The circuit shows a simplex fiber link between the NE5080 transmitter and the NE5081 receiver. The components shown are for a center frequency of 5 MHz, although this frequency can be increased to 20 MHz with proper selection of external component values. The NE5539 has a 530-MHz unity gain bandwidth which could limit maximum operatingfrequencies in some systems. Since the NE5081 can adequately accept signals below 10 mV at 5-MHz carrier, the gain stage within the dashed lines can be eliminated if the attenuation in the link is low.
If the gain stage is used, be mindful of the bandwidth trade off at higher gains. Refer to the NE5539 data sheet for details.