Sigtronics SPCC-3 - Manual (Page 5)

4. Receive Volume Controls (REC VOL) are general
volume controls, meant to provide overall lis-
tening level for all three radios simultaneously
- A/C, FM-1, and FM-2. Finite volume adjust-
ments of any individual radio should be done
by altering the radio volume control at the ra-
dio 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 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 head-
phones.*
* Sidetone is a portion of the transmitted voice sig-
nal 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 sid-
etone that you hear in your headset.
The non-transmitting side is not affected (except
for intercom) when the other side transmits. The
non-transmitting side can monitor the transmis-
sions 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 func-
tions 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 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 one of the FM radios to
the ground crew, or vice versa. On the other hand,
they can also transmit on the same radio transmit-
ter. 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.
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 ad-
justments 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 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 adjust-
ment of the FM and A/C mic gain levels. If desired,
a qualified radio technician can do this for you.
FM-1 & FM-2 Radio Mic Gain Adjustment can be
made through the middle and right hole respec-
tively, just to the right of the FM-1 radio interface
connector with a small, flat bladed screwdriver.
The basic adjustment concept for both FM radios
is simple. On a one at a time basis, you will be set-
ting 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 re-
ceive 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
first 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”.
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