FREQUENCY CHANGE INSTRUCTIONS MX

FREQUENCY CHANGE INSTRUCTIONS
MX-15 EXCITER
Equipment List.
1.
2.
3.
4.
5.
6.
7.
8.
Audio Generator
Distortion Analyzer capable of measuring IMD.
Modulation Monitor
Line Sampler or Directional Coupler with a voltage
sample output capable of driving the modulation monitor
and frequency counter.
50 watt dummy load.
Bird Wattmeter with 25 and 5 watt elements.
RF spectrum analyzer.
Frequency Counter
A.
AFC Programming
Strap the frequency divider circuit in the AFC module
for the proper frequency using the frequency program
chart on page l3 in the AFC section of the instruction
book.
B.
Modulated Oscillator Adjustments
Put the Modulated Oscillator on the extender board.
Connect the exciter RF output through the Line Sampler
or Directional Coupler to the 50 ohm dummy load. Apply
A.C. power to the exciter. Depress AFC on the
Multimeter switch. Tune AFC voltage adjust (C3) for an
AFC voltage as near to 7 volts as possible on the
Multimeter. Check for AFC lock in five (5) seconds.
At the top or bottom of the band, if the AFC won't
lock, try adjusting the voltage a bit lower than 7V.
Connect the frequency counter to the line sampler or
the directional coupler forward port. Adjust frequency
adjust control (Rl8) on the front of the AFC module for
the exact carrier frequency.
With the Modulated Oscillator still on the Extender
board, apply one (l) volt RMS (2.83Vp-p) at lkHz to the
composite input jack, (J4) on the back of the exciter.
With the modulation switch in the B-Band position,
adjust the B-Band level control (R25) on the Modulated
Oscillator for l00 percent modulation reading on the BBand Meter on the exciter. Adjust the VCO Gain Control
(R52) for l00 percent modulation reading on a separate
modulation monitor as read through the RF Line Sampler
or Directional Coupler forward port. Disconnect the
signal from the COMPOSITE INPUT (J4) on the rear of the
exciter and apply a 2.83v P-P SMPTE intermodulation
MX-15
test signal into J4. Connect an intermodulation
distortion analyzer to the modulation monitor composite
output or the audio output with the de-emphasis
disabled. Adjust the Distortion Null Control (R74) for
minimum intermodulation distortion (less than .02%).
C.
RF Amp Adjustments
Connect a spectrum analyzer to the line sampler or
directional coupler forward port. Using the spectrum
analyzer, adjust C3l for minimum amplitude of the
second harmonic. The harmonic must be -53dB down from
the carrier reference.
Connect the exciter RF output to a 50 ohm load through
an accurately calibrated wattmeter capable of measuring
forward and reflected power.
Switch the AGC control to ON. Adjust the wattmeter to
measure forward power and adjust the OUTPUT ADJ control
(Rl3) to obtain a l0 + 0.l watt indication on the
external wattmeter.
Do not use the extender board. Alternately remove and
replace the RF AMP module from the exciter while making
these calibration adjustments.
Depress the MULTIMETER FWD PWR switch and calibrate the
FORWARD power adjust (R47) until the indication matches
the external wattmeter indication.
Pull out the MOD OSC module and the carrier should be
muted. Note: Multimeter indication in FWD PWR.
Insert the MOD OSC and the carrier must remain muted
until the AFC/PLL locks. (4.5 seconds).
Disconnect RF output cable from J3 on the rear of the
exciter.
Adjust VSWR threshold control Rl8 to set the MULTIMETER
FWD PWR indication to five (5) watts.
Switch to REF PWR range and adjust reflected power
calibrate(R37) on the RF AMP for the same indication as
read on the FWD PWR range.
Re-connect the output cable to the 50 ohm load.
The
Multimeter must indicate less than or equal to 0.5
watts on the REF PWR range.
This completes the MX-15 frequency change.