testing Phone Jacks

Discussion in 'General Electronics Chat' started by electronewb, Dec 4, 2012.

  1. electronewb

    Thread Starter Member

    Apr 24, 2012
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    Is there a way to test phone jacks to see if they are actually "on line"? I have quite a few phone jacks to test at work the way I do it is I just grab a crappy phone and see if there's a dial tone on the line but I need something more compact that I could carry in my pocket. Would a phone cord cut in half with a resistor and a LED in series across the red and green wires work? Basically the phone jacks go to a central office where they get patch so I need to determine which ones are patch and which ones are not.
     
  2. Austin Clark

    Member

    Dec 28, 2011
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    If I had to guess, I'd say the LED idea will work. Of course, it all depends on the actual output (the amplitude mainly). I'm not familiar with the wires though. I assume red is Positive and green is ground though.
     
  3. KJ6EAD

    Senior Member

    Apr 30, 2011
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  4. electronewb

    Thread Starter Member

    Apr 24, 2012
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    I've seen those before but I'm wondering if what I describe would work. It's more for the fun of building it than anything else!!!!
     
  5. electronewb

    Thread Starter Member

    Apr 24, 2012
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    Yep it works I used a 3.6k resistor 1/4W but I need to use a 2W
     
  6. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Just be careful that the line doesn't ring while you use a simple circuit. Ringing a phone puts [in the US] a 90 VAC 20Hz signal across the line. This probably would blow your LED. Confirmation anyone?
     
  7. #12

    Expert

    Nov 30, 2010
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    True. A ring signal is higher voltage and lower impedance than the DC level at, "wait for off hook" or "dial tone". 90 to 105 RMS IIRC. While we're at it, the DC during "wait" is the opposite polarity of when it's in "dial tone".
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Also keep in mind that when using a simple LED solution, to only use it on a POTS line (Plain Old Telephone System).

    Newer digital systems, such as those used in offices aren't compatible and many can react badly if a digital bus is suddenly used as a power source.
     
  9. Externet

    AAC Fanatic!

    Nov 29, 2005
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    These were given away in a candy jar on the counters of RadioShack stores years ago.

    -----> http://www.qsl.net/kc9asi/led/tester.jpg

    -----> http://www.qsl.net/kc9asi/led/index.html

    Lights up if the line is alive; it is nothing more than a bicolor led -no resistor-, shows red if reversed and green if not, smaller than a pen. You can build it crimping the led direct to standard telephone plug and without the handle, it would be less than an inch long. Works, perfect, I still have a couple.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    A telephone line when loaded with an LED will not ring (with 90VAC at 20Hz) because it is "off hook" and therefore is busy.

    I worked with big office telephone systems for a few years. I demonstrated a "bug" to the Japanese designers: If you dial "9" to get an outside line at exactly the same moment that the line begins to ring then the processor froze and needed a reset.
    The designers couldn't cause it to happen but my customers and I could make it happen almost EVERY time we tried. A software patch fixed it.
     
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Ahh, the old Black Box trick.
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    Remember "in the good old days" you could make a free long distance phone call from a pay phone if you shorted its transmitter to ground with a paperclip wire for one second?
    Remember "in the good old days" you could tie up somebody's phone line if you call them, they answer then you do not hang up?

    Nowadays I get many SPAM phone calls from people who can barely speeky zee Engrish about ducts cleaning. I say, "No thanks, my ducks (quack quack) are nice and clean".
     
  13. vk6zgo

    Active Member

    Jul 21, 2012
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    We get the Indian lady who says,"You have a problem with Windows".
    We say,"No,we just got them washed":D
     
  14. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I would know nothing about such devices. I was a clean-cut kid who NEVER got into phreaking and wasn't a master of ASCII schematics. Plus, that annoying buzz from the ring attempt really messed with a modem connection. ;)
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    I can't remember if I was "A CLEAN CUT KID" so probably I wasn't.
    Sometimes my friends and I did fun and dangerous things that "clean cut kids" never did.
    Our rockets blew up. Our bombs flew very high. My fingers and eyes survived.;)
     
  16. electronewb

    Thread Starter Member

    Apr 24, 2012
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    Just found something interesting I was testing the line for my little tester and was only getting 9VDC I realized that my wife was on the other line upstairs talking on the phone so I assume that a phone off the hook uses around 50VDC. Could I grab a small speaker and listen to a conversation by wiring the speaker to the red and green wire of the phone?
     
  17. #12

    Expert

    Nov 30, 2010
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    It's easier than that. Just pick up another phone on the same line and listen. It already has a speaker in it and it is connected to the phone line. If you connect an 8 ohm speaker, you will short out the signal.
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    The speaker will short the signal and will also short the 9VDC that powers the phone so the phone will not work (unless it is an extremely old phone that has no electronics in it).
     
  19. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Or you can use one of these: http://www.mcmelectronics.com/product/72-6966

    I was tracing a cable in a large factory office several years ago, I put this probe (inductive amplifier) next to a cable and could hear a phone conversation. Several years later I was telling a friend about it, and we gave it a shot. Found out it doesn't work on digital phone systems :(
    It also works on the wiring for the PA system.
     
  20. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Ideal makes an ABS (Almost Butt Set, no talk ability), that you can listen to the phone line without making connections (inductive pickup). You can also dial a test number to find out the number you are assigned through the provider, etc.

    To use any phone line as a ... Phone, you'll need a butt set, very useful, but not cheap or extremely portable.
     
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