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Re: [RFI] TV Line amplifiers

To: <w70m@comcast.net>, <rfi@contesting.com>
Subject: Re: [RFI] TV Line amplifiers
From: "Tom Rauch" <w8ji@contesting.com>
Reply-to: Tom Rauch <w8ji@contesting.com>
Date: Fri, 13 Apr 2007 21:43:12 -0400
List-post: <mailto:rfi@contesting.com>
> Are there any good TV line amplifiers that are usable in 
> amateur radio environments?  Or solutions to using off the 
> shelf units?


Assuming you are using them for TV applications there are 
many good line amps. I used to do systems engineering for a 
company in Ohio that had dozens of head ends... with some 
very close to broadcast stations. The bi-directional 
10-40MHz pass-through amps have never been a problem.

We used Winegard distribution amps http://www.winegard.com/ 
and in larger systems  Blonder Tongue amplifiers 

I think the good Winegard amps are out of production now.... 
but you can find them on eBay.

I have a complex home antenna system and have no problems at 
all. The key is to not have excessive common mode RF in the 
system, but then a good lightning protection system also 
largely eliminates RF common mode issues at HF. When you 
cure the RFI the lighting issue also largely goes away. 
You'll find nearly all TVI problems are not related to 
differential signals on the coaxial lines. Being so the HF 
feedthrough is almost always not an issue, and if it is a 
simple high pass coaxial filter will cure it. TVI in coaxial 
systems, even MATV systems, is almost always caused by 
common mode currents that flow between the antenna system 
and the power mains.

I don't have TVI filters in my system but I do have single 
point grounds for power mains and coaxial cables at every TV 
set and at my "head end".  My head end has channel 4 traps 
that allow our the Direct TV satellite system to feed all 
the TV sets in the house on channel 4 .

My home system has VHF/UHF amps used as the preamp. The TV 
antennas do NOT have amps on them, they come down through 
coax to the small distribution amps that act as "preamps". 
They have good enough noise figures that the system limits 
on external noise and I am in a quiet rural location. The 
actual "pre-amps" I use are  Blonder Tongue ZTA-15 models. I 
do terminate the unused band with 75 ohm terminations when 
dual band  amplifiers are used on single bands like VHF 

My system is TVI-free with 1500 watts from multiple HF 
transmitters, and there isn't a single low pass or high pass 
anywhere in my system. My 40 meter and up antennas are about 
250-300 feet away, and my 160 4 sq antenna has an element 
about 60 feet away.

73 Tom 

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