Technical Manual Technical Description
© SPECTRA ENGINEERING 2006 Revision 4.2.3
51
3.17.2 2Wire or 4Wire Selection, Balanced VF
3.17.2.1 Description
Option T19 and T26 both provide the user to be able to select between 2 wire
or 4 wire systems, they also both have balanced and isolated VF I/O as well
as isolated E (PTT) and M (Mute) leads. The T19 has dual E&M leads, this
provide a Qualified and Non-qualified M leads as well as E leads with
subtones and with out subtones. The second E&M connection points are
found on CN3 DB25 connector.
The E lead is opto isolated and may be asserted by applying a DC voltage
between 5V and 48V with any polarity between CN9 Pins 7&8 (JMP4 &
JMP5 removed).
Provision is also made to internally source or Earth (JMP4 and JMP5) so that
the activation can be done Via CN9 Pin8 (+12V DC) or (GND), in which
case the E lead is asserted by grounding or pulled up to 5V (depend on JMP4
& JMP5 settings) on CN9 Pin8
The M lead is relay isolated and the common and normally open contacts are
brought out via CN9 Pins 5&6. The relay contacts are rated at 500mA.
Note# In REV C PCB for 2 wire mode, to have the correct matching for 600R
please fit a 560R resistor is in parallel to R77(above IC4) and across R130 &
R129 (Right hand side of PCB above RV4)
3.17.3 VF Delay
3.17.3.1 Description
This option provides a 40mS delay to the received audio. When the option is
fitted delayed audio is fed to the line and talk through paths but discriminator
audio (output on CN1 Pin4) is undelayed.
This option is intended for two main applications. Firstly when the delay is
fitted the mute "crash" characteristically heard when a mobile releases its
PTT but the repeater tail continues, it is eliminated. Secondly systems
(including trunking systems) which have mixed voice and data on a channel
can delay the VF signal to line and air so that in the event that a data stream is
detected (by the data controller) the VF to line and air can be disconnected
for the duration of the data burst thus avoiding radio system user annoyance.
Internal switches in the MX800 may be used to disconnect the audio under
the control of the RX TALK line (CN1 Pin7) the sense of which may be
inverted using JMP12 on the micro controller.
This option may be fitted at order placement or retro fitted subsequently. The
Option PCB assembly is fitted above the Micro controller on four hex pillars.
A 16-way ribbon connection is made from the Option PCB to SKK on the
micro controller card. The links on the Option card are set as below. Once the
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