Are there an special provisions needed for DSL and caller ID to exist peacefully together?
My parents are getting DSL, and plan on getting caller ID in the future. I am under the impression that they must have an external DSL splitter (or filter) for caller ID to function correctly. Is this true?
Same rules for alarm systems and TDD? Please set me straight. Thanks, Tim C.
None. A phone line passes all frequencies the cable is capable of handling and standard telephones use just a small part of the frequency spectrum available (~300Hz - 3400Hz), which are just VOICE FREQUENCIES. Caller-id uses this bandwidth to receive its info from the exchange, which is (usually) sent as a 300bps modem data string between ring signal 1 and ring signal 2.
DSL uses frequencies way above human hearing so it does not clash with Caller-id or in fact ANY Voice Frequency operation. These are HF and VHF frequencies
The "DSL Filter" that is needed is simply to remove the DSL HF & VHF from the line, before the voice LF signals are passed to the telephone hardware, as some older telephone H/W does not like the DSL frequency signal present in what they see.
No, it can be an internal or external splitter, it won't matter to caller-id as it operates strictly within the LF signals that standard telephones use. Consider a Caller-id device as if it was just a standard telephone, so it should be AFTER a splitter/filter, just like a standard telephone. My preference is to use a single external splitter for all the phones in the house and take the ADSL signal off the line before it reaches the DSL splitter.
This is where it gets tough, it all depends on exactly HOW the alarm system works (I am not sure what a TDD is but will assume its like an alarm that needs a "clear line" to operate). Some alarms MUST have a clear line to work, so they intercept the cable coming into the house and BREAK the line at that point when the alarm is triggered, so they can guarantee they have a working telephone line that can reach the exchange. In this case DSL should still work, unless there is something specific in your Alarm system that says it cannot. I suggest you contact your Alarm manufacturer to clear this point up, BUT don't be surprised if the Alarm people say "whats DSL"?