Motorola CDM1250, Basic Service Manual

Page: 51 / 92

Radio Programming and Tuning Procedures 4-9
4.4.7 VCO Attenuation
Table 4-6: Deviation Specifications for UHF/VHF/LowBand Radios *
*These values are up-to-date as of the print date. For the latest values and procedures, refer to the
Tuner online help.
4.4.8 VCO Attenuation (25 kHz)
Perform the 25 kHz VCO attenuation procedure as follows:
1. Under the Tx Align menu, select VCO Attn. 25 kHz .
2. Begin with the lowest frequency. Select the thumb of the slider at the lowest frequency point,
then press the
PTT Toggle button to key up the radio at the corresponding frequency point. The
spin control can also be toggled via its up/down arrow buttons. The softpot value can also be
typed into the edit control. Press
ENTER to confirm the selection.
3. Inject 1 kHz at 800mVrms to the external microphone audio path.
Note: 1. Tuning of the modulation balance must be accomplished first. The transmit devi-
ation Limit softpot sets the maximum deviation of the carrier. Tuning is performed
for 12.5 kHz, 20 kHz, and 25 kHz channel spacing. Tuning for 25 kHz channel must
be done first for all frequency points. Tuning for 12.5 and 20 kHz channel spacing
determines only the offset to the previously tuned deviation for 25 kHz tuning
channel spacing. For 12.5, 20 kHz channel spacing, only F7 is used for tuning.
The 30 kHz channel spacing which uses 5.0 kHz maximum system deviation are
covered by the 25 kHz tuning.
2. When using test box RLN4460, set the METER OUT toggle switch to the “MIC
PORT” position and METER OUT selector switch to “MIC”. Inject 1 kHz tone, and
800mVrms to AUDIO IN. The 800mVrms should be measured at the AC/DC
METER.
3. Depending on the radio model and the customer settings, the signal injected in
accessory connector Pin 5 or the signal from an option board may be transmitted
simultaneously with other signals, for example from the microphone or internally
generated signaling. In this case the peak signal level is the sum of the individual
signal's peak levels and can exceed the maximum allowed transmit deviation
level. To prevent over deviation, the maximum deviation must be measured with
both signals present and if the deviation still exceeds the range defined in Table
4-6, the VCO Attenuation must be re-tuned, so that the deviation stays in the tun-
ing range with both signals present.
4. Tuning of the modulation balance attenuation must be performed first.
Band Channel Spacing
Rated System
Deviation
Deviation (kHz)
UHF/VHF/LowBand 25 kHz 5 kHz 4.4 – 4.6
LowBand (20 kHz sys-
tems in North America) 20 kHz 5 kHz 4.4 – 4.6
UHF/VHF 20 kHz 4 kHz 3.4 – 3.6
UHF/VHF/LowBand 12.5 kHz 2.5 kHz 2.2 – 2.3