Daniels VT-3/140-SWA2, Instruction Manual

Page: 93 / 262

Audio Processor Board Instruction Manual 1-5
1.5 Turn-on Time
This measurement is made with the standard factory settings with a 1 kHz tone applied to the
balanced input. The turn-on time is the time it takes the FM Audio Processor to output a stable
audio signal to P3-1 from the time its power (+8.0 VDC) is switched on.
The turn-on time can be virtually eliminated by configuring the FM Audio Processor for
continuous audio standby (see section 1.7 Transmitter Standby Modes). The drawback is that
more current is used to enable the audio circuits to minimize the turn on time. The bulk of the delay
is in the powering of the compression amplifier. For applications that do not use the compression
amplifier, the fast turn on times apply as in the case of data transmission, or audio with no
compression.
Table 3 Turn On Time
Mode Turn on time Audio Processor
Standby Current
Fast turn on – higher current Approx 1mS 15 mA
Current save – slower response Approx 150mS 450uA
1.6 Low Frequency Modulation
The transmitter has an additional option to address low frequency user modulation requirements. A
phase modulated bandwidth from 0 (dc) to 100 Hz (PLL loop filter bandwidth) allows specialized
applications such as paging or trunking where a separate low frequency digital/analog modulation
channel is required. Low Frequency Modulation allows external access to the low frequency
modulation capabilities of the synthesizer module. The DIRECT MODULATION inputs on the J1
control connector of the M-3 motherboard will be used (B20 for TX A, and A20 for
TX B). Refer to “Data Modulation and Signalling Applications Manual”, P/N AM20-DMS for
specific FM Audio Processor configuration methods.
1.7 Transmitter Standby Modes
The MT-3 series transmitters has 8 different standby modes that trade-off standby current
consumption for start-up speed.
Three of these jumpers are on the Transmitter Main Board :
•
J6 which always turns on the '+9.5 VDC Switched' supply,
•
J7 which selects the power source for the MT-3 FM Audio Processor
•
J18 which selects the enable line for the OS-3 or OS-3H Synthesizer, or OC-3 Crystal
Controlled Oscillator module.
Additionally, there is a jumper on the FM Audio Processor Board:
•
JU36 which determines the power hookup for the dual compression amplifiers