How connect transciever to rj45 with magnetics

Thread Starter


Joined Apr 14, 2021
Hello everybody!! i would like to connect a max22500e transciever to an RJ45 port with magnetics like J1011F01PNL how can i connect them? how do I connect the CT pin? (the transciever in this case transmits the data). Thanks to everyone and have a good day.
Last edited:


Joined Aug 21, 2008
The old electronic signal switching office where lived in my teen years (may have been replace in the intervening 50+ years) expected the customer's phone to look like 600 ohms at audio frequencies, so I used transformers with 600 ohm windings. I also AC coupled them to the telephone line and was sure to disconnect from the line when not using it.

There is DC on the phone line so be sure your capacitor is correctly polarized. I think I used 2 uf non-polarized capacitors in one project.

The ring signal (they had electromechanical bells those days but I doubt the signal protocol has changed) was 90 VAC riding on the 48 volts DC that was normally on the line. That suggests that you need to add a clipper to limit the audio voltage going into your transmitter.

Here are some circuits, and you can find plenty on the internet.


Remember, be kind to your telephone company. Don't put excessively high amplitude audio signals on the lines and don't draw DC current from the lines (I had a meter to display voltage, it drew 500 uA but that was enough for them to send somebody out and snip my wires).

Deleted member 115935

Joined Dec 31, 1969
max22500e is a100 Mb/s RS485 / RS422 half duplex transceiver

You answered yes to is it a phone patch,

please can you elucidate, is it a phone or a RS422 or a RS485 ?

If its RS422 / RS485, I understood these were / are DC coupled systems,
as such a transformer would seem to be "a problem"

If it is RS485 RS422, note there are chips that give you the isolation that a transformer would give you