RE: [SI-LIST] : DC isolation between CATV/HDTV equipment? XFM or Cap?

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From: Jason Xiao (jxiao@riverdelta.com)
Date: Wed Nov 01 2000 - 07:35:14 PST


"Others" meant other heandend equipment. They can be Hybrid Fibre
Coax/Copper
cable plant with chasis ground of other routers (their internal analog/RF
and digital grounds may be tied to it soemhow to dump their noises?).

-All these headend equipment (router/switches/cable-plant/distribution
network)
are connected by coax copper cables/HFC. Natually the grounds (common
chasis)
of all are connected together by the coax cable shielding.

Recently, our routers are required to provide DC isolation from other
heandend equipment
for safety (DC surge from environment -- neighbouring electronics etc)
and noise immune purpose...

Many thanks,
Jason

-----Original Message-----
From: Boris Yost [mailto:yost@rainbowdisplays.com]
Sent: Wednesday, November 01, 2000 10:17 AM
To: Jason Xiao
Subject: RE: [SI-LIST] : DC isolation between CATV/HDTV equipment? XFM
or Cap?

What's the nature of the "others"? High-speed digital, cheap digital,
low-level RF like TV cable, or what?

-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Jason Xiao
Sent: Wednesday, November 01, 2000 9:37 AM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : DC isolation between CATV/HDTV equipment? XFM or
Cap?

How does CATV/HDTV headend equipment provide DC isolation from others?

Isolation Transformer usually does not have enough bandwidth
(from 50MHz to 900MHz).
DC blocking cap does not provide enough isolation (1.5kV?).

I am also trying to separate our Chasis ground (most analog/RF ground
tied to it) from others (connected to us through long 75 ohm coaxial copper
cables.
But RF noise from others will see no ground (behave as an antenna to
radiate).
So, I end up to need a cap to tie the grounds?

Mini-circuits TC1.5 or TT1.5 (75 ohm to 50 ohm)to provide DC
isolation instead of DC blocking cap. I could not find any Isolation
XFM to cover my higher end frequency range (upto 900MHz).

I am a microwave/RF circuit designer with very little signal-integrity
experience.
I just found this group yesterday. It's very helpful one.
Any comment and experience will be highly appreciated.

Jason Xiao
978-858-2393
jxiao@riverdelta.com

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