I'm designing an embedded modem product using a SocketModem device. I'm having trouble finding out what, if any, protection components I need between the modem module and the RJ-11. Does anyone have any recommendations / suggestions about what realistically I should include. The product will be mainly used in laboratory evaluation work but even so I'd like it to be in accordance with equipment regulations.
TIA.
Rog.
Hi Roger,
Since you didn't get any replies let me give you a few hints.
Most of all you'd have to make sure that no static can destroy things. So a double diode at each input and output, such as a BAV99, would be good. One side to VCC, the other to GND. Static can even build up in a lab, no matter whether they treat their VCT floor right or not. It all depends on the shoes people wear. Dry winter months can be really bad.
If you can afford it from a performance point of view place a resistor between connector terminal and your circuit. On outputs that may have to be a pretty low value.
Then maybe you could run the cable bundle that goes to your RJ11 through a 43 material ferrite, if there is space to do that neatly. That takes care of much of the RFI. And don't forget EMC compliance if this goes into production.
Regards, Joerg
On products I've worked on in the past we used MOVs ( metal oxide varistors ) on the modem lines to suppress transients voltages.
Hi David,
That's a great way of protection. Just make sure that it is compatible and failsafe when someone plugs it into a foreign outlet. Remember all those blown modems where people accidentally plugged into a high voltage hotel PBX? The modem cards heated up and then died within a few seconds.
Regards, Joerg
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