On 7/7/2018 12:41 PM, Richard (Rick) Karlquist wrote:
Interesting paper, lots of stuff to absorb.
My comments here are about the relationship between noise coming in on
the antenna and circuit noise. FWIW, I know this material well, but find
the way the material is presented difficult to follow. Pity the poor guy
who doesn't already know it. I view this as a teaching failure, not a
technical one.
One important error -- for no degradation of signal to noise ratio by
circuit noise, the margin between circuit noise and noise from the
antenna at the input stage must be 10 dB, not 3 dB.
I certainly agree with your comments about preamps with excessive gain,
and although I'm not a student of preamp design, my distant memory is
that gain is one of the important compromises in achieving a low noise
figure.
One of the issues that must be addressed with low output antennas is,
depending on the noise environment, antenna sensitivity, and feedline
loss, whether the preamp should be at the antenna or can be in the shack.
Another question about the presentation is the validity of the noise
data -- how recent is it? In most of the developed world, noise levels
have increased significantly over the last decade or two with the near
universal use of switch-mode power supplies, solar systems, variable
speed motor controllers, leaky CATV systems (especially the HF signals
used for "backhaul" data from consumer to the system). A few years ago,
radio broadcasters asked for a serious study of the increased noise
level, especially on the AM broadcast band.
73, Jim K9YC
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