Ptt And Dc Remote Control; Microprocessor Controller - RF Technology Eclipse Series Operation And Maintenance Manual

5.10 PTT and DC Remote Control

5 CIRCUIT DESCRIPTION
The composite audio from U7a is fed through the 3Khz low pass filter U7b. When the links
on JP23 are in their default state, the filtered audio is coupled to the TCXO voltage tuning
input and the modulation balance trimmer RV2. RV2, R99 and R98 attenuate the modulation
signal before applying it to the VCO via varactor D3.
When DMTX board option is required, Jumper JP23 allows the audio paths to be re-routed.
The DMTX board provides for an external digital modulation input signal. When the two
links on JP23 are positioned in the middle of the 6 pin header, the audio from the exciter is
passed to the DMTX board via pin 5 of JP15, where the signal is conditioned and then
returned from the DMTX board via pin 2 of JP15, and passed to the two modulation points.
RV2 adjusts level of the audio used to modulate the VCO. This primarily effects the deviation
of audio frequencies above 500 Hz. RV2 is used to balance the high and low frequency
deviation to obtain a flat frequency response relative to the desired characteristic.
5.10 PTT and DC Remote Contr ol
Two main PTT inputs are provided. The first, a direct logic level input, is connected to pin 3
of the system connector. The transmitter can be keyed by applying a logic low or ground on
pin 3. Pin 3 connects to the PTT logic and microprocessor through D10.
DC current loop control can be used for remote PTT operation. The current loop can be
configured by JP9, JP10 and JP11 for use with either a remote free switch or a remote
switched source.
Opto-isolator ISO1 is used to isolate the loop current signal from the transmitter PTT logic.
The loop current passes through the input of ISO1 and the output of ISO1 connects to the PTT
logic.
A bridge consisting of diodes D6, D8, D9 and D14 ensures correct operation regardless of the
current polarity. Q17 limits the current and D7 limits the voltage input of ISO1. Any low
voltage current source capable of providing 2mA at 4V or switching circuit with less than
4.8k¿ loop resistance can be used to switch the DC loop.
The test PTT button on the front panel and the local microphone PTT button will also key the
transmitter. Both of these also mute the line audio input. The microphone line also enables
that audio input.
A DMTX board can also cause the exciter to key up. When TX (or TTL_TX) signal is
received by the DMTX board, it pulls pin 6 of JP15 low, which in turn asserts the
PTT_WIRE-OR signal, causing the microprocessor (U13) to key the exciter up.
5.11 Micr opr ocessor Contr oller
The microprocessor controller circuit uses a single-chip eight bit processor and several
support chips. The processor U13 includes non-volatile EE memory for channel frequencies,
tones, and other information. It also has an asynchronous serial port, a synchronous serial
port and an eight bit analogue to digital converter.
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RF Technology T800 Page 16