Specifications

LBI-33057
21
SET-UP PROCEDURE
1. Program the radio with the low, middle and high-
side re tune channels in the desired operating fre-
quency band. The low and high-side channels
should be 20 MHz apart and the middle channel
should be centered between the two. Do not ex-
ceed the frequency range limits for the RF Board.
2. Separate the Front and Rear Cover Assemblies
and connect the RF/Logic Extender cable be-
tween the RF Board and the Control Board.
SYNTHESIZER RETUNING
1. Set the radio to the middle retune channel.
Monitor the VCO tuning voltage at TP1 (A5 pin
3) with a dc voltmeter. Adjust the RX VCO coil
should be for a reading of 2.5 Vdc. See Figure 10.
2. Set the radio to the lowest retune channel. The
monitored voltage greater than 1.0 Vdc.
3. Set the radio to the highest retuned channel. The
monitored voltage should be less than 4.0 Vdc.
4. If the lowest and highest retune channels push
the VCO tuning voltage measured at TP1 outside
of the specified limits, slightly readjust the RX
VCO coil to center the low and high retuned
channel tuning voltages within or around this 1.0
- 4.0 Vdc window.
5. Repeat steps 1 - 4 for the TX VCO coil with the
following exceptions: The radio must be keyed
when adjustments are made to the TX VCO coil.
Also, connect an appropriate RF load to the an-
tenna before keying.
6. Turn the radio off and connect the PC Program-
mer to the radio. Power the radio back up. Using
the PC Programmer, set the modulation Tracking
Data value to OD (hex).
7. Set the radio to the middle, retune channel. 8.
Couple a modulation analyzer (with a monitor-
ing oscilloscope) to the RF output of the radio.
Set the modulation analyzer's filters as follows:
no high-pass filters and 20 kHz low-pass filter.
The modulation analyzer should have an almost
dc response. If it does not, an alternative is to use
a second M-PA monitoring the transmit fre-
quency and monitor the discriminator output
from the RF Board with a dc coupled oscillo-
scope. The monitoring point is J101 pin 4.
9. Apply a 110 mV rms, 1 kHz tone to the TQ-
3370's modulation input. Key the radio from the
TQ-3370 and adjust R19 on the RF Board for a
deviation of 2.5 kHz.
10. Modify the RF/Logic Extender cable so a low-
frequency signal can be injected directly into the
RF Board. This modification procedure is out-
lined in the TRANSMITTER ALIGNMENT sec-
tion of this manual.
11. Using a 100 µF (or greater) capacitor, couple 20
Hz, 1.0 Vpp square wave signal into TX MOD
(J102 pin 1).
12. Key the radio and monitor the demodulated out-
put from the modulation analyzer. Adjust R18
(modulation balance pot) for a good square wave
response as shown in Figure 11.
Figure 11 - Typical TX Modulation Low-Frequency
Response Curves
RECEIVER RETUNING
Retuning the UHF M-PA receiver involves retuning
the two (2) helical filters at the input and output of RF
Amplifier module A6. There are three (3) different pro-
cedures that can be used to retune the receiver. The most
accurate method involves the use of a network analyzer.
If a network analyzer is not available, a spectrum ana-
lyzer and signal generator can be used, but with less ac-
curate results. Finally, the receiver can be re tuned with
some compromise in receiver performance using a best
quieting (SINAD) tuning technique.