[RFI] Digital TV Problems

dgsvetan at rockwellcollins.com dgsvetan at rockwellcollins.com
Wed Apr 2 16:44:17 EDT 2008


An interesting problem, especially since I heard recently that some 
community CATV systems are planning to run digital video on CAT-5 lines 
around town.  That's a truly scary thought.  I have heard of one system in 
another town that is working, but they did use SHIELDED CAT-5E cable 
(verified by visual inspection by hams).  In your case, a few questions 
come to mind:

1.  What is the orientation of this one problem set  relative to your 

2.  What is the connecting device between the TV and the phone lines?  Is 
it a passive balun or an active device "converter" box?

I saw K9YC's reply to your inquiry.  Read and heed the info from his web 
site.  The grounds you have are very nice and good for system protection 
from lightning damage, but this is strictly an RF overload problem 
somewhere.  If the TV was good on an outside antenna before, it is 
probably not the set that is the problem now.  You should concentrate your 
efforts on the interface between the TV and phone lines, and don't forget 
that if you use ferrites, be sure they are appropriate for the frequency 
bands you are using. 

Please keep us informed on your progress, and best luck.

73, Dale


DGB <blueheron at Bayland.net> 
Sent by: rfi-bounces at contesting.com
03/31/2008 07:18 PM

rfi at contesting.com

[RFI] Digital TV Problems

I've recently had  subscribed to a service thru the fone lines that 
include TV and Internet. I've had the internet thru it for a long time.

I have 4 tv's in the house hooked to this system.

My shack is in a separate building but still about 30' from that problem 
tv. I've a good single point grounding system that is all connected to 
the tower, the service here in the shack, and the house's service. It's 
all connected undergnd with 2" copper and gnd rods every 16' (over 30 

Recently I've been getting into the TV when xmtg but just one of the 
tv's. My signal scrambles the digital image, like tiling.

 I never had that problem when the tv had an outside antenna, even when 
running legal limit. I've put several clamps-ons on the problem tv. I 
also have a cat5 and telephone cable coming out here to the shak 
underground and have clamp-ons on them as well.

Where do I start?

Thanks ... 73 Dwight NS9I

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