Marti RPT-30, User Manual

Page: 22 / 43

sampling attenuator. Place CONTROL switch in
“TRANSMIT” position.
1. Measure bias voltage at TP (test point) of MODULA-
TOR BOARD, 800-160 using sensitive DC voltmeter.
This voltage should be between 4.5 and 5.8 volts DC.
2. Set transmitter on frequency by adjusting L1 with
FREQUENCY switch in “F1” position. If necessary,
coarse adjustment can be made using L2 (for F1) and L3
(for F2).
3. Feed a 2500 Hz audio tone into MIC Input 4 (HIGH
LEVEL) and set level for a 3 VU gain reduction on
“AUDIO COMPR” meter. Set deviation pot R1 (F1) and
pot R2 for correct deviation specified by the FCC for the
assigned frequencies.
Encode switch should be off dur-
ing this adjustment . Refer to the SPECIFICATION
sheet (page 2) for designators.
4. Remove 2500 Hz tone. Place ENCODE switch in
“ON” position and adjust encode level pot R33 on
AUDIO BOARD, 800-166 for 1.0 KHz deviation.
AUDIO ADJUSTMENTS
1. With no audio input, switch METER to “AUDIO
COMPR” position and set “0 VU Adjust” pot R22 on
AUDIO BOARD, 800-166 to read 0 VU on the meter.
2. With ENCODE switch “OFF”, connect a harmonic
distortion analyzer to the audio output of the Marti re-
ceiver being used with the RPT-30. Feed a 100 microvolt
signal from the transmitter into the receiver RF input.
(from the sampling attenuator) NEVER FEED THE
OUTPUT OF THE RPT-30 DIRECTLY INTO A RE-
CEIVER! The input stage of the receiver will be de-
stroyed instantly! Modulate the transmitter with a 2500
Hz tone at 3 dB compression. Turn “Limit Level” pot
R26 on AUDIO BOARD, 800-166 to maximum counter-
clockwise position. Note distortion. It should be less than
2%. Slowly turn R26 clockwise until an additional 0.1%
distortion is indicated on the distortion meter.
3. With ENCODE switch “ON” and using a Marti re-
ceiver having a subaudible decoder which has been set to
27 Hz by an audio generator of at least 1% accuracy, ad-
just “Encode Frequency” pot R37 for maximum indica-
tion on the “DECODE SIGNAL LEVEL” meter of the
receiver.
4. Connect an audio voltmeter to the output terminals of
the Marti receiver. Feed a 100 microvolt signal into the
receiver from an RF attenuator/sampler connected to the
output of the transmitter.
Using an audio signal generator connected to MIC
Input 4 (HIGH LEVEL) of the transmitter with a level 20
dB below compression level at 2500 Hz, sweep the audio
over the audio response range for the transmitter model
number being aligned.
Refer to the
SPECIFICATIONS (page 2) for correct
response for designator on your transmitter.
At the maximum specified response frequency adjust
the tuning slug in coil L1 on AUDIO BOARD, 800-166
for maximum level or best response curve.
FREQUENCY MEASUREMENT
The RF output frequency of this transmitter should be
measured as often as necessary to insure on-frequency
operation and to comply with regulations. Frequency
measurement can be made at the FREQ. TEST jack (RCA
phono plug) protruding through the transmitter rear panel.
The adjustment procedure is covered in the section above,
MODULATOR ADJUSTMENTS.
PRE-AMP BOARD REMOVAL
To remove Pre-Amp Board, 800-251, from the chassis
follow the outlined procedure with care:
1. Remove knobs and hardware from four level control
pots on front panel.
2. Notice the Neutrik mic. connector has a small hole
near the center in addition to the three pin receptacles.
This hole contains a tiny locking mechanism. Using a
small (0.75” wide) flat blade screwdriver, insert tool into
hole and turn slowly until screwdriver engages connector
lock. Use care!
3. Turn screwdriver counter-clockwise (1/8 turn) until
mic. insert releases.
4. After following the above procedure on each input,
gently push the black plastic inserts out of the metal shells
while simultaneously pushing the gain adjust pots inward
until the board releases from the front panel.
Remove board from the chassis and service. To re-
install board reverse the above procedure. Be careful! The
locking mechanism is delicate.