PM501 Operation/Installation Manual Page 4 Revision 5, Jan 2003
priate points to the PM501. Finally, install a new
set of pilot headset jacks and hook directly to the
appropriate points to the PM501.
Electrical Noise Issues
Due to the variety of radio equipment found
in today's general aviation aircraft, there is the
potential for both radiated and conducted noise
interference. The PM501 has a power supply de-
signed to reduce conducted electrical noise on
the power bus by over 50 dB. Although this is a
large amount of attenuation, it may not eliminate
all noise when the amount of noise is excessive.
In addition, there must be at least 13.8 Volts DC
present at the PM501 for the power supply to
work in its designed regulation. Otherwise, it will
not be able to adequately attenuate all noise.
Shielding can prevent radiated noise (i.e.
beacon, electric gyros, switching power supplies)
however, installation combinations can occur
wherein minor interference is possible. The
PM501 was designed in a RFI hardened chassis
and has internal bypass capacitors on all input
lines. RFI can still cause problems, like low or
distorted sidetone, if correct shielding techniques
are not observed.
Ground loop noise occurs when there are
two ground paths for the same signal, i.e. air-
frame and ground return wire. Large cyclic loads
such as strobes, inverters, etc., can inject audible
signals.
Follow the wiring diagram very care-
fully
to help prevent ground loop potential. Radi-
ated signals are also a factor when low level mic
signals are "bundled" with current carrying power
wires. Keep these cables separated as much as
possible.
Mil-spec 2– and 3-conductor shielded wire
MUST be used as shown in the installation dia-
gram for proper operation. Use of other types
could void the warranty.
It is crucial that you use insulating washers
on all microphone and headphone jacks to iso-
late the audio signal ground from the aircraft
ground.
Power Requirements
The PM501 is designed to work with either
12 or 28 volt DC negative ground systems. The
PM501 must be externally fused with a 1 am-
pere circuit breaker.
Side Tone
If the aircraft radio does not have sidetone
(the ability to hear your voice during radio
transmissions) the PM501 can be modified to
provide sidetone for you. Call the factory for
details.
Entertainment Hook Up
A low cost entertainment device (CD
player, cassette player, etc.) can be connected to
the PM501. You may want to install a
⅛
" con-
nector (not provided) somewhere in the panel so
that you can easily connect an entertainment
device.
The entertainment will be automatically
muted when the ICS becomes active. The “Soft
Mute™” feature slowly returns the music to full
NOTE
: Auxiliary microphone and headset
jacks are
required
for a complete installation.
These provide troubleshooting and a back-up
access to the aircraft radios.
Note
: Use the low level (or line) output
from any music device to connect to the
PM501. Maximum input level is 2 V peak-to-
peak.
DO NOT USE SPEAKER OUTPUT.
Revision 5 Feb 2003 Page 5 200-118-0005
volume when the ICS is quiet. NOTE: Aircraft
radio reception DOES NOT mute the entertain-
ment.
External Push to Talk Installation
Part of the installation includes the installa-
tion of PTT (Push To Talk) switches that allow
the use of your aircraft communications radio for
transmissions.
There are three configurations that can be
used. You select the case that best fits your instal-
lation requirements.
NOTE: Only the person who presses their
PTT switch will be heard over the radio.
CASE I
PTT built into the pilot and copilot
yokes
Simply install the plugs from the head-
set into the aircraft headphone jacks. Use
the yoke mounted PTT to transmit. No
other action is required.
CASE II
Built-in PTT on the pilot side only, but
copilot transmit capabilities desired.
This configuration requires a
modified
external PTT plugged into the copilot's
mic jack. See Appendix A for modifica-
tion details. When the copilot's PTT is de-
pressed, this activates an intercom relay
that switches the mic audio input to air-
craft radio to the copilot.
CASE III
No built-in PTT switch at all
If there is no built-in PTT switch at all,
an external, properly modified PTT
switch is required. Both the pilot and
copilot may use an external PTT. (See
Appendix A.)
OPERATING INSTRUCTIONS
With the installation complete, turn the
PM501 on pressing the volume control knob
(left knob). This also engages the automatic fail-
safe system.
Adjusting The Volume
The volume control knob adjusts the loud-
ness of the intercom and music for all headsets.
Turning the control clockwise increases the
audio. Many headsets have volume controls on
them. If it becomes necessary to reduce the vol-
ume for an individual passenger, the three oth-
ers should be set at maximum, and the unit vol-
ume set for a comfortable level. The individual
can then reduce their volume accordingly.
The volume control on the PM501 affects
the volume level of the aircraft radio for the co-
pilot and passenger . The radio volume is not
affected for the pilot. This gives added flexibil-
ity for communications requirements. Note:
PM501 Front Panel Controls
Volume
Control
CW to
Increase
VOX Squelch
Control CW to
increase amount of
voice necessary to
open
Mode
Switch