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#262046 04/28/10 06:41 PM
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ffej010 Offline OP
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It has been quite some time since I've had to turn-up and test DS0's, but I am needing a loopback plug to test a 56K circuit. I have my circuit terminated on a RJ48S, using R1 on pin 1, T1 on pin 2, T on ping 7, and R on pin 8. I was reading on the forums that the loopback connects pins 1-7 and 2-8. Shouldn't the proper loopback on this actually be 1-8 and 2-7?

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#262047 04/28/10 10:58 PM
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Polarity is NOT important for metallic loopback tests, so it's a "Don't Care". Simply turning around the bits given to you is enough for that level of testing.

Same goes with T1 circuits...same goes with Ethernet.


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#262048 04/29/10 04:49 AM
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Quote
Originally posted by ffej010:
Shouldn't the proper loopback on this actually be 1-8 and 2-7?
Nope...

I’m going to guess you’re probably confusing what the “T-s” and the “R-s” are designating… You’ll see T, R, and R, R1 used to notate the pin-outs. Easy enough to confuse those for “transmit” and “receive” but those names signify Tip, Tip1, Ring, Ring1. A loop-back plug would connect Ring/Tip (the first pair) to Tip1/Ring1 (the second pair.)


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Bryan
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Cars -n- Guitars Racin' (retired racer Oct.'07)
#262049 04/29/10 07:50 AM
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ffej010 Offline OP
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So you loop the Ring (R) side of the first pair (pin 8) to the tip side (T1) of the second pair (pin 2); and Tip side of the first pair (T - pin 7) to the Ring side of the second pair (R1 - pin 1)?

Makes more sense to me to put ring to ring and tip to tip....but I will go w/ what you are saying, you are the experts! Thanks for the info.

#262050 04/29/10 08:52 AM
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Pin 1 = R1
Pin 2 = T1

Pin 7 = T
Pin 8 = R

Jumper pin 1 to pin 7
Jumper pin 2 to pin 8


Each pair works together as a transmit path or a receive path. A loop-back plug turns one PAIR back to the other. Gives the 1’s and 0’s a round trip ride. A loop-back.

Connecting tip to tip1 and ring to ring1 would create a short at the end of each pair. A pair could be tested that way but would be “dead-end” for any transmission tests.


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Bryan
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Cars -n- Guitars Racin' (retired racer Oct.'07)
#262051 04/29/10 07:03 PM
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ffej010 Offline OP
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Thanks for the help and explanation. It is appreciated.

#262052 05/06/10 06:47 AM
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Grab an RJ45 connector and loop pins 1-7 & 2-8 and have at it


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