Sigtronics SPCC-2 - Manual (Page 5)

iii. “BOTH” position permits you to hear both
the aircraft radio(s) and the FM radio at the
same time.
4. The AUXliary audio source is selected by the AUX/
OFF switch. In the “AUX” position, you can hear it,
and in the “OFF” position you cannot.
5. Receive Volume Controls (REC VOL) are general
volume controls, meant to provide overall
listening level for all three radios simultaneously
- A/C, FM, and AUX. Finite volume adjustments of
any individual radio should be done by altering
the radio volume control at the radio itself.
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
off.
• The Auxiliary audio, if selected, is muted.
• The receive audio of the radio not selected by the
XMIT SELECT switch is muted, regardless of the
position of the AUTO/OFF/BOTH switch.
• 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 VOLume control adjusts the volume level
of the sidetone that you hear in your headset. If the
AUTO/OFF/BOTH switch is in the “OFF” position
however, you will not hear this sidetone.
The non-transmitting side is not affected (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
observer can transmit at the same time - either on
separate radios or on the same radio transmitter!
When on different radios, the pilot and observer
will not interfere with each other’s communications.
For example, the pilot can talk to air traffic control
while the observer talks on the FM radio 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
conversation simply by pressing his PTT switch.
Both voices will be heard by the receiving station.
NOTE: Only the aircraft radios and the FM radio
can be transmitted on. The AUXiliary input is for
listening only. It can be used for listening to a police
scanner, monitoring the audio portion of a video
camera, listening to background music, and many
other possibilities.
TRANSMIT MICROPHONE GAIN ADJUSTMENTS
Transmit microphone gain adjustments for both
the FM and the aircraft radios are provided through
two small holes on the top of the SPCC unit. These
adjustments set the microphone audio level going
to the radios during 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 FM Radio Mic Gain Adjustment, however, will
more than likely need to be initially set to your
particular FM radio. This level, once set, should never
need adjustment again unless, of course, the type
of FM radio used is changed. The following simple
procedures take you through the adjustment of the
FM and A/C mic gain levels. If desired, a qualified
radio technician can do this for you.
FM Radio Mic Gain Adjustment can be made
through the hole to the right of the FM radio
interface connector with a small, flat bladed
screwdriver. The basic adjustment concept is
simple. You will be setting the level and clarity of
outgoing transmissions of the FM radio, when it is
hooked up through the SPCC, to match or exceed
that of transmissions on the radio when it is not
connected to the SPCC. To do this, you will need to
transmit and receive on the FM radio to a remote
station. Arrange to have someone nearby with a
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