FM Antenna Options for Hager Berker Radio: Improve Reception with Amplifier & External Antenna

Hello. Probably a trivial topic, but it wants to save time for experiments.
I have installed the Hager Berker radio at the client's place, unfortunately the reception from the built-in antenna is practically none. The rado has an output to an external antenna, but has no screen. I would like to use an external antenna with an amplifier because after connecting a meter cable as an antenna, the reception is already satisfactory. I have both the UTP and the concentrator installed to the place of the antenna installation. I am asking for hints.

You, at the client's, and about such ... ask? Jokes?

No kidding, I have not been dealing with RTV for some time and I have a slightly different job and this was done by the way because the client asked not to look for someone else, but if a colleague does not want to help, let him leave unnecessary comments.

Do you have a link to this receiver?
Some photos..?
The company is known to me for its electrical equipment, but I have not encountered their receiving equipment.

Radios under (above) plaster and the author certainly performed the installation. Leave this cable as it receives. These are very sensitive receivers and with an amplifier it may not receive at all.
https://www.google.pl/search?q=hager+berker+r...ctx=1&fir=k0iHgQWa023DPM%253A%252CFW5BPHm4Cw9 %Lv=G=253A%252CFW5BPHm4Cw9 %Lv=G=253A%252CFW5BPHm4Cw9 %Lv=G=253A%252CFW5BPHm4Cw9 %Lv&t=253A%251 0ahUKEwjP5ei3gazXAhXIqKQKHTaLDBEQ9QEI4QEwCA # imgrc = k0iHgQWa023DPM:

This receiver is sensitive, but if it is to be installed, for example, in Węgrów, there will be such interference inside the building that with weak radio signals it will not be ...
When writing about the pictures I meant the "back wall" or a plate with power terminals.
Is there a clamp for the PE wire?

Device in the second class of insulation,
so only LN and L for the start signal. The radio works in the vicinity of Węgrów, where there is a great problem with the reception of any station in the room, and leaving a meter cable sticking out of the cans does not enter the game, it is a room with a strong emphasis on aesthetics.

Oki, that explains a lot, I have come across a similar device from a different company.

I suggest:
- bring a cable near the "radio" at the end of which an external antenna in the form of a simple dipole will be installed;
- at the end of the cable we put an F plug and install a simple RF transformer used as a galvanic signal separator:
http://www.dipol.com.pl/izolator_galwaniczny_5-2400mhz_signal_R48605.htm
Its task is to fully protect both the antenna installation and the power supply and the receiver itself.
The other end of the galvanic isolator is connected to the receiver as follows:
- ground to the ground terminal at the AUX-IN input - the second terminal from the top (it is connected to the "electrical ground" of the receiver, common for audio and antenna inputs),
- "hot wire" to the antenna terminal - the first terminal from the bottom in the same AUX-in input.
If the signal is too strong - which is likely - we will put on an appropriate attenuator.

I will follow the tips and let you know what the effects are thank you for the advice.