[RFI] 1500 Watts vs. Radio Shack Amplified Antenna

Ernie Ernie" <ernie@avana.net
Sat, 8 May 1999 00:17:55 -0400

Bill, et al.

Here at my new QTH I am running 1500W to a stack of yagi antennas about 60
off the ground.  My broadcast TV antenna is about 90 feet from the base of
the tower and happens to be pointed about 90 degrees from the direction of
the tower to cover downtown Atlanta from 50 miles away.

I do have a TV pre-amp that is built into the Channel Master Satellite
multi-switch that runs my 18" satellite dish system.  The multi-switch
accepts the local broadcast signal and feeds it, and the satellite signal
to each of the three satellite receivers.  It also connects the Right hand
or the
left hand LNB on the satellite dish to the satellite receivers.

I found I needed an amplified multi-switch  because I had just too much
snow on the picture  when receiving the local TV broadcast stations.
I also ran RG-6 Quad  cable (the good stuff which is unfortunately too
infrequently used) throughout the house to the three separate satellite
Also, all incoming TV and satellite coax cables are grounded to an 8 foot
copper ground rod before entering the house.  The Multi-switch  in
the basement is grounded to a copper water-pipe.  I know this all seems
a lot of work, but I wanted my OWN house clean in case others in the
neighborhood complained!

The other night I really got the HF amp cranked up and asked my wife if she
could tell if I was on the radio while she was watching ER on the local TV
network broadcast.  ( I have not used the amp much at this new QTH.)

She could not tell that I was on the radio.

I do not have any external high pass filters, chokes or torroids in the TV
I do run a low pass filter on the HF rig and amp. I am connected to an 8
foot ground rod
outside the shack.  (on a side note, I rewired the entire house
with twisted pair category 5 cable.  I don't need any phone filters here
either!  )

This to me is a definite sign that not all pre-amps devices are created
equal.  If
the  radio shack amplified antenna is a very high gain device without any
internal high pass filtering on the pre-amp input, it will be nearly
impossible to not overload it.  As you said, when you overload its input,
you modulate its output with your HF signal.

I'd recommend an ICE high pass filter designed to handle both common mode
and differential mode interference, but I doubt you can get it
installed ---between-- the antenna and the built in Radio Shack
preamplifier.  The bottom line is no amount of High Pass filtering or chokes
the --output-- of this RS device will stop the interference.  Once the RF
mixed in a nonlinear device, it is the mixer products that cause you trouble
and not
likely your HF fundamental.

If possible, you might try to get your antennas higher so that they can be
farther away from you neighbor.  High yagi antennas really do contribute
to RFI than low dipoles....remember the inverse square law?

I would recommend that they invest in a good TV antenna system. If
you have one, maybe you can show them yours.

73, Ernie KS4Q

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