User's Manual

DANIELS
ELECTRONICS LTD.
TM
25W AM Power Amplifier Instruction Manual IM71-AMP3A130-25 4-3
4.2 RF Amplifier Board Alignment
Refer to Figure 1 for location of adjustment capacitors.
This procedure assumes the use of 2 separate subracks with the exciter transmitter in system A and
the 25W power amplifier in system B.
1. Remove the top extrusion cover housing from the exciter, set the exciter frequency at
128MHz (channel number 1200) and install the exciter in the system A of the M-2
or M-3 subrack. Remove all receivers from the subrack assembly (this will facilitate
calibration access).
2. Install the extender card in the designated location for the AMP3A130-25 Power
Amplifier (System B). Connect the RF output of the exciter to the input of the
power amplifier module and the output to a Communications Service Monitor.
3. Apply +13.8Vdc to the subrack system A and +28Vdc to the subrack system B,
activate the exciter transmitter and the power amplifier.
4. Turn the power adjustment potentiometer R19 in the exciter to achieve approximate
25W RF output. R19 is labeled "RF Level" and is accessed through the bottom of
the exciter transmitter amplifier case.
5. Monitor the RF power output and adjust C2, C3 and C10 on the RF power amplifier
board for maximum output power and minimum current. Check that the RF output
power is within 25W±1dBc (app. 20%) when the exciter frequency is set to 118,
128 and 138MHz (channel number 0000, 1200 and 2400). Note that C2 and C3 are
more effective in adjusting the output "flatness" over frequency.
6. Apply 1k/-25dBm AF signal into the balanced input of the exciter and adjust the
potentiometer R35 in the exciter to get 30% modulation. R35 is accessed through
the bottom of the exciter transmitter amplifier case, labeled Audio Level. Increase
the audio signal level to –8dBm, the modulation level should be 90±5% and the
audio distortion should be below 10%. Adjust C10 on the RF power amplifier
board for minimum audio distortion and maximum RF output power.
7. Confirm that the audio distortion is below 10% at 90% modulation and the RF
output power is within 25W±1dB at 0% modulation when the exciter frequency is
set to 118, 128 and 138MHz, respectively. Go back to step 4 if these specifications
are not met.