Interesting Polarity Discovery on WRTP54G - Telco experts?

Posts: 2257 · Posted: Tue Feb 21, 2006 7:46 am Post subject:

VonageTPA wrote:

In the meantime, there *IS* an option that the Vonage techs can swap on the RT31P2's to reverse the polarity.

Or, if you have equipment that cares about it, you can get a 2-wire telephone patch cord, because they seem to reverse the polarity most of the time. The 4-wire ones seem to be straight-thru most of the time.

This is interesting. My mother is not on Vonage, she's in a dialup area and gets 24K at best. Given the reported problems that I've discovered with reversed polarity and modems, and how easy it was for a friend in the phone company to fix her neighbor's line to 56K, I'm wondering if her phone company didn't just reverse the polarity on her line. Time to dig out some various patch cables. Worth a shot.

Posts: 1715 · Posted: Tue Feb 21, 2006 11:31 am Post subject:

If anyone does find an actual issue where reverse polarity is adversely affecting their equipment, please let me know. I just received an e-mail from one of the Vonage electrical engineers. He's of the same opinion that I am, that reverse polarity's not an issue, but I know nothing's impossible.

Posts: 533 · Posted: Wed Feb 22, 2006 2:17 pm Post subject:

Unless you have really old equipment, you don't have to worry about the polarity. I doubt you would find any device today that doesn't have polarity protection - basically it makes sure that tip is always more postive.

Posts: 4777 · Vonage Forum **MVM** Joined: Aug 30, 2005 Posts: 4777

That's good to know, but there's a big difference between reverse polarity protection and "no problem". Protection means the equipment won't be damaged, but it doesn't assure that things will work.

Posts: 2257 · Posted: Wed Feb 22, 2006 8:52 pm Post subject:

I'm not saying that the reversed polarity is a problem, per se. My phones don't seem to care one bit. I have heard that some modems may be sensitive to it, and I'm hoping that my mother's POTS line suffers from something this simple and a simple polarity reversal will get her up from 24K dialup to something better.

I don't think this is a real "problem", since so many patch cables reverse polarity anyway, so if Vonage "fixed" it they'd probably break a bunch of gear that has been fixed already (and unknowingly) by using a reversing patch cable. Plus, I don't think anything built recently would care, since it has "autocrossover" detection (to steal the networking term).

But I figured it may be of interest to people with more obscure equipment, fixable by a cheap 2-wire patch cable.

Posts: 533 · Posted: Thu Feb 23, 2006 9:43 am Post subject:

Steve48 wrote:

That's good to know, but there's a big difference between reverse polarity protection and "no problem". Protection means the equipment won't be damaged, but it doesn't assure that things will work.

Not in this case. Polarity protection in this case means the circuitry is designed to work with -48v or +48v.

Not that this matters in the US, but over in the UK, they actually mandate that all telco equipment function properly with either polarity.

Posts: 193 · Vonage Forum Master Joined: Feb 28, 2005 Posts: 193

Maybe the Vonage engineers need to read the last part about line interference. There is also good stuff about voltage on the line in the middle of the page:

http://www.tkk.fi/Misc/Electronics/circuits/teleinterface.html

By the way don't try any of this circuit building at home; don't want to blow anything up Twisted Evil