Thanks to everyone for the info.
After analyzing the entries in this and other threads, I bought a Cybertech 17 dB 1800-2600 antenna (https://www.cybertech.com.pl/p173,antena-dualna-lte-a-4g-17dbi-mimo-1800-2600mhz. html). (Of course, after testing with the old E5372 modem without an antenna placed on a stick outside

The antenna works great (I RECOMMEND) and now I have a very good range in the 1800, 2100, 2600 bands (talking about Play) - for example, for the 2100 band, a real signal increase by about 10dB compared to the E5372 modem on the stick) What it gives a transfer of about 10-30 Mb / s on each of the three above-mentioned bands, of which the 2100 band is the most stable and has the largest upload.
Since I'm using a fairly old modem, I don't have bandwidth aggregation on it. Besides, this modem has a built-in wifi function, but it is quite unstable and does not cover the whole house. That's why I connected it to an old desktop computer and then with an eth cable to the wifi router. I bridged the interfaces in the computer). The whole structure works great, but it is quite crude, so I look for a stationary router that has: wifi, LTE cat> 6 and preferably a GSM gateway (it breaks voice connections at home).
@lake he wrote:
Quote: I recommend Huawei 525. I bought one myself
If you believe the table in this thread:
http://www.bez-kabli.pl/viewtopic.php?p=568952#p568952#p568952, B525 will not allow me to sensibly aggregate the 2100 bands (which for me is the best in terms of stability and upload) so it rather falls off. From here, I will most likely change to the B715. I hope that it will additionally allow me to connect a landline to GSM (
@ matek451 I understand VoIP functionality is cut, not GSM?).
Thanks to everyone for your help and if you had any advice (e.g. something better than B715 from Playa) - listen carefully!
Thanks for all your help so far!
Adam