Transmitter Alignment
32
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
frequency response test
Measurements are made at JU8 with respect to ground.
1.
Reduce Audio Generator level to –18 dBm (98 mV RMS).
2.
Step frequency to 300, 500, 1000, 2000 and 2500 Hz.
3.
Ensure that the results conform to the 6 dB//- 1 dB from 500 Hz to 2500 Hz
referenced to 1000 Hz (+1/-2 dB at 300 Hz).
Subtone Input test
1.
Change Audio Generator frequency to 100 Hz and maintain level at –18 dBm (98 mV RMS).
2.
Connect signal to Subtone Input 1 (P2-2) and ground (P1-4).
3.
Refer to the Waveform Levels Table above and confirm levels.
temPerature ComPenSatIon
The FM Audio Processor includes temperature compensation circuitry to maintain a constant
transmitter audio deviation with a fixed level input signal. It is capable of not only compensating for
temperature related level variations within the audio processor (typically –0.3 to –0.5 dB at –40ºC),
but can also compensate for changes caused by the synthesizer that is not equipped with its own
temperature compensation.
Specifications:
When a 1.8 kHz tone is applied at a level of +10 dBm to the balanced input of the transmitter, the
transmitter deviation shall be ±4.4 kHz at room temperature and can vary from ±4.4 kHz to ±5.0 kHz
from -40ºC to +60ºC.
Since the specifications of the components used in the synthesizer or oscillator may change over
time, changes to the temperature compensation circuit may be necessary even for the same type of
equipment.
Contact the factory for more information on values used.
fm audIo ProCeSSor JumPer ConfIGuratIonS
For Default / CTCSS / LTR® / DCS configurations, see Table 3.
