b. There are five distinctive audible indicators that you need to become familiar with. These audible
indicators will let you know what the operational condition of the radio set is.
(1) Low battery indicator. A repetitive clicking sound will be heard over the attached audio
accessory when the battery voltage has fallen below 20 volts and when the battery is nearly exhausted. It first will
be heard during a tune-up or voice transmission and will stop when you release the push-to-talk (PTT) switch. At
this point, the battery has enough power left in it to let you transmit very briefly. When the alarm sounds
continuously even while in the receive mode, you must replace the battery and have the drained battery recharged.
(2) Power output indicator. If while you are transmitting you hear your voice in the handset earpiece,
you are hearing what is called sidetone. If you hear this sidetone, the radio set is putting out an RF signal. The
absence of this sidetone indicates that you are not transmitting or you have a bad handset.
(3) Tuning indicator. If you have the ANT SEL switch in the BNC or WHIP position and the radio
has been turned on or you have just changed frequency, the tuning operation will begin the first time the PTT
switch is pressed. A continuous 1-kilohertz (kHz) tone will be heard in the handset. When this tone starts, you
can release the PTT switch, and the radio set will tune itself. The tone will be heard until the radio has tuned
itself. When the tone stops and the noise level increases, the antenna and radio set are matched. If the tone stops
but the receiver noise level does not increase, the radio set is bad.
(4) No-tune indicator. If the tuning tone continues for a very long time (8 to 12 seconds) and a
beeping tone is heard after the tuning tone ceases, the tuner has failed to tune and a tune fault has occurred. Shut
the radio off, and turn it back on. Press the PTT switch again, and see if it will tune. If you get the beeping tone
again, you have a faulty antenna or the antenna is not suitable for the selected frequency.
(5) VSWR indicator. If while you are transmitting (or before you attempt to transmit after you have
been receiving) your antenna is changed (or the immediate environment of the antenna is changed. Its impedance
will change and a high VSWR will result. The tuner will measure the VSWR when the PTT switch is pressed and
will retune if the impedance change is permanent. A short beep will be heard at the beginning of the transmission
if the VSWR mismatch was temporary. There will be no retune in this case.
c. Table 4 gives you a handy guide to use when the radio set AN/PRC-104 is not operating properly.
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