Motorola Two Way Portable Radio Ht1000 Jt1000 Mt2000 Mts2000 Mtx Series 6881200c75 B Manual

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Each SERVICE screen provides the capability to increase or decrease 
the ‘softpot’ value with the keyboard UP/DOWN arrow keys 
respectively. A graphical scale is displayed indicating the minimum, 
maximum, and proposed value of the softpot, as shown in Figure 3.
Adjusting the softpot value sends information to the radio to increase 
(or decrease) a DC voltage in the corresponding circuit. For example, 
pressing the UP arrow key at the Reference Oscillator screen instructs 
the radio microprocessor to...

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Front-End
Pre-Selector
(VHF/UHF only)NOTE:This procedure is only required for tuning the 
front-end filter varactors in the VHF and UHF 
models. The 800 and 900 MHz models utilize a 
stripline pre-selector. 
1. Set the Test Box (RTX4005B) meter selection switch to the “VOL” 
position, and connect a dc voltmeter capable of 1mV resolution 
on a 2V scale to the Test Box AC/DC meter port to monitor the 
Received Signal Strength Indicator (RSSI).
2. From the SERVICE menu, press F3 to select RECEIVER...

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8. Select the Hear Clear RATED AUDIO softpot, and adjust the UP/
DOWN arrow keys to obtain rated audio (3.74 Vrms) into a speaker 
(28 ohms) or equivalent resistive load.
9. Press F8 to program the softpot value. 
10.Press F10 to return to the RECEIVER menu.
SquelchNOTE:Verify that audio output is set to rated audio 
(3.74 Vrms)
1. Select the 25kHZ squelch tuning menu. (note: 25 kHZ must be 
tuned before tuning either 12.5kHZ or 20kHZ squelch).
2. With no signal applied, decrease the softpot value...

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Tr a n s m i t
Deviation Balance 
(Compensation)Compensation alignment balances the modulation sensitivity of the 
VCO and reference modulation (synthesizer low frequency port) lines. 
The compensation algorithm is critical to the operation of signalling 
schemes that have very low frequency components (e.g. DPL) and 
could result in distorted waveforms if improperly adjusted. 
NOTE:Disable all audio band filters on the service monitor.
NOTE:(Secure-Equipped Radios Only)
If a secure module is...

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9. Repeat steps 3 through 8 for the remaining test frequencies.
10.Press F10 to return to the TRANSMIT menu.
NOTE:The step size change for step 5 is 
approximately 2.5% per softpot value. This 
adjustment should only be made to the 3kHz 
deviation. Do not adjust the 80Hz deviation.
Transmit Deviation 
Limit1. Press F5 to select the TRANSMIT DEVIATION LIMIT softpot. The 
screen will indicate the transmit test frequencies to be used.
2. Begin with the lowest test frequency shown on the screen.
3. With...

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4. Press F6 to dekey the radio, and press F8 to program the softpot 
value.
5. Press F10 to return to the TRANSMIT menu.
VCO Crossover 
FrequencyNOTE:This procedure is only required after the field 
repair of a VHF or UHF VCO. 
In order for a phase-locked-loop to tune very wide bandwidths, both 
negative and positive control voltages (Vcntl) are required. This 
procedure sets the crossover frequency at which the negative Vcntl 
(or –Vee) switches from zero to negative.
Transceiver Board...

25 VCO varactors (CR201, 202, and 203) in “C” and later kits are not 
interchangeable with VCO varactors in earlier kits; Motorola parts and 
part numbers are different. When replacing a VCO varactor, Identify 
the transceiver board and order replacement parts from the applicable 
parts list.
UHF, 403-470MHz RadiosUHF transceiver board (403 - 470MHz band split) NUE7231 and 
NUE7240 (“C” and later) kits include new VCO varactors, and are 
factory aligned with a new transmit VCO crossover frequency of...

26Since the transmit crossover frequency has changed, whenever 
transmit VCO crossover alignment (an RSS function) is performed, 
UHF band split and circuit board identification will be important. 
UHF band split can positively be determined by the markings on 
the power amplifier shield. If the power amplifier shield marking 
is 25U04 or 85Y10, then the transceiver is a 403 - 470MHz band 
split. If the power amplifier shield marking is 25U05 or 85Y11, 
then the transceiver is a 450 - 520MHz band split....

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RX VCO Crossover
Procedure1. From the SERVICE menu, press F3 to select RECEIVER alignment.
2. Press F5 to select the RECEIVE VCO CROSSOVER softpot. The 
screen will indicate the receive test frequency to be used.
3. Connect a dc voltmeter capable of 1mVolt resolution to test point 
5 (TP5), which is accessible through a hole in the bottom side VCO 
circuitry shield.
4. Beginning with the default softpot frequency of line 2, adjust the 
UP/DOWN arrow keys until the voltage reading at TP5 is
3.0...

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6. Press F6 again to dekey the radio.
7. Press F8 to program the softpot value; press F10 to return to the 
SIGNALLING menu.
MDC 1200 1. From the SERVICE menu, press F4 to select SIGNALLING 
alignment.
2. Press F4 to select the MDC softpot.
3. Press F6 to key the radio on the test frequency. The screen will 
indicate that the radio is transmitting.
4. Measure the MDC deviation on your service monitor.
5. Use the UP/DOWN arrow keys to adjust the MDC deviation per 
Table 18.
6. Press F6 again to dekey...