[RFI] Digital TV Problems

Cortland Richmond ka5s at earthlink.net
Wed Apr 2 22:27:50 EDT 2008


The services that send video over telephone lines will be ADSL and VDSL.  VDSL uses the HF spectrum, though it does not interfere with HF as much as BPL due to the better balance and closer spacing of telephone wires.  ADSL uses the LF and MF spectrum from 100 KHz through 1.1 MHz (perhaps higher for newer versions than the ones I worked with years ago).  It is easy to overload the front-ends of the "modems" used with these systems, and loss of framing will result in interesting effects on digital services.

You may be able to find an ADSL filter ofered for sale at various places.  I don't know about VDSL.  However, when I was working with ADSL some years ago, I found that common-mode noise coming into a modem through the AC power was a problem, sometimes a serious one and I was able to do some good by opening the modem safety ground  with a 3-prong to 2-prong AC adaptor. This is often inadvisable for safety reasons but a filter or ferrites effective at HF may work.

Good luck!


-----Original Message-----
>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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