohm coaxial cable has the lowest capacities of any type, but 93 Ohm coax is rare and expensive. Thus, 75 Ohm coaxial cable is the closest fit, offering not only low signal attenuation loss, but also relatively low capacitance. The primary application of 75 Ohm cable is to transmit a video signal. One of the typical applications is television signals over cable, sometimes called signal feed cables. Another application of 75 Ohm coaxial cable is video signals between components, such as DVD players, VCRs or Receivers commonly known as audio/video (A/V) cables.
Choosing 50 Ohm or 75 Ohm?
50 Ohm and 75 Ohm values refer to the impedance of the coaxial cable. The main difference between these two coaxial cable types is their applications. The primary application is the transmission of a video signal, and in the case of 50 Ohm cable, it is a data signal that is for the most part being transmitted. Simply put, 75 Ohm cable is for picture, while the 50 Ohm cable is for information. For choosing the right coaxial cable, you should figure out what you application type. We can easily tell the appearance difference of these two coaxial cable types from the following image.
Besides, when using coaxial cable, you should remember that the impedance of the various devices being connected as well as the coaxial cable itself must match. For instance, connecting a 75 Ohm video camera connection to a studio monitor, the coaxial cable must also be 75 Ohm and the connectors on the coaxial cable must be 75 Ohm in impedance, otherwise, a standing wave will develop(notes: a standing wave is a signal reflection that is essentially wasted). FS.COM provides a range of copper cabling, including, twisted pair cable, twinax cable, and coaxial cable, and we also have plenty of fiber patch cables in stock. If you have any requirements, please visit FS.COM.
