52
CALIBRATION
The procedures listed in the following section allow the adjustment of
the FS700's bandpass filters, notch filters, and coarse adjustment of the
internal crystal oscillator. These are the only adjustments necessary to
completely calibrate the FS700. These calibrations should be rarely, if
ever, needed.
Note
: All or any part of this calibration procedure may be performed.
Necessary Equipment
The following equipment is necessary to complete the FS700
calibration. The suggested equipment or its equivalent may be used.
1) 100 MHz Oscilloscope
2) Synthesized sweepable function generator, 50 ohm output, 1 mV
minimum amplitude, such as Hewlett-Packard 3325B.
3) Precision Frequency Counter with at least 1 x 10
-9
resolution, such
as SRS SR620.
4) Antenna Input Termination Adapter. Schematic is shown in
TROUBLESHOOTING section Figure 1.
Coarse Oscillator Adjustment
There are two ways to adjust the oscillator. The first method requires
that the FS700 be locked to a LORAN station. The second method
requires a 10 MHz frequency source known to be accurate to better
than 5 x 10
-9
.
Note
: The FS700's oscillator should be on and warmed up for at least
1 hour prior to performing this procedure. Do not adjust the oscillator if
it is already within 5 x 10
-8
of 10 MHz (when locked the DAC value is
less than 10000).
Procedure 1:
1) Lock the FS700 to a LORAN-C station.
Note
: The next four steps must be done quickly, be familiar with the
procedure before starting.
2) Measure the 10 MHz output frequency on the counter. Record the
number.
