hf transceivers must be protected against overload due to reflected rf power that may occur in the case of mismatch to the antenna and may destroy the output stages. the usual transmitter power control using broadband directional couplers as sensors can often not be employed, however, since backdoor power components from neighboring transceivers activate the transmitter power control. as a result, transmitter power is reduced although there is no actual mismatch in the line under observation.
problems of this kind are likely to occur in applications where antennas are closely co-sited (e.g. collocation on board ships), or frequency spacing is very small, and especially in broadband systems where the amplifier outputs are directly connected with one another via 3 db couplers.
the new hf transceivers with selective level control feature narrowband evaluation of the forward and reflected power at the wanted frequency so that transmitter power control is not affected by rf power coupled in from other transmitters in the system.
the selective level control option can be employed both in the desktop and in the rackmount models of the r&s®xk2500l and r&s®xk2900l hf transceivers.
the r&s®xk2500l and r&s®xk2900l transceivers are equipped with selective sensors and feature the following benefits:
- 80% of the output power for vswr = 2
- no power reduction in case of signals fed in from other transmitters and δf ≥5% with 100 w backdoor power
- alc with digital signal processing