What is a bridge tap?!
January 25th, 2018 12:24 pm
We are seeing an increasing frequency of people posting on various internet forums about bridge taps. This post covers what they are & how you can avoid their pitfalls. 

Bridge taps are unterminated extensions of the telephone line or loop. They can alter the impedance of the local loop, especially at ADSL & vDSL frequencies. With DC (AC when the phone rings!) voltage the bridge tap behaves like an open circuit (so no effect), but with high frequencies (ADSL & vDSL), the loop becomes a transmission line "stub". This impedance mismatch can cause a wide variety of problems, but typically it causes a reflection of data bits from the tap-point back to the point of transmission. This results in bit errors, or in English, your speed will most probably reduce.

So how do we avoid this? The easiest way is to fit a filtered faceplate to the master socket. This will issolate all extensions from the DSL signal so they can no longer affect it (centralised faceplates remove the DSL signal from telephone extensions).

But what if you must have your modem or router on an extension? Won't that be a bridge tap? NO!

Read back what we said above, a bridge tap is an unterminated extension! Your extension WILL be terminated with the modem/router! In other words you can quite happily use a vDSL/ADSL extension kit without killing your connection.

This all assumes your master socket and extensions are wired up correctly. If for example you have an extension that T's off BEFORE the master socket then again this would be a bridge tap and BAD for DSL signals.

This customer followed our advice......

"Thought I’d drop you a note that I followed your instructions with the kit that arrived promptly and after a little wrangling the results..... an average 28mbs increase over my old speeds using fast.com!!!

Massive thanks again - you can imagine I’m more than pleased :) "