For starters, there are two basic types: those in metal housings and all
others. Use amps that have metal housings.
Next, beware of bi-directional amplifiers. Yes, there are line amps on the
market that actually amplify in BOTH directions. They are intended for TV
distribution in one direction and the return path is for remote control,
premium services selection, or whatever. I learned this the hard way when
I got a "good deal" on two rather high performance amplifiers via mail
order, and then found that they were bidirectional after I got them. The
real issue is the fact that the bandwidth for the return path INCLUDES the
HF bands! My concern was that if significant HF RF gets into any of the TV
sets, that energy can couple into the coax feed and then possibly mix with
the desired TV signals inside one of the bidirectional amp units. After
all, all circuitry is on one pc board with no separation shields. The TV
path starts at 50 MHz and goes up from there. Luckily, I was able to
uncouple the return path components rather easily, so I kept the amps.
Most line amps I have run across, even those in metal housings, have 2-wire
power cords. That means you have no ground on the housing, although the
housing can still provide a degree of shielding from external fields. I
have noticed that high end line amps, such as those from Winegard, are not
only in metal housings, but really do have 3-conductor power cords. I use
one of those Winegard amps as the first amp in my system, and I have placed
a good high pass filter ahead of it. That's not a cure-all, but does help.
Of course, you may wish to consider placing ferrite beads over line
amp,power cords and over the coax cables entering and leaving such
amplifiers. Remember, most of the commonly available clamp-on beads are
suited best for VHF use, so if you are having problems from HF operation,
you'll need to do some deeper searching to locate suitable beads or cores
(around which you could wind the power cord or coax cables).
Naturally, there are band-specific filters and you may need to place high
pass filters at the input of each TV set, as well as at each amp input.
Hope this helps. Good luck and please share with us your final
04/12/2007 10:35 Subject
AM [RFI] TV Line amplifiers
Are there any good TV line amplifiers that are usable in amateur radio
environments? Or solutions to using off the shelf units?
Thanks and 73
RFI mailing list
RFI mailing list