Indoor Antenna Catches Only 12 Channels: Samsung UE40MU6472, Konig KNT-DBVT-IN20, Options?

Hi,

I have:

TV: Samsung ue40mu6472
Terrestrial / indoor antenna: Konig KNT-DBVT-IN20
15 dB, DVB-T
VHF: 174-230 MHz
UHF: 470 - 790 MHz

Transmitter towards the Palace of Culture and Science - about 4 km.
ERP power [kW]: 17
Polarization: horizontal
Antenna height: 218 m above sea level
Transmit channel: 7 (191.5 MHz)
Azimuth: 79 degrees

Unfortunately, I am limited by the walls of the building (attachment) - a wall, a staircase, another wall + the next floor of the building.
3rd floor in the 6th storey. ul. John Casimir

Square: window
Arrow: transmitter direction

The room antenna catches only 12 signals, of which they receive 4 (Metro TV, WP and other crap - TVP, TVN, Polsat are missing, etc.)
On the coaxial cable it catches the same channels.

It seems to me that the ancestor is too weak. Will it be better if I invest in a more powerful indoor antenna or maybe I buy an external broadband and look for the signal to the north - but I'm also limited by the building (I have a patio view)?
Or do it yourself from a cable and a piece of wire?

A neighbor wrote that he was catching a signal from Raszyn on an ordinary cable, but I assume he has a window to the south.

Any suggestions ?

External antenna.

Direct it then to what direction?

Will be OK ?

http://allegro.pl/antena-telewzyjna-dvb-t-szerokopasmowa-35db-4078-i6670484693.html

If the mesh is rather without an amplifier. There is no chance of a stable reception in this well. Probably the antenna needs to be thrown on the roof.

@Gooes
And there is no cable TV in the block with a social package for a few zlotys?

If not, then the antenna is outside, mesh and try to get something from the reflection from Raszyn.