At 12:38 PM 02/28/10, you wrote:
On Sun, 28 Feb 2010, Mike Morris WA6ILQ wrote:
> 2) the pair that was receiving the problem was a high impedance load
> or an unbalanced load (i.e. one side grounded). Use an ungrounded 600
> ohm winding from a transformer on each end of each pair.
The nominal impedance of a copper pair from CAT5 is 110-ohms, not 600.
--
Kris Kirby, KE4AHR
Disinformation Analyst
I agree with you 100% - but 150 ohm transformers are not as common
as 600 ohm transformers, and we had to solve the problem that day.
We used what was available. Splicing a 1:1 600 ohm transformer into
each end of each audio run fixed the problem.
If transformers with a center-tapped 660 ohm winding had been available
we would have used 1/2 of the winding that was facing the CAT5 cable
since the impedance of 1/2 of a 600 ohm winding (i.e. from the center
tap to one outside end) is 150 ohms.
The ideal transformer configuration for driving CAT5 or CAT6 is one that
has split windings that total 150 ohms that faced the cable and
600 ohms facing the end equipment.
Monospaced font time:
-------------+ +----------
! !
) !! (
600 ohm ) !! ( 45 ohm
winding ) !! ( winding
) !! (
) !! (
) !! !
) !! +------------
) !!
) !!
) !! +------------
) !! !
) !! (
) !! ( 45 ohm
) !! ( winding
) !! (
) !! (
! !! !
-------------+ !! +---------------
The 600 ohms is the audio equipment side.
The two 45 ohm windings in series give 150 ohms (CAT5 CAT6 side).
The inner winding ends can be tied together in normal
use, or used DC remote style for switching far end equipment on or
off or changing modes.
Mike WA6ILQ
