FREQUENCY PRESELECTORS WITH TUNABLE FILTERS (Y.I.G.)
In the web section "Frequency Preselectors with Filter Banks" we analyzed some applications requiring one or more external filters use.In most of the cases this solution is sufficient to fix intermodulation issues, however if a very broadband range need, the use of a tunable preselector is more appropriated
Like in a spectrum analyzer front end, a tunable filter is obtained by using a special device called Y.I.G.S. (Yttrium Iron Garnet Spheres -see Figure 2).By controlling the component current loop it is possible tuning the filter over a very large frequency range, from a few hudred MHz to several GHz. The filter shape remain the same, while just the central frequency is moved over octaves or multioctaves. Generally a cascaded low noise amplifier is always desiderable to recover filter and cable losses. Typically the YIG filter losses are not negligible and quantifiable in 5-7 dB, depending from the type used. In the assembly we consider about 10 dB, due the internal semirigid path losses.
Frequency tunable preselectors can be fit in a outdoor sealed case ot in a classic benchtop case either. The outdoor type is powered and controlled by an external control box.
Please consider this are just examples of some frequency available. We could design tunable preselectors up to 40 GHz on demand.