Nautel NX300, Installation Manual

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NX300 Installation Manual Adjusting the spark gap
Issue 3.0 2012-11-01 Page 7-1
Section 7: Adjusting the spark gap
The NX300’s RF output filter contains a spark gap that must be adjusted - based on site altitude - to
provide protection against excessive voltage (i.e., lightning) on the RF output.
If the altitude of the transmitter site is known prior to transmitter delivery, then the spark gap is
adjusted at Nautel. If this is the case, it may only be necessary to verify the spark gap setting.
1. Determine the altitude of the transmitter site (in feet).
2. Make sure that the ac power is switched off and locked out. Refer to the Operating section of
the NX300 Operations and Maintenance Manual for instructions on using the ac disconnect or
safety interlock switch, which is provided by Nautel.
3. Gain access to the RF output spark gap, noting it is in the top section of the output cabinet
(Rack 3).
4. Locate the spark gap (see Figure 7.1 on page 7-2 ). Using a feeler gauge, measure the air gap
between the spark gap balls.
5. The air gap should be 0.407 inches multiplied by the scale factor listed in Table 7.1, “Altitude
Scale Factor” on page 7-3 for the altitude determined in Step 1 . If not, loosen the locking nut
on the bottom carbon hemisphere, adjust the position of the spark gap ball for the required
gap and then tighten the locking nut.
6. Close the filter door using the M5 screws retained in Section 3, “Completing cabinet
assembly” on page 3-1 .
WARNING:
THE AC VOLTAGES PRESENT IN THE TRANSMITTER CAN BE FATAL. EXERCISE
EXTREME CAUTION.