Specifications

5-20 888-2857-001 5/9/13
WARNING: Disconnect primary power prior to servicing.
Section 5 Maintenance and Alignments
Platinum VAX-C Series
5.6 Changing Frequency
This procedure describes manual change of the channel frequency to a new value. Save
the settings on the initial channel before proceeding with frequency change. Once
operation on the new frequency has been established, a second set of settings should
also be saved. This will greatly facilitate changing between frequencies in the future by
simply duplicating the previously recorded settings. The settings can be saved using the
web browser and navigating to Tx Home>Exciter Home>Setup>ISP>Save Settings.
This discussion assumes that the frequency will be changed manually and somewhat
infrequently.
Required Tools:
• Spectrum Analyzer
• Network Analyzer (use for re-tuning of output filter and determination of
coupling values)
• Directional coupler and average power meter or other precision power
measurement means. This is only required if the user would like to do a
power calibration at the new frequency, but it is not required.
!
CAUTION:
COAXIAL DIRECTIONAL COUPLERS MAY NOT BE COMPENSATED VERSUS
FREQUENCY. THAT IS, THEY WILL EXHIBIT A MONOTONIC RISE IN COUPLING
VALUE ACROSS THE VHF BAND. ACCORDINGLY, ANY COUPLING VALUES
WRITTEN ON COUPLER PORTS MAY NOT BE APPLICABLE TO A NEW OPERATING
FREQUENCY. CONSULT COUPLER FACTORY TEST DATA SHEETS (IF
FURNISHED) OR RE-MEASURE THE COUPLER WITH A NETWORK ANALYZER TO
DETERMINE THE COUPLING VALUES AT THE NEW FREQUENCY.
The caution above does not apply to internal VAX-C power measurements, which
are frequency compensated.
Procedure:
STEP 1 Turn off transmitter via OFF button on VAX-C front panel.
STEP 2 Use the LCD and front control buttons to navigate to POWER>LINEAR
and select BYPASS. Then navigate to POWER>NONLINEAR and
select BYPASS.