What is an analog RF over fiber link and when would I use it instead of a coaxial cable run?
Analog RF Over Fiber Links
RF over fiber technology has become essential infrastructure for distributed antenna systems, radar remoting, satellite ground stations, and electronic warfare signal transport.
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
Frequently Asked Questions
When should I use coax instead of fiber?
Coaxial cable is preferred when: the distance is short (< 30 m at microwave frequencies, < 100 m at HF/VHF). The link noise figure must be very low (coax NF = cable loss; fiber NF = 20-40 dB). The cost must be minimal (RFoF modules cost $500-5000 per link; coax cable costs $5-50/m). Wideband dynamic range is not critical. Below 1 GHz and < 50 m: coax is almost always the better choice.
Is digital fiber better than analog?
Digital RFoF (digitizing the RF signal and transmitting digital data over fiber) offers: better dynamic range (limited by ADC/DAC resolution, not laser linearity), immunity to fiber nonlinearities, and ability to multiplex many channels on one fiber. However: it adds latency (ADC/DAC conversion time: 1-10 μs), requires high-speed ADCs/DACs (which are expensive and power-hungry), and adds quantization noise. Analog RFoF is preferred when: latency must be minimized (radar, EW), the signal bandwidth exceeds the ADC capability, and simplicity is important.
What about wavelength division multiplexing?
WDM (Wavelength Division Multiplexing) allows multiple RF signals to share a single fiber by assigning each signal to a different optical wavelength. CWDM (Coarse WDM): 18 channels at 20 nm spacing (1270-1610 nm). DWDM (Dense WDM): 40-80 channels at 0.8 nm spacing. Each channel carries a separate RF signal. This is used for: multi-element phased array remoting (one fiber per array face), distributed antenna systems (multiple sectors on one fiber), and multi-band receivers (each band on a separate wavelength).