User Manual

DE
DANIELS
ELECTRONICS
4-2 VT-4R150 VHF Project 25 Digital Transmitter Instruction Manual
4.1.1 Repeater Interconnect Cable Pinout
The cable which is used to interconnect the receiver to a MT-4 Interim Transmitter connects
receiver audio and the ANALOG_COR* and DIGITAL_COR* signals to corresponding points in
the transmitter. The cable pinout is shown below. Signals shown in brackets are present on the
cable, but not used by either the receiver or transmitter for repeater operation.
Receiver End Pin No. Signal Name Transmitter End Pin No.
1 (not wired) 1
2 Audio 2
3 ANALOG_COR* 3
4 (LVDS +DATA) 4
5 (LVDS –DATA) 5
6 DIGITAL_COR* 6
7 (+8.8VDC for RPIM) 7
8 (not wired) 8
Shield (GND) Shield
4.2 Project 25 Compliant Repeater
The MT-4 Project 25 Interim Digital radios are currently offered in an interim version. Although
all the hardware required for fully compliant repeater operation is present in the receivers and
transmitters, a firmware upgrade will be required. It is expected that a new version of the Radio
Service Software will be released at the same time.
4.3 Repeater System Troubleshooting
Most problems in setting up a repeater are due to the way the transmitter uses bank A and B
channels to re-broadcast incoming signals in either analog or digital modes. It is important to note
that the receiver and transmitter have no connection between them apart from the demodulated
receiver audio, and analog and digital COR* signals. This can lead to confusion since the
transmitter doesn’t get any information from the receiver about which frequency or channel
number to key up on. The transmitter channel is determined by the state of the CSEL0-3 channel
select lines, and the receiver can only tell it to key on bank A (analog) or bank B (digital).
Q: Why does the transmitter’s Analog LED lighting when keyed on a channel programmed for
digital operation?
A: The transmitter has two LEDs labeled A and D, indicating that the transmitter is keyed in either
analog or digital mode. In the interim transmitter, these LEDs actually indicate that the transmitter
is keyed in Bank A (reserved for analog channels) or B (reserved for digital channels). Thus, if
Bank A channels are used for digital channels, the Analog LED will light when the transmitter is
keyed on a Bank A channel, even though the modulation is digital. This problem will be corrected
in the firmware upgrade to fully compliant Project 25 operation.
Q: Why is the radio not receiving / transmitting on the right frequency?
A: The M-3 motherboard has jumpers that allow one of 16 channels to be selected on a receiver or
transmitter. The factory default is to have them all set to ground the channel select lines CSEL0-3,
forcing the radio to operate on channel 1. On the receiver there is also a Bank A/B* line which
usually floats at +5V, selecting Bank A. There are jumpers inside the receiver and transmitter that
may have been removed to disable any or all of these lines. The receiver and transmitter have