HP 8340A, Руководство по обслуживанию

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8-10
Model 8340A - Service
HP 8340A OVERALL INSTRUMENT THEORY
INTRODUCTION
Refer to Figure 8A-2, HP 8340A Block Diagram.
The HP Model 8340A is a synthesized sweeper that covers the frequency range from 10 MHz to
26.5 GHz in five bands. These bands are:
•
Band 0 (10 MHz to 2.3 GHz)
•
Band 1 (2.3 to 7.0 GHz)
•
Band 2 (7.0 to 13.5 GHz)
e
Band 3 (13.5 to 20.0 GHz)
•
Band 4 (20.0 to 26.5 GHz)
Internal to the HP 8340A are 7 phase-lock loops, 16 high frequency microcircuits, and a 16 bit
microprocessor. these provide the capability ofbroadband sweeps and the frequency accuracy of
a high-performance synthesizer.
REFERENCE LOOPS
The HP 8340A's frequency accuracy and stability are tied to either the 10 MHz internal
frequency standard or an external 10 MHz source. The Reference Loop uses this 10 MHz source
to generate all of the translation and reference signals that are used by other phase-lock loops
inside the instrument. These signals are:
•
400 MHz and 20 MHz signals used in the M/N Loop to produce the M/N output frequency.
e
10 MHz and 100 MHz signals used as reference signals in the 20-30 Loops.
•
A separate, lower power 100 MHz output sent to the RF Section for phase locking the 3. 7
GHz Oscillator to the 10 MHz Reference.
M/N LOOP
The M/N Loop produces an output between 177-197 MHz. This M/N output drives a Sampler in
the YO Loop. The variables "M" and "N" are integers generated by the processor and control
the output frequency of the M/N Loop. The output from the Sampler in the YO Loop must
always be between 20-30 MHz for the instrument to phase-lock. With the YO at a specific
frequency between 2.3 and 7.0GHz there will be an M/N output frequency between 177 and 197
MHz. When a harmonic of this frequency is mixed with the YO frequency in the Sampler, an IF
output between 20-30 Mhz will result. the Sampler output is then compared to the 20-30 Loop
output by the YO Loop Phase/Frequency detector in the YO Loop.
20-30
LOOPS
The 20-30 Loops contain 3 phase-locked loops that are used in conjunction with one another to
provide the HP 8340A YO Loop with 1 Hz CW resolution, and with analog sweep widths from
100 Hz to 5 MHz. For sweep widths <5 MHz the YO Loop remains phase-locked during the
sweep, and the 20-30 Loop is swept the desired amount. For sweep widths
>
5 MHz, all phase­
lock loops lock at the beginning of sweep, the 20-30 Loop remains fixed, and the YO is swept.
This is called Lock and Roll and will be discussed later.
Scans by HB9HCA and HB9FSX