Strange network connection quality problem with dual sim

[RaoulTeeuwen]

Hello.

My employer gave me a S21 5G phone. I use it with a physical SIM in slot 1 and an eSIM. People told me they had problems contacting me on my SIM1 number. I fiddled around with settings.

If i set 'Network mode' (Settings/Connections/Mobile Networks) for the eSIM to '3G only', network quality for SIM1 shows all bars. If i toggle the Network mode of the eSIM to anything else, the quality drops significantly, probably causing, in areas with less reception like in buildings, the SIM1 to have 1 bar or worse.

Roaming, VoLTE toggling etc doesn't seem to influence this. And the behaviour is repeatable (toggle Network mode influences connection quality bars of SIM1).

Anybody have any idea? Is this a design flaw, with 2 radio modules (one for every of the dual SIMs) that influence each other, leading to lower connection quality?

[cheflaszlo]

ridiculous problem. 2 sim sharing 1 antenna. interfere each other badly, losing gps too. unbelievable 

[Drivemd]

I have a similar problem but worse. I have 2 physical Sims on my A52 5g. When I try to connect to mobile data on the 1st sim which is on auto connect 5g/LTE/4g/3g/2g network, with my 2nd sim on auto connect LTE/4G/3G/2G network, data connection simply doesn't work at all. But when I either turn off the 2nd sim or downgrade the 2nd Sim's network to auto 3g/2g or 3G/2G individually, the 1st sim can connect to my network provider's mobile data normally even at 5G speeds. I dunno if this is a hardware or a software problem. Hope Samsung has an answer for this.