> Are there any good TV line amplifiers that are usable in
> amateur radio environments? Or solutions to using off the
> shelf units?
Rod,
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
http://www.blondertongue.com/Distribution
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
only.
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
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|