Auxiliary Input And Output; Hints And Tips - Flightcom 403mc Installation & Operation Manual

IMPORTANT: The existing aircraft headphone and microphone jacks must be left in place and may be used as a convenient tie-in point to
connect wires 8, 17, and 21 to the radio. They will also serve as a standby radio connection in case the intercom is ever removed for servicing.
Wires 2, 7, and 9 must be connected to different (new) jacks.
Note: If your aircraft does not have a built-in Push-to-Talk switch, you will need to acquire a portable switch and plug it into another
microphone jack, installed in parallel with the pilot's microphone jack. You would not use the in-line jack on the PTT switch in this situation.
Optionally, you could use the same mic jack if the PTT switch were modified (see Fig. 9) to defeat the mic audio interrupt feature inherent
in most portable PTT switch models.
The copilot can transmit over the radio if pin 6 is connected to an existing copilot PTT switch and pins 16 & 17 are connected together.
Note: The DB25 connector shipped with the model 403mc intercom is pre-wired this way.

AUXILIARY INPUT AND OUTPUT:

(See Wiring Diagram) If a music source is not installed permanently in the aircraft (Auxiliary Input), a 3.5mm mini jack can be installed in a
convenient location to provide an interface for a portable recorder or CD player. The system output will be monophonic. Pin number 18 on the
wiring diagram is for auxiliary input, allowing you to listen to a tape player or other source. To record from the intercom system (Auxiliary
Output), install a second 3.5mm jack and connect it via one (1) 47k resistor to the pilot's headphone output, pin 9. DO NOT attempt to combine
both input and output functions on a single 3.5mm jack.
INTERCOM WIRING INSTRUCTIONS:
Use 20 or 22 gauge teflon-coated wire, (not provided). We suggest a 25 watt soldering iron. Route all wires away from aircraft controls. Make
sure that wires do not chafe on or come in contact with the control cables, push rods, trim actuators, chains, flap followers, etc. Avoid bundling
wires with RF coaxial cables, inverter, or synchro wiring. Use shielded wire on audio mic and headphone lines.
Make good solder connections and insulate connections with heat shrink tubing. Refer to the WIRE CONNECTION GUIDE and the CONNECTION
SCHEMATIC for connector pin numbers and connection information. The numbers on the diagram are on the solder terminal side of the connectors.
Connect the intercom power lead (pin 20) to a circuit breaker on the Avionics Power Bus. Do not connect to Flight Instrument Power. Avoid circuits
with motors, strobes, or other "noisy" devices. If you are not sure where to obtain power, consult with an avionics shop before proceeding.

HINTS AND TIPS:

If you have difficulty transmitting on the radio: Make sure the pilot's and copilot's microphones are not interchanged, and that the PTT lines
go to the correct switches. If this problem appears initially just after installation, check wires 2, 7, 8, and 17 for proper wiring. If you experience
a distorted sidetone while transmitting, it relates to improper shielding of the aircraft antenna cable. Usually, the tower receives you loud and
clear in spite of what it sounds like in the cockpit.
If you do not hear a sidetone while transmitting on the radio: If a sidetone is not heard, there are several possibilities: One, the radio
sidetone level may be adjusted too low or turned off. Two, perhaps the radio wasn't designed with a sidetone output, or it was not connected
during radio installation. Turn up the radio sidetone output if possible.
If the unit is completely dead: Make sure that the aircraft master switch is turned on. Check the power supply lead (pin 20) to make sure
there is voltage available between it and pin 1 (ground). Make sure the fuse or circuit breaker is intact. For an initial problem after installation,
verify that the wire number is correct. Check to see if the headphones are plugged in all the way. Verify that headset volume controls are turned
up. Are the headphone plugs corroded? Use steel wool or crocus paper to shine up the headset plugs. Be sure that the squelch is set properly,
as the intercom is quiet when muted.
If a high pitched whine varies with engine RPM: This is from an alternator or generator noise on the power bus of the aircraft. Check the
filter at the generator/alternator. Insulate all microphone jacks from the aircraft frame and run a separate ground wire to the intercom from each
jack. Be sure the ground lead from the intercom (pin 1) is connected to an avionics ground. In very bad cases, a commercial alternator noise filter
can help. Connect it in series with the intercom power lead. In severe cases there may be a blown diode in the alternator or a bad aircraft battery.
If the unit isn't loud enough or you lose parts of your sentences: Place the microphone as close to your lips as possible. IMPORTANT!
Make sure the squelch is not adjusted too high. While no one is talking, slowly rotate the squelch control just until the background noise disappears. Do not
turn the knob any further than necessary. Good headsets make a big difference here. You may find that one brand puts out a higher signal than
another. Attempt to equalize the sensitivity of all your headsets by adjusting the mic pre-amps (contained in the mic itself or in the ear cup).
If you are unable to squelch out all the background noise: Note that David Clark H10-30 headsets require that the mic preamp be turned
down all the way. This is accomplished be rotating the small nylon screw at the front of the mic fully counter-clockwise. Single earsets or other
tubular mic type headsets may not have the noise-canceling ability necessary for proper squelch operation. A full earmuff with a high-quality
noise-canceling electret or amplified microphone is the best way to go, although all aviation headsets will work to some degree.
If the background noise level is too high while speaking: The source is with the noise-canceling ability of the mic itself. Just one poor mic will
make the entire system noisy. Experiment with other headsets, using other planes and radios if necessary. Replace defective headsets with
good quality units, preferably with electret mics. Another approach is to turn down the volume control until the noise is at an acceptable level
and speak with more volume, the mic nearly touching your lips. This increases the signal to noise ratio by increasing the strength of your voice
against the apparent strength of the noise.
If it still doesn't work: Call or write with a detailed description of the problem. Most of the time an explanation will solve the situation. Don't
return the unit without contacting us first, since 98% of the time we are able to diagnose the problem via telephone, back to the installation, the
method of operation, the radio itself, or the headsets.
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