I'm using a passive antenna system to bring cellphone signals into my home where signals are too weak. Even with my passive repeater, sometimes to send texts I have to walk over to the antenna outside the window to get the text to go. I'd like to increase the signal going out, but inserting a gHZ amp would likely reduce the signal coming in. I could solve that by adding another pair of antennas as a receive setup, but that's cumbersome. I'm considering instead buying a bidirectional amp made for this purpose. So now I'm wondering, how do those work?

Are they true duplex with simultaneous transmit and receive? Or do they sense when my phone is transmitting and amplify outgoing signals during those intervals and otherwise amplify only incoming signals?

Att and sprint used to offer repeaters that would link in with your broadband.

Jason

This doesn’t answer your question, but is relevant to your problem if you have Verizon as your provider, as I do.

We live on the edge of the boonies and have the same issue with coverage inside the house.

When I called Verizon a few months back to see what might be done, they sent me, free of charge, a device that plugs into one of the Ethernet ports on my AT&T Broadband modem and automatically solves the problem. It takes care of calls and text messaging, apparently without using any not my mobile data allowance.

That is what I was referring to, a micro repeater.
Jason

Yes, I knew such things existed even before calling them.

The surprise was that they sent me one free and quickly.

I'll check into the broadband repeater. I'm on ATT. They have WIFI calling which my phone supports, so I have no problem in the house with dropped phone calls on my end. But WIFI calling doesn't support texts.

I suppose I could look for a texting app designed for whatever signal is stronger, but I don't want to have to learn new software, setting up auto-replies, etc.

Really, I can solve that issue and I do appreciate the suggestions. What I really want to know is how bidirectional amps work so I can see about making one just to see if I can. This is one of those cases where practicality can be deferred. I want to learn.

Re the OP, I looked up patents and found three ways bidirectional amps can work. One uses a fast switch, faster than audio, to alternately switch two amps in and out, so one amp is never on while the other one is.

Another works by using parallel diodes to create high impedance load for incoming signals and low impedance load for outgoing. I can't see how to implement that.

A third works by using duplexers and circulators on each port. I know what a duplexer is, but what the heck is a circulator? I belief this is the one that uses phasing to prevent unwanted feedback.