SYSTEM OPERATION
Once the radios are selected, pilot or observer can
transmit at any time simply by pressing their PTT
switch. When one position transmits, several things
take place automatically to the transmitting side of
the SPCC:
• The intercom between the two positions is turned
o.
• The receive audio of the radios not selected by the
XMIT SELECT switch are muted, regardless of the
position of the receive select switches.
• The selected radio is put into transmit mode.
• The headset microphone audio (your voice) is sent
to the selected transmitter.
• Sidetone is generated and sent to your headphones.*
* Sidetone is a portion of the transmitted voice signal
sent back into your headset, so that you can hear what
you are saying while transmitting. The RECeive VOL-
ume control adjusts the volume level of the sidetone
that you hear in your headset.
The non-transmitting side is not aected (except for
intercom) when the other side transmits. The non-
transmitting side can monitor the transmissions of
the other side by simply selecting the same radio on
his side of the SPCC. Of course, when the PTT switch
is released, (stop transmitting) all functions return to
normal, instantly and automatically.
Simultaneous Transmit is the most attractive and
powerful feature of the SPCC. Both pilot and ob-
server can transmit at the same time - either on
separate radios or on the same radio transmitter!
When on dierent radios, the pilot and observer
will not interfere with each other’s communications.
For example, the pilot can talk to air trac control
while the observer talks on one of the FM radios to
the ground crew, or vice versa. On the other hand,
they can also transmit on the same radio transmitter.
If, for example, the observer is talking on one of the
radios, the pilot can jump right in and add to the con-
versation simply by pressing his PTT switch. Both voices
will be heard by the receiving station.
TRANSMIT MICROPHONE GAIN ADJUSTMENTS
Transmit microphone gain adjustments for both FM
and the aircraft radios are provided through three small
holes on the top of the SPCC unit. These adjustments
set the microphone audio level going to the radios dur-
ing transmit. Adjustment should be made only if the
outgoing radio transmissions are reported as weak or
garbled. The Aircraft Radio Mic Gain Adjustment is set
at the factory for standard aircraft radios and should
not need any adjustment. The two FM Radio Mic Gain
Adjustments, however, will more than likely need to be
initially set to your particular FM radios. These levels,
once set, should never need adjustment again unless,
of course, the type of FM radios used are changed.
The following simple procedures take you through
the adjustment of the FM and A/C mic gain levels. If
desired, a qualied radio technician can do this for you.
FM-1 & FM-2 Radio Mic Gain Adjustment can be made
through the middle and right hole respectively, just to
the right of the FM-1 radio interface connector with a
small, at bladed screwdriver. The basic adjustment
concept for both FM radios is simple. On a one at a
time basis, you will be setting the level and clarity of
outgoing transmissions of the FM radios, when they
are hooked up through the SPCC, to match or exceed
that of transmissions on the radios when they are not
connected to the SPCC. To do this, you will need to
transmit and receive on the FM radios to a remote
station. Arrange to have someone nearby with radios
compatible to the FM radios you are using with the
SPCC. Then rst for FM-1…
1. Set the ON/BYPASS switch to the “BYPASS” position
and connect the SPCC up to power, as normal. Plug
in the observer’s PTT switch and headset. (It is not
necessary to connect the A/C radios or the pilot’s
headset or PTT switch for this adjustment.) Do not
connect the FM-1 radio to the SPCC at this time. Set
the observer’s XMIT SELECT switch to “FM-1”, and
all three receive select switches to “OFF”.
2. Set the SPCC aside for a moment. With the FM-1 ra-
dio disconnected from the SPCC, transmit as normal,
on the FM-1 radio, to the remote station. Transmit
long enough so that the receiving station can get
“calibrated” to your transmission (voice) level.
3. Connect the FM-1 radio to the SPCC as normal with
the FM-1 interface cable. Put on the observer’s head-
set and turn the SPCC “ON”. Verify FM-1 radio recep-
tion. If OK, use observer’s PTT to transmit to your
receiving party. If receiving station reports weak
transmission, use the screwdriver to turn the FM-1
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