Do you know what RF over Fiber is? Or Radio-over-Fiber-optic systems?
It is a technology that uses the advantages of Fiber optics in Radio frequency applications. It is the method of converting a radio wave (RF) into light by modulating the intensity of the light source (typically a laser) with RF signal. This is an analogue process, and no digitization is used.
The light signal is then transmitted over a Fiber optic cable, which replaces and exceeds the capabilities of traditional copper coax cable.
Fiber optic cable is not distance-limited like coax, you can extend the link distance up to a huge 600 km (373 mi) without compromising on signal performance. Look at the diagram below, to compare between coax loss and Fiber, when increasing frequency also look at the distances.
A typical RF over Fiber system will consist of the three main elements:
1. Optical transmitter.
2. Fiber optic cables.
3. Optical receiver.
The system is defined in terms of normal RF parameters, i.e. gain, noise figure, linearity etc., and can be treated as an RF black box by a systems designer.
How the system works?
1. Radio signals are modulated (impressed) onto a light carrier using an electrical-to-optical (E/O) converter.
2. The modulated light pulses travel through the Fiber optic cable with minimal signal loss.
3. At the receiving end, an optical-to-electrical (O/E) converter changes the light pulses back into radio signals.
Benefits?
* Very low signal loss – less than 0.5db/K, allowing for connections of several kilometres without the need for amplification.
* Reduced interference: Fiber optic cables are immune to electromagnetic interference (EMI) which can disrupt radio signals - due to Fiber being a non-conductive medium.
* Security against signal interception.
* Low maintenance: install and forget technology.
* Cost effective: compared to high end, low loss coax cable and slope compensation amplifiers.
Typical applications include:
1. Satcom ground segment equipment – such as teleports, broadcast facilities, VSAT gateways, etc.
2. Broadcast Production – including wireless cameras, microphones.
3. GPS for timing – timeservers, base stations and re-radiating
3. Maritime – GPS and Satcom
4. Cellular and timing – GPS, re-broadcasting and distribution
5. Mining and Public Safety – timing and communications
6. Telemetry – Satellite, missiles and spacecraft.