NOTE:  All descriptions/direction relate to the XTR role.

The board is designed to plug directly into the 34-way connector on the trunk-mount XTR in place of the normal ribbon cable and control head.  Input from and output to the external equipment is via a nine-pin sub-D connector.
(see table below for pinout).

KEY FEATURES OF THE CURRENT PROTOTYPE DESIGN:

1.    Audio out - 3 ports:

A.    Full speaker (bridge) output to 2-pin header - volume determined by VOL trimpot.
B.    Audio to DE9-5 is taken from one speaker leg (see A above), via blocking capacitor and a series resistor.
C.    "Local speaker" - from other speaker leg (see A above), via blocking C and series R to "fader" pot and then to 2-pin header (Note 1).

2.    Audio in - two ports:

A.    4-pin header for standard Midland preamplified mic (ST1/XTR type).
B.    DE9 to a mic preamp circuit, with transformer isolation.  This requires only dynamic mic level in from the external equipment.
        (Selection of A or B to feed the XTR is via a jumper on a 3-pin header.)

3.    Decode/busy out.

A.    Audio mute action (i.e. busy, plus decode where programmed) buffered and driving relay output to DE9.
        Output function is jumper selected.  On XTR Rx activity, this line can:

• pull down to 0V; or
• pull up to +5V; or
• pull up to +13V.

B.    Standard XTR busy LED plus a "decode" LED (Note 3).

4.    PTT in.

Unbuffered.  Pull down to ground = PTT as per standard XTR.  Diode clamped to +5V rail to limit positive excursion.

Tx LED (bi-colour Red/Green as per Midland practice).

OTHER  FEATURES

1.    ON/OFF toggle switch (Note 1)
2.    LEDs for PWR, TX/ BUSY, DECODE
3.    Header for MON switch (2 pin)
4.    Header for UP/DN switch (3 pin)
5.    Header for channel display (7 pin)

Note 1:  Optional fitment.

Note 2:  Scan buttons/LEDs are not supported.  This unit is intended for basic operation in packet service or for link or remote base roles.

Note 3:  When no CTCSS is programmed, the output keying signal follows carrier squelch action (i.e. the Busy LED).  When CTCSS is programmed, keying signal requires decode plus busy.  This mimics the receiver audio activity.

Board size:  3000 * 2050 The standard version is designed to plug directly into the XTR chassis via the ribbon cable receptacle.  Where connection to the XTR chassis is required to be achieved using ribbon cable, an alternate version (size 3000 * 2200) is available.  The D-Sub connector, the ON/OFF switch and all the LEDs have been aligned to permit mounting the board behind a panel or inside a box/case. Corner mounting holes have been provided on both boards.