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J. B. Wood · October 8th 09, 11:46 AM posted to rec.radio.amateur.antenna

In article ,
wrote:

For sure. I was on the verge of returning my last analog TV because it
wouldn't get one channel at all, and several others were very poor. But
then I got an idea and added an attenuator at the antenna input. Problem
solved -- got a great picture on all channels. The new HDTV has a better
dynamic range and can put up with the strong signals, so it doesn't need
the attenuator. I'm about 10 - 15 miles line of sight from urban
broadcast towers. I use a commercial TV antenna in the attic.

Roy Lewallen, W7EL

Hello, Roy, and all. The trade-off here is that while putting a pad
(attenuator) in front of the amplifier certainly results in a lower signal
level at the amplifier output being presented to the down-stream
components, the noise figure of the pad+amp cascade is increased by the
attenuator loss (assuming a matched (e.g. 50 or 75 ohms)) pad. If the pad
is placed at the amplifier output the noise figure is preserved but the
dynamic range (usually specified in terms of a third-order intercept
point) of the cascade is degraded. Noise figure and intercept points of
RF distribution system amplifiers used in a shipboard environment have
always been of vital interest to the USN. Sincerely, and 73s from N4GGO,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337