[Gb-ccb] 1PPS signal specifications

[Randy McCullough]

John,

One caution about treating DC power supply lines with Pi filters
incorporating in-line ferrite beads...

Often times, a DC current through a ferrite bead will partially "magnetize"
the ferrite material, causing its operating point to move well out on its
B-H curve (and possibly into saturation).  This effect can severely
compromise the bead's ability to act as a filter...

This is sometimes dealt with by using special ferrite beads which allow
for both the DC power supply lines AND their respective returns to
pass through the same bead, thereby effectively "canceling" the DC
current and preventing "magnetization"...

Randy



John Ford wrote:

> Martin Shepherd writes:
>  >
>  > On Thu, 4 Sep 2003, John Ford wrote:
>  > > I think a good setup would be a grounded BNC connector, a ferrite bead
>  > > on the center conductor inside your enclosure, and a good
>  > > double-shielded cable between your box and the 1 PPS signal source.
>  > > The cable will be about 22 meters long.
>  >
>  > So a loose ferrite bead is sufficient for this connection, whereas a
>  > pi filtered connector was needed for the signal and control lines. Is
>  > this because the remote end of the 1PPS coax terminates outside the
>  > receiver room, whereas the former lines terminate inside the receiver
>  > box?
>
> No, it's because of the coaxial double-sheilded cable, and the fact
> that the other end terminates in a shielded box.  The receiver analog
> section, where the data cables originate, will not be in a shielded
> box.
>  >
>  > How about the analog power-supply lines? Am I correct that these will
>  > need pi filters, because the power supplies are shared with the
>  > receiver?
>
> Yes, the power supply lines entering the CCB box will need filtered.
> Not because they are shared with the receiver, but because they will
> radiate energy into the receiver room.
>
>  >
>  > Also, you mentioned in an email last week that there would be "a big
>  > fat ground bus" between the receiver and CCB boxes. Are you thinking
>  > of a thick cable (how thick?) bolted to the two cases?
>
> We will use a thick braid (3/4 or 1") between the receiver chassis and
> the CCB box.
>
> John
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