HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

The Last Converter has three main purposes:

1. Converting the 321.4 MHz IF signal from the A6 RF Module down to 21.4 MHz for

processing by the IF-Display Section.

2. Providing the means for correcting for variations in conversion loss versus frequency in the

input circuitry.

3. Filtering out 278.6 MHz image response.

The Last Converter consists of 11 basic elements. They are a 321.4 MHz amplifier, a 321.4
MHz 

 filter, a 321.4 to 21.4 MHz converter a 21.4 MHz preamp, two pin diode

attenuators, two pin diode controlled variable gain amplifiers, an output stage, a temperature
compensation circuit, and power supply filtering.

The power supply filtering consists of series inductors and shunt capacitors (L21 to L24
and C49 to C53). In addition to this, R38 and 

 provide a 6.2 V source used for biasing

transistors.

The 321.4 MHz amplifier consists of Q8 and its associated circuitry. Q7 provides bias for 
by setting the base current.

The 321.4 MHz amplifier drives the 321.4 MHz 

 filter which consists of L4 to L8

and C8 to C12. This filter is made up of five LC tank circuits coupled magnetically and
capacitively. Capacitive coupling occurs through PC board traces on the circuit side of the PC
board. Coupling into and out of the filter is done with tapped inductors L4 and L8. The filter

is tuned by means of C8 to C12. This filter rejects the 278.6 MHz image response.

The 321.4 MHz filter drives the 321.4 to 21.4 MHz converter. This converter consists of a
packaged double-balanced mixer, 

 The 300 MHz LO for this converter comes from the

 Phase Lock.

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