Re: [A/S] TV Interference

[Rick Kunath <k9ao@xxxxxxxxxxx>]

>>>We have a TracVision dome with coaxial cable connected to the TV.  The 
>>>external regular TV antenna is also connected into the same leadin.  
>>>
>>I am not sure how this may have been done by your TracVision Installer, 
>>but if indeed the external TV antenna and satellite TV output are in 
>>parallel, this is not proper installation practice.
>
>The TracVision cable and external antenna cable are connected to a splitter.  
>Is this what you mean by parallel?

Yes. This is a no-no. (You,re sure this is a splitter and not a remote 
controlled switch? If it is a splitter, it should say so on the splitter 
case.)

For one thing, you have ingress of over-the-air signals from outside 
into a closed coaxial system. Secondly, you have egress i.e. signals 
leaking out of the satellite box and over-the-air out into the 
surrounding area near the trailer. The likelihood that you'll run into 
the law on this is very slim, but the practice is illegal if the 
standard for measured leakage signal strength exceeds the FCC limits 
(I'll bet it does by a wide margin.) Mainly, having the TV antenna 
coupled into the satellite box's output allows things into and out of 
the system, that should not be there, and decreases the quality of the 
television reception.

I'd look at getting this rectified some day. Ideally, in a modern 
satellite television system, you have a LNB (low-noise block 
downconverter) at the dish. This device translates the extremely high 
frequencies used by the satellites to something more manageable and less 
lossy over a coaxial transmission line. This then feeds the satellite 
converter box via a coaxial cable. The output of the satellite box feeds 
your television set on a yet lower over-the-air television channel via 
another coaxial cable, and the satellite box is in fact a small 
television transmitter (assuming that you're not using separate video 
and sound connections.)

>We  disconnected the external antenna and it made no difference.  However, in 
>reconnecting it, we find the interference is less when the furnace is running 
>- perhaps it was not screwed in tightly enough.
 
Could be, or the connector(s) are not properly installed. Did you mean 
here that you unscrewed the coaxial cable from the back of the 
television set, and the noise was still there with no connection to the 
"F" connector on the television set at all?

I can't really tell you much, other than to take a close look and give 
the connectors the pull test. Other than that, when a connector is 
suspect, the only course of action is to have it replaced (a quite easy 
job.) But let's worry about that later. What happens if you directly 
connect the satellite box output to the television without the splitter 
and the external antenna? How's the noise then? And then what happens to 
the noise if you take your hand and close it in a fist over the coaxial 
cable right at the back of the television set? Sort of hold the cable 
like you would a stick. Take your other hand and do the same with the 
power coed at the same time. What happens? (Sounds kooky, but I am 
having you check for conducted common-mode noise on the outside of the 
coaxial cable and the power cord.)

><<If you have a small portable battery operated radio, you might use it as 
>a sniffer on FM on an unused channel.>>
>
>What do you mean by an "unused channel"?  
 
Find a spot between stations where there is just noise. You know, the 
rushing sound of pure in-between-the-stations static. Listen for your 
noise over the sound of rushing of the static. If the noise is there, 
you'll hear a noticeable regularly timed sort of buzzing or sparking 
sound. If yo move the radio around, you'll be able to tell where the 
noise is loudest, and more importantly, see if it is there outside the 
trailer. That's what I am most curious about.

Hope I am not confusing you :)

Rick Kunath
WBCCI #3060