Verizon DSL works okay (Internet drops out about 3-5 times per week). Now I want to add FAX to the same line.
Do I need to install a special filter/splitter?
With DSL, all devices except the modem must go through a filter.
Multiple devices can use the same filter. When i had DSL, I had one filter installed in my basement between the incomming line and all the phone jacks. The DSL modem got a phone line that was split off the incomming line before the filter. The key thing is to make sure that everything excpet the modem goes through a filter.
You WILL need a filter between your FAX and the phone line. The modem inside a FAX works much the way a dialup modem in a computer works. It uses the frequencies reserved for phone voice traffic over the local line. These are the low end frequencies.
The DSL modem and another DSL modem located at the Verizon switching office use the high frequencies. An unfiltered FAX could disrupt DSL data transmission, and DSL could disrupt an unfiltered FAX.
I presume that the DSL modem inside the home gateway and the other one at the switching office each has a high pass filter in order to block out the noise and traffic from phones and devices like FAXes.