Cat 5 wiring issue 1

[roofer]

I have wired up two networking jacks approximately 30ft apart. They are wired in parallel sharing the same Cat 5 cable. Only 1 PC will be connected to one of the two jacks at any given time.

Here is a brief schematic:

http://12.217.174.187/schematic.txt

jack1 and jack 2 share the same wires for pins 1-8. If I connect PC 2 to jack 1, I can ping PC 1 but if I connect PC 2 to jack 2 there is no reply when PC 2 pings PC 1. There is continuity for all wires 1-8 from jack 2 to the network hub along with lit link lights on both ends. I can not figure out why the two computers cannot communicate. I can only hypothesize that wire between jack 1 and jack 2 is somehow throwing the communicating frequency out of phase?

 

[DogToy]

The NIC and hub port provide the line termination. With the 'spur' to the second jack there is no termination so will give a nasty reflection when using jack 2.

 

[Heydave]

You can make a terminator for the jack that is not in use by putting a series 0.1uf monolithic cap and 100 ohm resistor on each pair. Put the leads of the components directly into the modular plug to keep the lead length short and connect the remaining leads of each pair termination next to the component body. The two pairs of interest are on pins 1,2 and 3,6. The other pairs are not generally used. How well this works will depend on how good your jacks are terminated.
The best jacks are those with punch down connections that allow the pair twist to continue roght up to the connection. Jacks that have screw down terminations end up seperating the pair conductors causing a change in impedance at higher frequencies. If bad enough, this change in impedance will look like an open circuit at high frequencies. When a pulse encounters a higher impedance, it is reflected back in phase. Depending on the length of the transmission line, it can reach a branch point in time to cancel the next pulse.
The branch point itself can also be a problem because it parallels two impedances. This is a lower impedance and reflects pulses 180 out of phase. Your parallel jacks create just such a situation. Again, the wiring should attempt the maintain twist right up to the splice. You could add 25 ohm resistors in series with each leg of such a splice to try to compromise the impedances and reduce reflections.
My guess is that your 30 ft will reflect pulses delayed about 80 ns making it deadly for networking.
Good luck.

I have some wiring color codes on my web page that might be useful:

http://www.inventgineering.com/telephone_wiring_codes.htm