>----------
>Da: John Lin - TAO[SMTP:LinJohn@mail.dec.com]
>Inviato: mercoled=EC 28 maggio 1997 3.54
>A: 'si-list'
>Cc: 'johnlin@mail.dec.com'
>Oggetto: need help for networking loop back, Thanks
>
>Hi,
> For testing network system on PC, we plan to design a device -- "loop
>back". With this loop_back, we can run burn-in program on PC and test
>the stability of the network system. Currently, we need to use
>100 meter long cable to work as the loop_back.=20
>
>My question is how to design the loop_back without using 100 meter long
>cable and still have the effect of 100 meter cable?=20
>
>My idea is that using two short cables, 50cm, with resistors to
>simulation attenuation of long cable shown below:
>
> R1 : about
>8.55 ohms to works as DC resistor for 100 m cable.
> L1 (50 cm ) =20
> >--R1-------------------+ Because of
>Characteristic imped. Z0 for cable is 100 ohms
> | R2 // R3 =3D
>100 ohms (to avoid reflection).
> <---------------R2 +---+ =20
> L2 (50 cm) | R2/(R2+R3) =3D
>attenuation of 100 m cable.
> R3
> |
> ----
> / / / (gnd)
> =20
>Could somebody tell me if my idea is correct or not?
>Thanks in advance.=20
>
>
>John Lin=20
>CAE of EDA dept, PC Engr.=20
>Digital Equip. Corp. Taiwan
>Email: linjohn@mail.dec.com
>TEL: 886-3-3900000 ext. 2565
>
>