Local Oscillator - Kenwood TS-590SG Manual

03 LOCAL OSCILLATOR

In the first local oscillator, instead of employing the usual PLL/VCO system, the output of a DDS (Direct Digital Synthesizer)
is supplied directly to the mixer. As the oscillator frequency during down conversion is lower than it is during up-conversion,
better C/N characteristics can be obtained. This improves the reciprocal mixing characteristic resulted from the large input
signal near the received signal.
Reciprocal Mixing Characteristic (14.2 MHz, CW, BW: 500 Hz, PRE OFF)
Mistuned Frequency
2 kHz
10 kHz
50 kHz
Figure 3-1 DDS IC AD9951
Figure 3-2 C/N Characteristics of the First Local Oscillator
Reciprocal Mixing
94.7 dB
112.7 dB
120.2 dB
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