600 Chapter11
RF Section
A15 RF Assembly
level should be approximately −22 dBm.
7. Move the A2 controller assembly WR PROT/WR ENA jumper to the
WR ENA position.
8. While measuring the signal at the mixer 10.7 MHz IF output, adjust
the signal source until the level of the 10.7 MHz IF is −40 dBm.
9. On the HP 8560E/EC, press
SGL SWP, CAL, IF ADJ OFF, MORE 1 OF 2,
and
FLATNESS. Increase the gain of the flatness compensation
amplifiers to maximum by entering 0 using the data keys. This sets
the gains in the flatness compensation amplifiers to their maximum
values.
10.Connect the other spectrum analyzer to A15J601 and measure the
10.7 MHz IF signal level. The signal should measure greater than
−10 dBm. If the signal level is incorrect, continue with step 13.
11.Enter 4095 into the HP 8560E/EC Flatness Data. The signal level at
A15J601 should measure less than −36 dBm. This sets the gain of
flatness compensation amplifiers to a minimum. If the signal level is
incorrect, continue with step 13.
12.Check that the gain stages are properly biased and functioning.
13.Check the attenuator stages and flatness compensation control
circuitry.
a. For minimum gain (flatness data equals 4095), RF GAIN
(A15U909 pin 10) should be at −1.6 Vdc and the current through
each section as measured across R667 or R668 should be about 7
mA.
b. For maximum gain (flatness data equals 0), RF GAIN (A15U909
pin 10) should be at approximately 0 Vdc and the current through
each attenuator section should be close to 0 mA.
CAUTION As long as the flatness data just entered is not stored, the
previously-stored flatness data will be present after the power is cycled.
14.Move the WR PROT/WR ENA jumper on the A2 controller assembly
to the WR PROT position.
15.Reconnect the cable to A15J801.
Flatness Compensation Control
Refer to function block G on A15 RF Section schematic in the HP 8560
E-Series Spectrum Analyzer Component Level Information.
The flatness compensation control consists of a buffer amp (U909C) and
two identical voltage-to-current converters (U909B and U909D). The
thermistor RT901 in the buffer amp provides temperature
compensation for the PIN diodes in the gain stages and the SAW filters.
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