I just want to raise a point about using the Loop Antenna Amplifier + with a variable supply.
It will be possible to reduce the gain by reducing the voltage applied to the amplifier.
The reduction in gain below 5 V is caused by the bias voltage dropping to a barely workable level.
The amplifier would be prone to generating cross-modulation and intermodulation at that point and I wouldn't recommend it.
For the best RFperformance run the amplifier with a bias-tee at 12 V and add an external attenuator between the amplifier and the receiver if you want to reduce the overall gain.