t.1.1. Measuring the Bandpass Filter Response (Simple Method)
The simplest approach to measuring the response of the bandpass filter is as follows:
Test Setup SB-102: Measure RF Signal at Driver Output jack on the rear panel.
Remove the 6146 Screen voltage by removing MOLEX plug on rear. This makes it
easier on the finals while performing the measurements. Switch to TUNE mode and
Peak the DRIVER/PRESELECTOR for maximum signal level at each measurement
point.
Test Setup SB-101 & HW-101: Measure RF Signal at CR-201 (located near 100 KHz
XTAL) Anode (non-banded end). It is recommended to remove 6146 Screen voltage by
disconnecting R920 (100 ohm to Pin 3 on 6146s). This makes it easier on the finals
while performing the measurements. Switch to TUNE mode, Peak the
DRIVER/PRESELECTOR for maximum signal level at each measurement point.
Connect an oscilloscope or VTVM with an RF probe to the Driver Output connector on
the rear panel and measure the level as the LMO is tuned from end to end. It is
necessary to peak the Pre-Selector/Driver control for each measurement.
By recording the signal value at multiple points (e.g., every 50 KHz), it is possible to
construct a graph of the frequency response.
t.1.2. Measuring the Bandpass Filter Response (Sweep Analysis)
If a sweep generator and oscilloscope with an RF demodulator probe or spectrum
analyzer with tracking generator is available, the bandpass circuitry can be swept to
visually determine the frequency response.
Two different setups are required, one for receive mode and a second for transmit
mode.
Alignment Page 41
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