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Joined: Sep 2006
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Joined: Sep 2006
Posts: 3,290 |
Like the man said, the polarity convention in telephony is that ground is positive. Therefore, battery ("hot") is negative. Therefore anytime battery is referenced in text or on an SD we use the negative symbol in front of the number.
There are a few specialized places in telephony where the D-C supply is center-tapped, so that one side is higher than ground, and the other side is lower. In those cases, you will see "-v" and "+v".
Arthur P. Bloom
"30 years of faithful service...15 years on hold"
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Joined: Feb 2010
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OP
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Joined: Feb 2010
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I see. Makes sense. Thank you for clarifying!
Tennessee Technology Solutions, LLC | "Business technology solutions reimagined." | (423) 665-9995 | www.423tech.com
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Joined: May 2007
Posts: 5,058 Likes: 5
Moderator-1A2, Cabling
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Moderator-1A2, Cabling
Joined: May 2007
Posts: 5,058 Likes: 5 |
the only Intercom that I ever used that required an A lead was the 401 A manual intercom. The later 401 B did not need one, nor did any of the dial intercoms (207, 347 etc) that I worked on. As Arthur said, the packaged intercom systems worked very well. You just plugged in a 25 pair cable, cross connected power in and T,R,L and signal leads out.
Very simple, very effective and essentially bulletproof.
Sam
"Where are we going and why are we in this hand basket?"
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Joined: Feb 2014
Posts: 657
Moderator-1A2
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Moderator-1A2
Joined: Feb 2014
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I think I -kind of- know the answer to this... but why are telephone systems positive ground? Since we are on the subject, it would be an interesting thing to know why. Something similar to the cathodic systems used on ships, isn't it? A corrosion thing?
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Joined: May 2007
Posts: 5,058 Likes: 5
Moderator-1A2, Cabling
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Moderator-1A2, Cabling
Joined: May 2007
Posts: 5,058 Likes: 5 |
It's a question I always asked and while I think I got a straight answer once, I'll be damned if I can remember it.
What I heard most often was " electrons flow from the negative to the positive."
At this point in my dotage, I just accept it.
I will also say that I did a buildout for a cell site once and they called for +24 vdc. When I asked why, all I got was blank looks.
Sam
"Where are we going and why are we in this hand basket?"
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Joined: Feb 2014
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Moderator-1A2
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