Giga-tronics GT 9000, Operation & Maintenance Manual

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3.2.7 The Downconverter
Frequencies up to 2000 MHz are generated within the downconverter module. The 10 to
2000 MHz range of the downconverter spans more than seven octaves; in order to accommodate
changes in component frequency response across so wide a range, the module is divided into
multiple paths.
Frequencies in the range of 875 to 2000 MHz are generated as follows. The output of the 2 to
8 GHz YIG, tuned to a frequency in the range of 3500 to 8000 MHz, is applied (through a
switch) to a Divide-by-4 circuit. The Output PLL locks the YIG output to a frequency which is
four times higher than the desired output.
Frequencies in the range of 500 to 875 MHz are generated in almost exactly the same way,
except that a different Divide-by-4 circuit (with a lower input range) is used. In this band, the
YIG is tuned by the Output PLL to a frequency in the range of 2000 to 3500 MHz, and the
divider reduces it to the desired output frequency.
Frequencies in the range of 10 to 500 MHz are generated by downconversion (that is, by mixing
two high-frequency signals in order to obtain an intermediate frequency in a lower range). In
this band, the 2 to 8 GHz YIG is locked on 8005 MHz. The 8 to 20 GHz YIG is locked on a
frequency in the 8045 to 10005 MHz range (this frequency is set higher than 8005 by an
Figure 3-7. Downconverter module
Model GT 9000 Microwave Synthesizer
3-12
Manual No. 120AM00250, Rev C, September 1998