Get More Fiber (Optics)!

Welcome to Tech Talk, Pico Macom's series of technical notes, featuring useful information and equipment tips. This installment of Tech Talk discusses using Pico Macom fiber optic transmitter, receivers and optical nodes.

Is there an advantage?

Of course, there are tremendous advantages to using an all-fiber optic transport and distribution system. These are just some of them:

  1. As always, the number one factor in cost. The cost of raw materials to manufacture coaxial cable has significantly increased, raising the cost of the cable. On the other hand, the material used to make the glass for fiber cable—sand—is plentiful. So, with quantity comes cost reduction. Changes in the manufacturing process and the quantity of materials have lowered the cost of making glass fiber to a very affordable alternative.
  2. Fiber installation is easier. Glass is actually stronger than steel; the fibers are thinner and bend easier and tighter than hardline coax. After installation, fibers can be fused together, nearly eliminating the losses associated with manual splices and suckouts that occur as a result of temperature changes.
  3. The small diameter of a glass fiber—slightly larger than a strand of hair—allows many fibers to be bundled in the same space as a single coaxial cable. This enables cable operators to transport area-specific channel lineups and means smaller home count per fiber. In addition, greater use of the reverse band is achieved through a smaller number of homes served by a fiber.
  4. With fiber, wider signal bandwidths can be transported with less CTB/CSO distortion, which occurs with channel loading. The lower attenuation of fiber greatly reduces the number of amplifiers and power supplies required. Less equipment means less distortion, fewer failure points and lower maintenance costs.
  5. No voltage is carried on fiber optic cables. This ideally suits fiber for use in schools, hospitals and government buildings where fire codes are stringent and would require more expensive fire-retardant coaxial cables.
  6. Light is not susceptible to RF signal ingress/egress, while signals over coaxial cable can be compromised by loose connectors, cracked shielding and other factors.

Fiber Applications

Fiber optic cable lends advantages to many different architectures and system designs. A new design for trouble-free operation is fiber to the premise box. In an older system where an update is required, fiber can replace city-specific trunking applications or reduce amplifier cascades. In a newer system that may already employ fiber, node size reduction will divide homes using the return path so that cable modem speeds are increased.

This section will provide some simple connection diagrams as examples.

Headend to Hub
In one of the simplest steps for increased reliability, the point-to-point transport works well for 5~42MHz reverse path signals and equally well as for the 54~860MHz forward path. In one system, the city was serviced by a dual trunk 32 amplifier cascade. And that was just to get the signal from the headend to the city! It was later switched to a microwave link (introducing rain fade) then to a fiber link that performed flawlessly. It is so simple to connect.

  1. The headend output is connected to the PFT-** RF input.
  2. The cable is connected to the fiber output of the PFT-**. The other end of the cable is connected to the fiber input of the PFR-2.
  3. The PFR-2 RF output is connected to the distribution system.

Diagram 1

Headend/Hub to Node
This method of hybrid fiber/coax system is currently the most common. Utilizing the PFT-**, PON-4RX4 and PRR-4 provides the optimum functionality of the return system and requires five optical cables.

  1. The headend output is connected to the PFT-** RF input.
  2. A cable is connected to the fiber output of the PFT-**. The other end of the cable is connected to the fiber input of the PON-4RX4.
  3. Four cables are connected to the fiber return outputs of the PON-4RX4. The other end of the four cables are connected to the fiber input of the PRR-4.
  4. The PRR-4 RF outputs are connected to the headend return equipment.
  5. The four bidirectional RF ports of the PON-4RX4 are connected to the coaxial distribution system.

Headend/Hub to Premise Node
In many cases such as school, institutional, business and lodging applications, an indoor node or mini-node is desirable. This will allow a custom channel lineup and a dedicated return path. In many cases a higher power PFT-** would be used as well as optical couplers to divide the optical signal to multiple fibers. The indoor nodes provide a slightly lower output level. The main advantage of the indoor nodes is that they can be powered by the traditional 120VAC line outlet. To show this application we will assume a lower optical power level and skip the optical couplers.

  1. The headend output is connected to the PFT-** RF input.
  2. A fiber cable is connected to the fiber output of the PFT-**. The other end of the cable is connected to the fiber input of the PMN.
  3. A cable is connected to the fiber return outputs of the PMN. The other end of the return cable is connected to the fiber input of the PRR-2.
  4. The PRR-2 RF output is connected to the headend return equipment.
  5. The bidirectional RF port of the PMN is connected to the local coaxial distribution system.

Diagram 3

Using Pico Macom Fiber Optic Equipment is a snap!

Want To Know More?

PFT-**, PFR-2, PON-4RX4, PRR-2, PRR-4, PMN-1

The products mentioned above make installing and upgrading to a fiber optic system easy and efficient. These are just some of the many innovative products available from Pico Macom. Please visit our Web site at www.picomacom.com to see many other exciting new products. Or call us at 800-421-6511, and let our knowledgeable and courteous staff assist you with other Pico Macom products and applications.