448 Chapter8
IF Section
A5 IF Assembly
3 kHz and 10 kHz Resolution Bandwidth Problems
Asymmetric Filter Response: Check the crystal symmetry control with
the following steps:
1. Press
PRESET.
2. Set the spectrum analyzer controls as follows:
Resolution bandwidth ................................................3kHz
Span ........................................................................100kHz
Center frequency .................................................. 300MHz
3. On the spectrum analyzer, connect the 300 MHz CAL OUTPUT to
the INPUT 50 Ω.
4. A trace similar to Figure 8-15 on page 448 indicates a failed
crystal-symmetry circuit.
Narrow 10 kHz resolution bandwidth: Check for printed-circuit board
contamination. Clean the board as required.
IF Gain Compression in 10 kHz resolution bandwidth: FET transistors
Q202, Q203, Q501, and Q503 can deteriorate with age. Measuring less
than 0 volts on the FET source indicates a bad FET.
Figure 8-15 Faulty Crystal Symmetry
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