RF over fibre FAQs

RF over fibre FAQs

How do PPM RF over fibre links work?

PPM links can transport signals up to 1km with negligible degradation of signal-to-noise or frequency response – for example EMC testing or monitoring in hazardous environments. An RF signal is amplified, conditioned, and converted to the optical domain for transmission over fibre. At the receiver, an optical signal is converted back into an electrical signal – therefore a point2point link is transparent in any system.

What is the difference between Sentinel 3 and point2point?

Sentinel 3 is an intelligence RF over fibre system which allows for multiple-inputs and variable gain. Point2point RF over fibre links are simple, single-input, fixed (calibrated) gain links.
A Sentinel system also incorporates ‘smart’ features such as automatic temperature compensation, self-test, remote battery control (e.g. remote power up/down) link gain monitoring and control. Sentinel 3 has multiple connectivity options such as multi-core cross-site cables, breakout boxes and multi-channel Rx and Tx units. It is designed for complex applications, e.g. EMC testing of aircraft, buildings and vehicles. point2point links do not have the wide range of additional features that Sentinel offers.

Typical Applications:

    • Sentinel 3 – Aircraft EMC (e.g. LLSF, Lightning, NEMP), EMP testing of facilities, high power RF test
    • point2point (AC modulated links) – Land based platform testing, EMP facility test, RF distribution in particle physics
    • point2point (DC modulated links) – Circuit breaker testing, ABS EMC test

What is the difference between AC modulated links and DC modulated links?

AC and DC modulated point2point links perform the same function but (i) cover different frequency bandwidths and (ii) are designed for different signal levels. AC-modulated links use intensity modulation whereby an input signal is “mapped” from the electrical to the optical domain – i.e. same amplitude, different domain. DC links convert the input into a 14 bit digital signal before optical conversion. The digitisation allows very low frequencies to be transported. AC links are designed for small signals, typically less than 170 mVrms or 0 dBm and have 50 ohm inputs and outputs to match standard RF systems. DC links are designed to handle larger input signals, up to +/-150 V but have a high impedance input, like an oscilloscope. The DC output is designed to drive a 50 ohm load.

What frequency ranges/bandwidths are available?

AC links are available up to 3 GHz:
• 40 Hz to 250 MHz (G series)
• 2 kHz to 1.35 GHz (K series)
• 1 MHz to 2 GHz (P series)
• 10 MHz to 3 GHz (S series)

DC links are available up to 40 MHz:
• 0 Hz to 2.5 MHz
• 0 Hz to 20 MHz
• 0 Hz to 40 MHz