8 Receiver RF Gain and Automatic Gain Control (AGC): The RF
Gain controls the sensitivity of the receiver in the radio frequency
stage (the first stage after the receive antenna comes into the set). The
RF Gain control is labelled SENSITIVITY on some equipment.
Unless your equipment manual states otherwise, experiment with the
RF Gain set between 50-75% for normal operation, using the remaining
25-50% only for weaker signals.
AGC detects changing signal-strength (known as fading) in the
received signal, mainly caused by the effect of the ionosphere. AGC
automatically adjusts the sensitivity to compensate for fading signal
strength, presenting the audio stages (loudspeaker and handset) with
a signal of constant level. Some equipment requires that you switch
AGC off before you can adjust the RF Gain/Sensitivity.
If your equipment offers both Fast and Slow AGC, use FAST when
receiving a Signal where the carrier is continuously present (H3E/
AM; FIB) and SLOW where there is no carrier 03E) or where the
carrier is intermittent (AIA/CW).9 AF Gain/Volume: Having set the RF Gain/Sensitivity and AGC
correctly, you should be able to use the AF Gain (may be labelled
Volume) to adjust the volume to an acceptable level in the
loudspeaker/handset. If the AF Gain/Volume is unable to bring the
signal up to the required level, reset the RF Gain/Sensitivity to a
higher level.
10 Clarifier: May be labelled Tune Rate or Fine-Tune (not to be mistaken
for the transmitter antenna coupler Tune at 6 above). Used when a
received signal is loud enough, but distorted due to being slightly off-
frequency (Le. the transmitting station's idea of the carrier frequency
is slightly different to your receiver's idea - resulting in the 'Donald
Duck' effect). The Clarifier can be used to make small, delicate changes
to the receiver frequency to remove the distortion.
Where a carrier is present (H3E or R3E) there will be a tone on
top of the voice Signal being received. You can use the clarifier to
tune into the dead beat of the tone (i.e. lower the frequency of the
tone until it disappears) - your receiver should now be tuned to the
same frequency as the transmitter.
142 THE NAUTICAL INSTITUTE