On dedicated shortwave receivers, you will not only find the normal volume control (referred to as „Volume“ or „AF Gain“ or „Audio Frequency Gain“), but the gain can also be controlled before demodulation.
The control of the high frequency gain is called „RF Gain“ or Radio Frequency Gain.
In most sets, this function can be switched off, the automatic control of the gain in the high-frequency stages is referred to as AGC (Automatic Gain Control).
The manual high-frequency gain control is activated in the switch position MGC (Manual Gain Control).
If the RF gain is set too low, weak signals are not sufficiently amplified and demodulated, the receiver appears „deaf“. In some receivers, especially in the commercial and amateur radio segment, this can be recognized by the signal strength instrument showing high deflection.
When you test a receiver for proper functioning, it is therefore important to make sure that the radio frequency amplification or the RF gain is set to maximum. Only in the case of CW reception and overload phenomena on powerful long-wire antennas, the RF gain has to be reduced carefully.
A similar function has the „attenuator“ (ATT or Attenuator) which is sometimes found on low-cost receivers. It is used to reduce the total signal level by 10 or 20 dB in case of overloading due to strong antenna signals in proximity of a transmitter. If the attenuator is activated by mistake, the receiver also appears insensitive or defective.