EIP 545A - Theory of Operation

THEORY OF OPERA'TION
The power meter uses the Schottky diode in the microwave converter as its power sensor. The output
of the diode detector
is connected to a programmable gain attenuator, which consists of two switchable
gain stages (one
is in the IF Amplifier A201B and one is on the Gate Generator A107) and two 8 bit
attenuators. A comparitor, set to 100
mV, and a TTL latch provide output information to the micro-
processor. See figure 02-1.
After the counter has
a signal, and has taken a frequency reading, it starts the power meter task. This
triggers the gate time counter, resets the TTL power latch, moves the yig +50 MHz (to insure that the
signal peak
is passed through), then checks the TTL power latch. If the latch is set, the attenuation is
increased in 3 dB steps ( until the signal is attenuated below the level of the comparitor), then back one
step. If maximum attenuation
is reached, and the latch is still being set, the word OVERLOAD is
displayed and the task is exited.
When the latch
is first checked, if it is still reset, the attenuation is decreased in 3 dB steps until the
comparator level
is reached. If minimum attenuation (maximum gain) is reached, the display is set to
EE.E, and the task is exited.
After the attenuation-is adjusted to
a 3 dB resolution a successive approximation is performed to find
the attenuation to
a 0.1 dB resolution. The attenuation is stored, and if the gate time counter is not
finished, the cycle
is repeated. When the gate time counter is finished all the readings are averaged to
eliminate the effects of AM on the signal.
INPUT
Wl
FILTER
PROGRAMMABLE
ATTENUATOR
1510dB 1510dB
GAIN INVERTING
STAGE
GAIN STAGE
0 mV
COMPARATOR r\
-TO A105
MICRO-
PROCESSOR
(for ZEROING)
SCHOTTKY
DIODE
DETECTOR
-
-
Figure 02-1. Power Meter Hardware
8 BIT
PROGRAMMABLE
ATTENUATOR
-(
0.1 dB
COMPARATOR
Scans by ArtekMedia © 2007