Its to prevent 'earth loops' and avoid issues with DC and low
frequency AC on the coax screen - usually its found only on tx or rx
end- not both- depends on the installation which practice is followed.
Telcos tend to solid ground at the send end and cap ground at the rx
end. And yes- it can make things worse-again depending on the
installation. If you have the option of hard ground or cap ground at
both ends you can select which combination gives the best result.
This is usually only an issue with long runs of coax cable.
DaveB, NZ
----- Original Message -----
From: "Joop" <l...@xs4all.nl>
To: "Joop" <l...@xs4all.nl>
Cc: <time-nuts@febo.com>
Sent: Wednesday, July 21, 2010 11:46 PM
Subject: [time-nuts] Function of cap to GND in isolation transformer
circuit
Hi,
I noticed in several circuits that the 10MHz isolation transformer
in
input and output circuits have a 6.8nF or 10nF capacitor to GND. How
necessary is this for suppression of unwanted signals? Is the
transformer itself not sufficient? I would expect common mode issues
to
be a bit worse with the cap in place.
The circuit I refer to can be seen here:
http://www.uploadarchief.net/files/download/cap2gnd.png
The first one is an output as described in the Efratom FRK manual,
the
second one the input in the TADD-2 manual.
Cheers,
Joop
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