R&S^®Automatic VHF/UHF Filters

• Automatically tuned
• Medium RF power
• Medium selectivity
• Bypass for distress frequencies
• Stationary and mobile use

Design and features

This filter series has outstanding features such as:

• Compact 19" design, 3 HU
• Combined VHF/UHF type available
• Integrated bypass for receiving VHF, UHF or VHF/UHF distress frequencies

A combined VHF/UHF Filter R&S FT213A includes two capacitively tuned coaxial resonators per frequency range to form a two-section filter for the operating frequency. Tuning is carried out by means of a common[1] axle which is driven and controlled by a microprocessor-controlled stepping motor by way of a gearing. Following a frequency change input from the radio, the filter tuning axle is first driven to the normal start (HOME) position. It is then moved to an angular position corresponding to the new frequency.

The tuning is supported by a sophisticated and optically assisted motor control. If the frequency change is less than 100 kHz, retuning does not take place. The emission of RF power during the automatic tuning process is prohibited.

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, supported by the integrated scales and tuning control meter.

The robust design and the use of selected temperature-stable materials and lowloss (silver-coated) surfaces warranty the specifications:

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

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

Bypass benefits

The 121.5 MHz bypass or 243 MHz bypass (VHF or UHF guard receiver bypasses) bridges the guard frequency across the receiver by active extraction. During transmit operation the bypass is disabled electronically by means of control information from the radio. Thus distress channel reception is possible automatically without any manipulations.

[1] Common for the 2 resonators per frequency band and for VHF and UHF.