Hi Ron
I would like to share my perspective based on some years of experiments. The
experiment never fails. It is what it is, it can or cannot meet our
expectations.
Let me quote Thomas Edison, he believed that every experiment, whether
successful or not, provides valuable information. He famously stated, "I
have not failed. I've just found 10,000 ways that won't work," emphasizing
that failures are simply steps toward eventual success.
When I built my first 6xBF981 preamplifier for 160 and measured 0.7 db NF my
expectations went to the roof. Wow I have a quiet preamp to work weak
signals on 160m. That expectation becomes a deep disappointment. I almost
hammered the preamplifier when I first listening to it. The sharp frying
noise, hot and very unpleasant. My expectation about a quiet amplifier was
very different from the results I was hearing ,and way far from my
expectations.
I used my Spectrum Analyzer to check what was going on, sweeping with the
track generator I saw a huge peak, 40 db above the reference. This thing
must be oscillating, I was expecting no more than 27 db gain, not 43 db. I
turned off and hit the sac.
Next morning I decided to give another try. I heard a weak signal on 160m,
and for my surprise it was XU7ACY, Peter calling CQ long path. What a
surprise, he comes right back to me, and I logged a new one on 160m. besides
all the noise, the XU7 signal was Q5. I switched to a pair of Nortons
preamplifier following a single Norton with a very good bandpass filter
ahead of it, total 33 db gain. The noise was lower than the 6xBF981, but the
XU signal was not there, or at least not copyable.
I learned that I built a "dream" good preamplifier, I could pull a weak
signal like the same way I experienced working EME on 144 MHz
(PY2DP-1995-1999) before I moved to Florida. Very different from my
expectations the way it works. Bellow the noise there is more noise, like
layers, when you remove one and you can see bellow that level there is more
noise, keep digging and you will see more noise plus a signal. When the
signal is in the noise you will hear the noise too. If you don?t hear the
noise your pre have a high NF and it is deaf.
My 6xBF981 was very important to me since 2010, October 4th, 2010, because I
built it on my birthday. What a nice, unexpected birthday present.
Adrian and I started to play with cw speaker almost the same time back in
2016, but we share information only a year ago. It was a surprise for both
of us. So almost 10 years using the CW speaker as we designed it using 1/2
resonator. My project feeding on the open end, and Adrian project feeding at
the center node. Different design but same concept.
" Dave and Adrian (W0FLS and VK2WF) had 2 different experiences with the
same design of speaker"
Managing expectations allow us to explore another 1000 ways why it doesn't
work, and find what we are looking for, trying to understand the problem
before implement a solution.
" The speaker is radio agnostic. It doesn't care what it plugged in to. It's
just a filter. "
The speaker is a transducer, it covert electrical signal into soundwaves and
it is very, .. a very complex device.
" SNR is independent of the radio, the antenna or anything in between. The
SNR at a dipole is the same as at a 4 element beam. "
I'm sorry to disagree 100%, antenna has directivity, and SNR is better with
more directivity, antenna RX gain is different from TX gain, because the
efficiency, for TX gain time efficiency give you power gain. RX with very
low efficiency can provide a good reception. The simplest way to understand
that is RDF. More directivity = more signal to noise ratio.
I tested 100's of RX antennas on 160m, my notes, measurements, data
collected in the field for each 1 db increase on RDF you gain 2 db in signal
to noise ratio. It is a "empireque" number and not a calculation, based on
practical experience or scientific experiments rather than theory.
You can hear a weak signal using a 4 element beam that is not possible to
hear using a dipole. Just as example, using WSJT to measure SNR, one signal
on my TX vertical was -20 db, the same signal on my Vertical WF was near -10
db. Same signal on my H WF was +2 db SNR, you can check more details here,
and download the presentation pdf.
https://wwrof.org/webinar-archive/high-performance-rx-antennas-for-a-small-l
ot/
We just need to keep experimenting.
73's
JC
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