local oscillator for 2 m transceivers

7-90 — elektor julyiaugust 1981 local oscillator filter for 2 m transceivers One of the most useful improvements that can be made to an existing 2 metre transceiver is to be replace the dual-gate MOSFET mixer with a custom double balanced modulator IC. This will result in an improved noise figure and greater dynamic range. However, it is often forgotten that the local oscil- lator will have to meet more stringent demands on spectral purity (due to its switching action the double balanced modulator is much more prone to "spurii" than a linear mode MOSFET mixer). At the same time, the output level of the local oscillator L3 (and csw saturation level of around 20 dBm, being adequate for the majority of currently available double balanced modulators. Provided the circuit is constructed correctly, it should be possible to obtain the following specifica- tions: centre frequency = 134.7 MHz (aligned for region 1) bandwidth at —1 dB = 5 MHz bandwidth at —6 dB = 7 MHz bandwidth at â€...