"James Sweet" wrote in
news:WRHsj.191$sh.156@trnddc07:



One of the cable TV signals might interfere with vital communications,
such as with fire, police or aircraft communications or navigation.

Now that you KNOW that you may be radiating signals that could
interfere with communications, you have an obligation to cease.

Deliberate interference with radio communications is a crime.



Interference in such a scenario is *extremely* unlikely. The power level
is low, and a small unshielded section is a horrible antenna. On top of
that, this would not be "deliberate interference". Putting a connector
on there is a good idea, it's the only right way to do it, but there's
no need for paranoia, there's nothing you could reasonably do that will
cause any undesired interference to anything else.

Try listening on the shortwave radio bands near my house. The noise from
switching power supplies, computers, dimmer switches, TV local oscillators,
power line leakage AND cable leakage makes it impossible to hear any weak
signals using a radio receiver that was quite fine in the 1960's {the Drake
2B receiver}. My Electraft K2/100 does much better but the noise blanker
MUST be used, otherwise only the strongest signals can be heard.

The fault is not the receiver, it is the high level of noises.

I do NOT have nor use cable TV. I get my TV signals 'off the air' with
rabbit ears. I can often pick up sufficient leakage from the cable TV to
view some programs.
There are strong 'herring bone patterns on even the strongest local
stations' due to cable leakage of signals from the cable.

My 2 meter ham transceiver in my car often picks up strong interference on
some frequencies as I drive around town.
Some of the signals seem to be 'point of sale' devices that are radiating
in the 144 MHz band.
Some sound like TV video and some sound like wide band FM.

Of course, some of these are 'mixing products' due to resonant structures
that happen to have non linear conductance {rusty joints) that are picking
up TV and other radio signals, mixing them together and radiating the
products.

I disagree with your assessment of '*extremely* unlikely'. I estimate it to
be "unacceptably likely".

The 'small unshielded section' is not the antenna.
The antenna is the shield which is not connected at one end and the object
at the end of the center conductor.

The shielded cable can be many wavelengths long.

The improper termination at the end causes standing waves. These standing
waves appear on the outside of the coax. The coax radiates.

The entire TV set also serves as a radiating device that is on the end of
that piece of coax.

Take a transmitter and feed it into a long piece of coax.
At the end of that coax, hang a metal plate that is 19 inches by 19 inches.

Feed it with 145 MHz signal.

You will have a pretty effective radiator.

Couple to the metal plate through a capacitor of a couple of nF and it will
still work rather well.

THAT is exactly what you have when you do not connect the shield on that
cable to the TV.

Here is a test you can do with a VCR and two TVs:

Make a 'bad hookup' from the VCR to a TV in one room. Play back a tape on
the VCR [putting a signal onto channel 2 or 3]

Go to another room with a TV with rabbit ears and see if you can see any
signs of the VCR's signals 'over the air'.

I have seen signals from VCR's because people do not realize they are
broadcasting.




--
bz 73 de N5BZ k

I have held FCC 1st class Radio Telephone and 2nd class Radio Telegraph
licences with Ship Radar Endorsement, TEA Certified Electronic Technician
in Radio TV, Audio and Industrial Electronics.

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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