30
kHz
Resolution Bandwidth Problems
Shape factor too high: Shape factor is the ratio of the 60 dB bandwidth to the 3 dB
bandwidth. Shape factor should be less than
15:l.
If one of the LC poles malfunctions, the
shape factor may be the only indication of the failure. Isolate the non-functioning pole with
the IF signature. Region E of Figure 8-8 illustrates the four LC- pole adjustments. Take
several signatures to examine the LC-pole adjustments. If one of the four sections of Region E
is consistently longer than the others, the corresponding LC pole is faulty.
IF gain compression: FET transistors Q301, Q303,
Q700,
and Q701 can deteriorate with age.
Measuring less than 0 volts on the FET source indicates a bad FET.
Bandwidth too wide: Check for contamination on the printed-circuit board. Clean the board
as required.
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:
RES BW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3kHz
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 kHz
FREQUENCY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
100kHz
3. On the spectrum analyzer, connect the 300 MHz CAL OUTPUT to the INPUT
500.
4. A trace similar to Figure 8-15 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.
8-32 IF Section
To Next Page
Loading...
Need help?
General
