Comparing Fibre to Copper
Cable System Costs

The introduction of fibre cable in the broadcast facility has given the broadcaster unprecedented technical advantages to implement a wide range of signal distribution possibilities both now and in the future. But what about the economic differences when compared to traditional coaxial distribution? Is fiber less expensive, making it attractive both economically and technically?

The Cost of the Cable

First, let's look at the cost of the raw cables. Looking at typical published prices in the USA for a single core of PVC jacketed single mode fiber, we find that $0.23/meter is about average. Broadcast quality RG-6/U coax cable, suitable for HD-SDI, costs about $1.92/meter or over 8 times more! Considering how many thousands, if not tens of thousands, of meters of cabling can be used in a broadcast facility the savings can be quite large.

But wait, it gets better.

Consider that fiber is typically purchased in multi-core bundles where multiple fibers are placed under one jacket. Unlike coax, only the actual glass core needs to be replicated under the jacket, not the entire construction of the fiber cable. In a 12-core fiber bundle, the cost per core drops to about $0.092/meter, or about 20 times less than coax per core.

The Size of the Cable

The most common size of a PVC jacketed single core single mode fiber is 2.9mm in diameter. In comparison, HD-SDI quality RG-6/U as an example is 6.96mm, or 2.4 times wider. The 12-core fiber bundle has a diameter of only 6.5mm compared to a bundle of 12 coax RG-6/U cables of about 26mm. The result is that for fiber we can use smaller diameter conduits and cable trays. Additionally, we do not have to worry about deforming the fiber bundle with tie-wraps, which needs to be avoided when working with coax at high data rates.

Considering the difference in weight between fiber and coax, fiber is over 6.5 times lighter than coax. 2.9mm single core fiber weighs in at about 9 grams/meter. RG-6/U coax is 61 grams/meter. A significant difference, which can save a lot of money on structural costs when coupled with lower physical size.

But what about bend radius? There seems to be a common misconception that fiber cables must have a very wide bend radius, presumably so that the glass inside the cable won't break. Well, that's just not true. The rule of thumb with fiber cables is that the bend radius can be about 10-11 times the diameter of the cable. Using our 2.9mm fiber as an example, we have a bend radius of about 32mm. Now compare that to the bend radius of RG-6/U HD-SDI coax which is 70mm, or almost 2.2 times wider.

The Bandwidth of the Cable

Bandwidth costs money. For any medium, wired or wireless, it is a simple truth. You can compress a signal to require less bandwidth but the process of compressing the signal adds cost to the equipment and decreases the signal quality. In many cases, this is counterproductive.

The bandwidth or frequency response of any coaxial cable is usually well documented by its manufacturer. The variables that determine the useable length are the bandwidth of signal being communicated and the amount of signal attenuation and distortion that can be tolerated by the load at the end of the cable. The better the bandwidth of the coax cable the longer the useable length and the less signal attenuation and distortion will result.

For single mode fiber, as a practical matter in broadcast, we almost never factor in the bandwidth of the fiber. Given today's technology, the useable bandwidth is limited not by the fiber but by the electronic devices at either end of the cable. We must, however, take into account the attenuation of light as a function of length but this can usually be overcome by increasing the launch power of the laser at the source or by the use of active repeaters within the cable distribution structure. In today's broadcast facilities, the length of even the longest fiber segment does not impose enough attenuation of the light to require higher than standard powered lasers or mid-segment active repeaters.

One last word on the bandwidth of fiber compared to coax. On single mode fiber we can easily multiplex multiple wavelengths of light onto one fiber core, even at very high data rates. Consider the aggregate savings in cost using just one 2.9mm single mode fiber to communicate 16 uncompressed 3G/HD/SD-SDI signals either within a broadcast facility or cross-town! Try that with coax.