Vox Operation - Kenwood TS-120S Operating Manual

4.2.1. FINAL STAGE PROTECTION
The TS-120S(V) features a VSWR protection circuit to
protect the final-amplifier transistors. The circuit in the TS-
120V is different than the circuit in the TS-120S.
(1) TS-120V
If the VSWR increases because of improper antenna im-
pedance, the protection circuit activates to prevent the final-
stage transistors from being overloaded. In this case,
transmitter output power is reduced.
(2) TS-120S
Three different protection circuits are designed into the TS-
120S
!) The same VSWR protection method as used in the TS-
120V is used in the TS-120S. That is, the final-stage
transistors are protected by detecting VSWR of the
antenna system and automatically lowering transmitter
output power if the VSWR is too high.
ii) When the heat-sink temperature rises, a detection cir-
cuit activates a cooling fan. Under normal conditions,
this cooling fan sufficiently cools off the heat sink
radiator.
iii) The heat-sink temperature could rise abnormally during
long transmissions, if the area adjacent to the heat-sink
is blocked. In this case, the TS-120S automatically
returns to the receiving mode, and transmitting is not
possible until the heat-sink cools to the proper
temperature.
NOTES:
1. If transmitter output decreases due to activation of the
protection circuit caused by high VSWR, recheck and
retune the antenna system carefully.
2. When the cooling fan starts to turn, determine that ade-
quate air flow is possible in the heat-sink area.
(3) Operation of the Cooling Fan
The cooling fan operates when the heat-sink temperature
rises, and it ceases to operate when the temperature
decreases to normal. The heat-sink is made of die-casting
aluminum and is actually the rear panel. It must be kept
clear of surrounding objects, in order that heat will dissipate
easily.
The cooling fan is designed to operate when the heat-sink
temperature is at a specific level, regardless of whether the
unit is in transmit or receive mode.
4.2.2. MIC GAIN CONTROL (Fig. 4-5)
This control adjusts the microphone input level. When using
the TS-120S(V) in USB or LSB mode, connect a microphone
and set the standby switch to SEND (antenna or dummy
load MUST be connected).
Set the meter switch to ALC and speak into the
microphone. Adjust the MIC GAIN control so the meter
does not deflect out of the ALC zone at signal peaks.
12
The TS-120S(V) accepts either a low or high impedance
microphone (500 2 to 50 k&2). When using a low impedance
microphone (500 {2) the MIC GAIN control should be ad-
vanced higher than when a high impedance microphone is
used, while observing the ALC meter.
e@ ALC (Automatic Level Control)
The ALC monitors the transmitter final stage output to
minimize distortion in your transmitted signal. It
automatically adjusts output to an optimum level.
Pointer should not deflect beyond
ALC zone at signal peaks.
Fig. 4-5 ALC Adjustment
4.3 VOX OPERATION
4.3.1. VOX SWITCH
VOX (voice operated transmit) is used to switch the TS-
120S(V) into transmit mode by your voice. Depress the
switch ON and speak into the microphone. The transceiver
automatically switches to transmit mode (the MIC control
should be adjusted in advance as explained in Item 4.2.2).
Both the send switch and the MIC P.T.T. switch are left in
the REC position.
4.3.2. VOX GAIN CONTROL
This adjusts the VOX circuit sensitivity. Speak into the
microphone at normal voice levels and adjust the control.
Clockwise increases sensitivity, allowing transmission with a
low voice level. Transceiver operating condition can be
checked by the sound from the speaker. When the speaker
is silent, the transceiver is in transmit mode.
Note that if the control is advanced too far, the VOX circuit is
"tripped" by ambient noise.
4.3.3. ANTI-VOX CONTROL
This prevents the VOX circuit from being "tripped" by sound
from the speaker.