Greetings Topbanders. . .
There has been some discussion in the Topband community over the past
year about "CW speakers." The CW speaker has had a small but
enthusiastic following relating first hand experiences with the device
remarkably and easily pulling weak signals out of the noise that were at
or below the receiver's real time effective noise floor. I wish to
relate my own experience with the CW speaker.
A little over a year ago as part of my effort to downsize I
decommissioned my station built in 1996 on a very "quiet" QTH on 35
acres in rural Iowa. When I say the QTH was quiet I mean in terms of
very low noise level on 160m. Back then the noise floor on my FT1000MP
was in the -130 dBm range listening on a quarter wave vertical
antenna. At high noon in the winter I could disconnect the vertical
from the receiver and noise would only drop about three or four db, if
that. My four square TX antenna was remarkably quiet to the extent that
beverage antennas rarely offered any improvement in copying weak
signals. It was a perfect place to chase 160m DX. Over the years the
noise floor increased with with the construction of new houses within a
mile or so along with the the flood of new electronic/digital devices.
By the time I decommissioned the station in 2024 the noise floor had
increased a good 10 db or more. However, even at the end my overall
receive capability still remained fairly good. The remarkable Hi-Z
eight circle array (200' optimized for 160) was my salvation.
In June 2025 I moved to a suburban QTH with the usual HOA restrictions.
. . uggh. Fortunately, I had the option of remoting into another nearby
well equipped rural station providing me a good place to continue
operating and chasing DX (CW) on Topband. I began 160m operations with
my usual routine of being on in the evenings for Europe and again on
mornings for VK/ZL/Asia. I continued my long standing tradition of
having QSOs with Topband stalwart and beacon, Adrian/VK2WF. While the
remote station had (and has) noise problems in some directions,
fortunately, the noise floor looking west toward VK was pretty good. .
.about -129 dBm on the west Beverage. During my dozens of QSOs with
VK2WF it became quickly apparent that he was hearing me significantly
better than I was hear him. Some of that was attributable to the
difference in transmit antennas. Adrian had a shortened (but very
efficient) single element vertical while I was running a full size four
square of Rohn 45 sitting on miles of copper. However, accounting for
the differences, Adrian nevertheless clearly heard better. . .many times
a lot better. He was hearing me consistently Q5 at times when I could
hardly tell he was even there. I was a bit frustrated as I had always
"heard" very well at my old QTH. At that point Adrian began mentioning
on KST chat something about a "CW speaker" which made possible his
excellent receive capability. Along about the same time N4IS/JC was
mentioning something about a similar speaker, singing its praises.
Clearly, something was afoot. Adrian and JC both explained their unique
but effective approaches to the CW speaker. Being an acoustical and not
an electronic device JC's approach used PVC tubing for the acoustically
resonant element while Adrian's approach used small square metal
tubing. Both devices use a small speaker driving an acoustical chamber
which is coupled with acoustically resonant tubing. Obviously both
construction approaches, while somewhat different, were very effective
and worked well. At that point I approached Adrian about building me a
unit. He did and a couple of months later the unit arrived in Iowa from
Australia in good condition being very carefully and substantially
packed. Upon inspection Adrian's CW speaker was impressive. . .compact
and beautifully constructed of very high quality materials. I quickly
unpacked it and got it installed. I used the "Line Out" audio on the
Flex Maestro console for an audio source and a small power supply for
the internal amplifier. The unit has a switch for traditional "straight
through" broad band audio and a position for "narrow" audio.
After hooking up the unit I was excited to see how it performed.
However, I was quickly disappointed with the results. I could see no
improvement whatsoever in the ability to copy weak CW signals. I was
stumped and a little disappointed. Adrian had supplied a carefully
measured audio frequency response graph which showed a significant
improvement (about 20 db!) in S/N at my chosen frequency of 610 Hz. I
have tried various combinations of RX and TX antennas, different
bandwidth settings on the Maestro but to no avail. The CW speaker's
performance simply wasn't matching up with neither Adrian's nor JC's
observations of truly significant improvement in the ability to
literally pull weak CW signals out of the noise. My unit simply didn't
do that. I disconnected the unit and put it on my bench (with modest
test equipment) and did a simple audio frequency scan with an audio
oscillator to see the response. The unit had a very large and sharp
(about 10 or 15 Hz bandwidth) audio response in the "narrow" position.
I reinstalled the unit for further testing and evaluation thinking I
must be missing something. After several weeks I finally approached
Adrian to tell him I saw no improvement. I was hesitant and cautious as
I know Adrian and JC are both quite technically competent, credible, and
would not be making unsubstantiated claims. After much thought and
further off line discussion with Adrian I believe we have resolved the
mystery. Adrian is running an analog receiver while I am running an SDR
receiver (Flex). It appears that the SDR receiver will not provide
recoverable audio below the real time receiver noise floor threshold
while the analog receiver can. The real explanation is probably more
complex than that but that's the essence of our observations. That said,
I think it's spot on.
It's entirely possible I may have missed something here along the way.
That said, from my perspective, don't expect a miracle from a "CW
speaker" if you're using an SDR receiver. . .YMMV.
73 from Iowa. . . Dave, W0FLS
2025-11-04 16.51.11.jpg
Description: JPEG image
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
|
