Thanks for your suggestion, signals decreased but didn't disappeare. I was watching SDR spectrum with a mobile device while I was shorthering the cable.
There are still some strong signals at some frequencies.
Even at those frequencies they are not, the noise is at very high levels around -80 or -90 dBm below 30mHZ.
A λ/4 CB antenna has a much better reception and less noise at all frequencies below 30mHZ than loop antenna amplifier.
This means I can't use the amplifier, unless you have something else to try.