TELECOM Digest OnLine - Sorted: Re: How Long Can a Telephone Extension Cord Be?

Re: How Long Can a Telephone Extension Cord Be?

Robert Bonomi (bonomi@host122.r-bonomi.com)
Sat, 13 Aug 2005 14:48:47 -0000

In article <telecom24.365.7@telecom-digest.org>, wylbur37
<wylbur37nospam@yahoo.com> wrote:

> Recently, at a Radio Shack store at the telephone accessories section,
> I noticed that telephone extension cords were available in lengths up
> to 25 feet (but I didn't notice any that were longer). Is that
> because 25 feet is the longest you can go before there's a significant
> loss of signal strength?

The issue is not 'loss of signal strength', but 'pick-up of
interference'.

The 'pre-made' cords at Radio Shack, etc. are usually what is called
'satin' cord. Notably, all the conductors are laid out exactly
parallel in the flat cord (same arrangement as 'ribbon' cable', just
with a small number of conductors.)

Such 'flat cable' is much more prone to pick up interference,
etc, than is a 'twisted pair' cable.

In twisted-pair cable, the position of the individual conductors
changes 'frequently' (depending on the 'category' of cable, it may be
centimeters to 10s of inches). This results in the different sections
of the cable picking up the interference *differently*, and the signal
pick-up in the different sections effectively cancel each other out --
with just the 'intended' signal going through. It isn't "perfect",
but it is much *much* better than what happens with 'flat' cable.

Note: Radio Shack, etc., also sells 'spools' (50', 100', maybe 250'
and longer) of 'round' telephone cable -- which _is_ 'twisted pair'
construction. You can easily build-you-own long extension from that.

> And what about people who access the internet via 56K dial-up? For
> them, how long can the extension cord be and still have "clean"
> transmission for error-free downloads?

The authoritative answer for that is "whatever works". *grin*

Seriously, the phone cord _itself_ is a 'non issue'. It is "what
else" that is in the vicinity, *generating* interference, that is the
primary problem.

There are *no* _official_ "rules" limiting length of extension cords
-- and you can always buy a 'coupler' (sold at Radio Shack, etc.), to
join 2 25' extensions, giving you a 50' reach, for example.

Probably the primary reason you don't see cords longer than 25' for
sale is that there would be a _very_small_ market for them. 10' and
15' cords out-sell the 25' ones by a *big* margin -- something like
25:1. I'd expect _at_least_ 10:1 to 15:1 for 25' vs 50'.

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