AC-701 TELEPHONE AND 2-WIRE INTERFACE 1-3
3. While listening on the headset, push the A balance momentary switch and
adjust the A balance trimpot for minimum tone in the headset. Repeat this
procedure with the B balance switch and trimpot. If the unit starts to
oscillate or motor-boat, back off both gain controls slightly and re-balance.
4. Disconnect the test headset.
3-/4-WIRE MODE BALANCING: The procedure is the same as for the 2-wire
mode, except the B balance is inoperative.
ADDITIONAL NOTES
1. The test tone levels heard in the system are affected by the Transmit and
Receive gain control settings.
2. Attempting to get too much gain from either system can cause instability and
oscillation.
3. If you are interfacing to a TELCO line and cannot obtain a satisfactory null
on the B balance, the value of capacitor C39 should be increased. Your
authorized Clear-Com dealer can try adding from .05 uF to .1 uF across the
existing cap.
PHONE HOLD
The AC-701 can interface Clear-Com with standard telephone systems.
The AC-701 is intended for use on closed/PBX type telephone exchanges.
The user may dial an outgoing call from a telephone extension, switch the
AC-701 to “Phone Hold”, and then hang up the receiver to keep the party
on-line for intercom purposes.
Likewise, an incoming call may be answered by the AC-701 that’s in the “Hold”
condition (instead of lifting the telephone receiver off the hook). When the
phone rings, set the ‘Phone Hold’ switch (on AC-701 front panel) to the “Phone
Hold” position. The AC-701 effectively answers the phone, connecting the caller
to the intercom system. The red LED adjacent to the switch glows to indicate
that the telephone line is seized.
The AC-701 provides a simulated termination to maintain its stability. This
termination is automatically applied when the DC voltage on the TELCO line
input is removed.
For proper operation, the holding coil circuit should be used only on a standard
TELCO line “wet” pair, i.e. a telephone line with a DC voltage across it. For
interfaces with non-TELCO “dry” two wire lines, the holding coil is not needed
and the internal switch on the holding coil module should be set to “bypass”.
Warning: To prevent damage to the Holding Coil Circuitry; when the AC-701 is
used as an interface to TW (RTS type) systems, the internal slide switch
(S1 on the PCB) MUST be set to “BYPASS”.
