HP 8340A Service Manual page 270

INTRODUCTION
The major function of the A58 sweep Generator board is to
generate three voltage ramps:
20-30 SWP (TP8). VSWP is the ramp voltage that will sweep the YO
over the frequency range of interest. When the 8340A is set for a
sweep width of greater than or equal to 500 KHz and the entire
sweep is contained on one band,
generates the voltage that tunes the YO to the start frequency of
the sweep. VSWP is then summed into the PRETUNE voltage.
zero volts at the beginning of the sweep.) Next the 8340A
acquires phase-lock at the start frequency. When the sweep is
initiated, the YO error voltage
the A49 YO Loop Phase Detector,
duration of the sweep. Finally the loop is opened,
allowed to ramp up and sw�ep the YO from the start frequency to
the stop frequency. Thus the PRETUNE voltage always corresponds
to the YO frequency. This type of sweep scheme is called lock and
roll.
When the sweep is contained in two or more multiply bands,
8340A re-phase-locks the YO and VSWP resets to zero at each
bandcrossing. Thus,
voltage to sweep the YO from the last phase-lock frequency
frequency or last bandcross frequency) to the stop frequency or
the next bandcross frequency,
VSWP has a sensitivity of +2 volts/GHz of YO frequency. The
distinction between YO frequency and instrument frequency
important because the instrument frequency is not necessarily the
same as the YO frequency. In the
the YO output is heterodyned with a 3.7 GHz oscillator.
Consequently, the YO frequency in this case is 3.7 GHz higher
than the instrument frequency.
In the higher bands
instrument frequency is derived from the first,
fourth multiple of the YO frequency as shown in Table 8D-3 below.
Model 8340A - Service
A58 SWEEP GENERATOR
VSWP (TPlO),
the A54 YO Pretune board
(YO TUNE) is sampled and held by
and it remains constant for the
in the multi-band case,
whichever the case may be.
10 MHz to 2.5 GHz band
(SYTM multiply bands 1 through 4),
Scans by HB9HCA and HB9FSX
MKR RMP (TP4), and
(VSWP is
and VSWP is
VSWP provides the
is
(Band 0),
the
second, third,
the
(start
or
8-357