R&S^®Automatic VHF Filters

• Automatically tuned
• High RF power
• High selectivity
• 4 ports or less

The Filters R&S FU221 and R&S FD221 are made up of two coaxial resonators, fixed-coupled to form a compact two-section filter plug-in. Tuning is performed manually by altering the length of the longitudinally adjustable inner conductors via a gearing common to both resonators.

The gear is driven by a microprocessorcontrolled stepping motor. Following a frequency change input from the radio, the inner conductors of the cavity resonators are first driven to their start (HOME) position in mechanical mid-position. Subsequently, the automatic tuning is continued by counting the frequency-specific definite angle of rotation of the stepping motor which is supported by a sophisticated and optically assisted motor control, electronically stored frequency characteristic and built-in tests. Two light barriers prevent the filters from moving against the two stops. From the gear unit, an additional axle is routed outward on which a manual tuning knob can be fixed in the event of automatic tuning failure.

The robust and mechanically stiff layout and the use of temperature-stable material for filter bodies, spindles and coupling in connection with silver-coating warranty the specifications:

• throughout the entire temperature range and
• under 100% duty-cycle high-power operation

The control cable between filter and radio unit provides the operating DC voltage as well as necessary frequency and other control information.