5. Conclusions

5.1 Simplified optical link model for transmission of a carrier

The model is based on the Spurious Free Dynamic Range graph :

Figure 2. RF frequency respone (for several RF input powers).

Thanks to this graph, it is possible for a given RF input power to determine :
  1. RF output power and related gain ;
  2. Output noise ;
  3. 3rd order intermodulation products.

It is possible to calculate Carrier to Noise, Carrier to Intermodulation and Carrier to Noise & Intermodulation ratio.

5.2 Link comparison : Optical link vs Coaxial Cable for 30 m link length (like in a home)

In the following table, there is a comparison between coaxial cable to optical link.

Parameter Coaxial Cable Optical Link
RF Gain @ 950 MHz [dB] -3.6 +0.5
RF Gain @ 2150 MHz [dB] -5.6 +3.0
Noise Figure @ 950 MHz [dB] +3.6 +30
Noise Figure @ 2150 MHz +5.6 +33
IIP3 [dBm] +50 +10
SFDR [dB/Hz2/3] +145 +102
LNB remote supply Yes, supplied through coaxial cable No, supply close to antenna for OTX required
Current Consumption [mA] 0 700 mA / 12 V
LNB telecommand Yes No
Bidirectional link Yes Yes, but with additional hardware
Cost Low High

For a distance of 30 m, optical link is not justified : performances and cost are not competitive with coaxial cable.