wiring second radio and noise

[flps_74]

Hello all,

Our aircraft (Ms 893E) is wired with one VHF comm (old Narco 11A - but
functionning with noise mind you). We decided to install a new comm
(found an Icom A200). The present setup is wired to a hard wired (no
jacks just wires) Telex intercom TC 200. We have two problems.
The first is the noise from the beacon-strobe in the audio system. I
will be working on solutions found on this group namelly ensuring that
the existing jacks connectors (both pilot and copilor are properly
grounded to intercom ground, not the aircraft frame. Further ensuring
that insulating washers are fitted to the jacks.

The second problem is that we do not have an audio selector panel
installation. Not being an avionic technician, I wish to know how to
connect the new radio parralel to the old. One would suppose that a
sort of "selector" switch for the microphone would be appropriate in
order to select on or the other tranceiver in order to transmit. The
"receiving" can be done simultanuously using volume control to
"prioritise".

Any comment or help woud be welcome

Marc Arsenault

[MikeMl]

flps_74 wrote:
> Hello all,
>
> Our aircraft (Ms 893E) is wired with one VHF comm (old Narco 11A - but
> functionning with noise mind you). We decided to install a new comm
> (found an Icom A200). The present setup is wired to a hard wired (no
> jacks just wires) Telex intercom TC 200. We have two problems.
> The first is the noise from the beacon-strobe in the audio system. I
> will be working on solutions found on this group namelly ensuring that
> the existing jacks connectors (both pilot and copilor are properly
> grounded to intercom ground, not the aircraft frame. Further ensuring
> that insulating washers are fitted to the jacks.
>
> The second problem is that we do not have an audio selector panel
> installation. Not being an avionic technician, I wish to know how to
> connect the new radio parralel to the old. One would suppose that a
> sort of "selector" switch for the microphone would be appropriate in
> order to select on or the other tranceiver in order to transmit. The
> "receiving" can be done simultanuously using volume control to
> "prioritise".
>
> Any comment or help woud be welcome
>
> Marc Arsenault

You need a double-pole double-throw miniature toggle switch to be used
as a "TRANSMIT SELECTOR". One pole switches the mic input from Com1 to
Com2 (comes from mic jack ring), while the other Pole switches the
Push-To-Talk (PTT or Key line) from Com1 to Com2 (comes from mic jack tip).

To sum the audio from the two receivers into the input of your TC200,
you can make a "poor man's summer" consisting of two 150 Ohm resistors
each wired between the respective "headphone audio output pin" of each
receiver to the common point which is wired into the "headphone audio
input pin" of the TC200.

What the hell is a Ms 893E?

[MikeMl]

flps_74 wrote:
> Hello all,
>
> Our aircraft (Ms 893E) is wired with one VHF comm (old Narco 11A - but
> functionning with noise mind you).

To get rid of the strobe noise, make sure that the TC200 and both COMs
are mounted very close to each other (< 10cm) and that the power/audio
grounds from these connect to one grounding screw to the airframe very
near the rear of the Com trays.

All distally mounted things like speakers, head-phone and mic jacks
should be locally isolated from the airframe, and separate ground wires
from these need to connect to the same grounding screw(s) as the Coms
and the TC200, thus defining a true "single-point-ground" for all audio
related devices. Remember that the COM trays force you put the
"single-point-ground" right on the tray mounting structure.

[flps_74]

Hello Mike,

Thank you. I will work on this Monday morning. I will let you know how
it went.

A MS 893E is a Morane Saunier Rallye (180 hp lycoming with a Hatrzell
constant speed prop). We use it for towing gliders during the summer
and flying around in the winter. Great stoll aircraft, slats and big
flaps. Very comfortable too. See the link below (hope it works).

http://www.sac.ca/index.php?set_albumName=New-Photos-From-Site-Authors&id=IMG_1754&option=com_gallery&Itemid=108&include=view_photo.php

Cheers

Marc