Jeff Liebermann wrote:

On Sat, 5 Dec 2009 20:30:48 -0800 (PST), Robert Macy
wrote:

Sorry, for jumping in here in the way of Jeff's capable hands,

Grumble...

but
agree with honing in on potential bad connections in that old coax.

There's a fairly easy way to detect bad connections. These invariably
result in coax leakage, where the coax cable magically becomes an
antenna. Find a portable TV receiver, tune it to CATV channels not
OTA (over the air) channels, and sniff around with the portable
antenna looking for leaks (actually called "ingress"). This is
roughly what the CATV people do along the distribution cables using a
pilot carrier. A broken shield, broken connector, and possbibly a
missing termination, should all show up as excessive leakage.


Ingression is external signals getting into the CATV plant. You are
describing radiation' where the signal is lost to being radiated from
the outer conductor, due to poor connections. It is monitored on a
continuous basis on most cable systems using 'Sniffer' or other brands
of monitoring equipment. While the signal is on the video carrier
frequency, it is FM modulated with annoying audio to make it easy to
identify.



Personally, I prefer visual inspection, a TDR (time domain
reflectometer), signal level measurements, or just a pre-emptive
replacement.


Those are OK if you can shut a system down for repairs. Poor
connections in the trunkline can be detected by reading the voltage drop
between the coax and the amplifier housing, splice block or any other
splice in any powered cable. 60 volts modified sine wave AC @ 30 amps
from a CVT doesn't tolerate much resistance without causing hum
modulation or burning up a connector.

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