R&S SU 4200 Scheduled Maintenance
6125.0226.12.01 5.2
The step width (1 bit) for the adjustment is approximately 10 Hz. Adjust it
only in small steps and do not detune the TXCO to the extreme positions,
because the internal reference on the RF module could unlock here. (CBIT
error 315, see chapter
4.2.1).
Nominal value
TCXO f ±0.2 ppm (corresponds to ± 24 Hz at 120 MHz).
5.1.2 OCXO Adjustment (VAR.03)
Inspecting
the air intake
Inspect the air intake on the front panel for dust build-up and clean it if
necessary. The inspection interval depends on the environmental conditions
under which the transmitter is operated.
Note: Due to the long service life of the fan, no regular maintenance is
required here besides cleaning. The speed of the fan is monitored by
means of the continuous built-in test (CBIT), and a warning is promptly
generated (see chapter
4.2).
OCXO adjustment
Due to the natural aging of the crystal oscillator (OCXO), it is advisable to
check the frequency offset after the first year of operation and readjust it if
necessary. We recommend a further adjustment interval of 3 years in order
to ensure the specified frequency accuracy.
Note: If the radio is started at low temperatures (approximately −20 °C), the
frequency of the OCXO is far from its nominal value. This causes the
generation of the CBIT message 315 TX INT REF UNLOCK. When the
OCXO is warmed up, this message will disappear. This is a typical behavior
of radios with the OCXO installed and not an indication of a radio failure.
This chapter
Test connection
Fig. 5.2 Test connection of OCXO adjustment
Test procedure
DUT is controlled via the R&S ZS 4200 (see chapter
3.3).
The minimum warm-up time is 10 minutes for the OCXO, the OCXO
OVEN WARNING has to be disapproved.
Test frequency: 120 MHz (see chapter
3.4.7.2)
Power level set: Low (see chapter
3.4.7.2)
Mode: AM (see chapter
3.4.7.2)
Radio is keyed ON, e.g. via function Test PTT, which delivers an
unmodulated SW signal (see chapter
3.4.7.4.1).
Measure frequency at antenna X3 and adjust OCXO value using
the R&S ZS 4200 (see chapter
3.3).
The step width (1 bit) for the adjustment is approximately 0.5 Hz. Adjust
it only in small steps and do not detune the OCXO to the extreme
D.U.T.
X3
ATT
30 dB
Spectrum
analyzer/
frequency
counter
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