Nautel NX400, Installation Manual

Page: 50 / 89

NX400 Installation Manual Adjusting the spark gap
Issue 1.0 2017-06-30 Page 7-1
Section 7: Adjusting the spark gap
The NX400’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.
NOTE
:
Nautel presets the spark gap for 0.417 inches, which corresponds to a site altitude of 0 m (i.e,
sea level). If your transmitter site is at sea level, no spark gap adjustment is required.
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 NX400 Operations and Maintenance Manual for instructions on using the ac disconnect
switch, which is provided by Nautel.
3. Gain access to the RF output spark gap, by opening the front door of the output cabinet
(cabinet 3) and then opening the hinged filter panel, noting that it is secured using 23 M5
screws. Retain hardware.
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 0.417 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 and secure the filter door using M5 screws retained from Step 3 .
WARNING:
THE AC VOLTAGES PRESENT IN THE TRANSMITTER CAN BE FATAL. EXERCISE
EXTREME CAUTION.