Electro-Metrics EM-2115, Инструкция по эксплуатации

Страница: 147 / 278

EM-2115 APPENDIX C FUNCTION AND DESCRIPTION
(EM2115C-8)
The selected IF output from the 0.1 Narrowband Module is applied through a successive
series of log detector stages to produce a DC-coupled reproduction of the logged envelope of the
IF input signal (AM Video signal). In addition, a limited IF signal is also produced.
The logged video signals from all three log circuits is applied through a single output
connector (A4J7) to the Detector Board (A8).
The limited IF signal produced by each log circuit is applied through separate output con-
nectors (through subminiature coaxial cables) to corresponding connectors on the Discriminator
Module (A5).
C-8.0 A8 Detector Board
(Refer to Figure H.16)
The Detector Board produces the Peak, Quasi-Peak, Average (Carrier), RMS, and
Slideback outputs. The board is divided into two subcircuits:
a. Quasi-Peak/RMS/Average Detector,
b. Peak Detector/Slideback.
The Quasi-Peak/RMS/Average Detector circuit detects the logged video signal to produce
a DC video output. This video output represents the log of the true RMS, Average, or Quasi-Peak
linearly detected signal, depending on the detector value selected.
In the Peak mode of the Peak/Slideback Detector circuit, a sample and hold circuit cap-
tures the peak signal level and holds this level for metering. The hold time is determined by the
setting of the front panel Sample Time Control. In the FULL CCW position of this control (click
stop), the sampling circuit is never reset. As the control is increased in a clockwise direction, the
detector is reset at an increasing rate.
In the Slideback mode of the Peak/Slideback detector, it is converted to a biased detector
with the bias level being determined by the front panel Slideback Control. The hold time for sig-
nal levels exceeding the bias level is short. The video output is AC couplied to the audio output
circuit, so that any signal exceeding the bias level can be heard in the earphones. The front panel
Digital Amplitude Display and analog meters read the DC bias level, so that the meters indicate
the equivalent input level (in dB(µV)) to which the bias is set. Using the Slideback (bias) Control
plus the audio signal in the earphones, the level of a signal can be measured (Audio Extinction
Technique).