I should also mention the other CW speaker user is operating local with
a direct connection to his K4D.
73. . . Dave, W0FLS
On 2/11/2026 11:01 AM, David Raymond wrote:
Greetings Topbanders. . .
My original post of February 7 has started a lot of discussion. . .
some of it remarkably thoughtful and insightful. The aggregate
knowledge on this reflector is nothing short of amazing.
A quick recap. . .my original post detailed my experience with
Adrian/VK2WF consistently copying my 160m CW signals consistently
better than I copy his (see original post). I'm operating the Flex
remote via a Maestro using a nearby station. Having had dozens of
morning QSOs with VK2WF and compensating for the difference of ERP I
was perplexed how Adrian was consistently copying my signal fairly
well when I had a hard time even telling he was there (both of us have
low noise levels). At some point a little later Adrian told me about
his "CW speaker" and what a difference it made in literally pulling
signals out of the noise. He mentioned that he could listen to his
receiver with the CW speaker in the "Wide" (pass through) mode and my
signal would be uncopyable, sometimes even undetectable. He could
then flip the switch to "Narrow" and my signal would be Q4 or better.
After suffering through many mornings with Adrian hearing me clearly
better than I was hearing him I asked him if he would build me a CW
speaker which he did. To cut to the chase it arrived and I got it
quickly hooked up to the Maestro using the "Line Out" audio.
I began listening and was immediately disappointed. Clearly I wasn't
seeing the "magic" that Adrian was. I could listen on the CW speaker
in the "Wide" mode and, having the Flex bandwidth set for 3 or 4 kHz
and APF "off," I had normal receive audio as expected . . . more
noise, close in signals causing QRM as usual. When I switched the
speaker to "Narrow" with the receiver widened out the audio noise
floor dropped significantly and already copyable CW signals were well
above the very low audio noise floor (but S/N essentially the same
copy as using the narrow filtering in the rig). In this configuration
I could not copy signals that were at or below the receiver noise
floor. I then returned the Flex to my usual CW setting of 250 Hz
bandwidth and fair amount of APF dialed in (probably 50 or 75 Hz of
audio bandwidth) I could go from "Wide" to "Narrow" with
_no_ apparent improvement in S/N or copyability. I finally put the CW
speaker on the bench testing with an audio oscillator with it showing
an extremely sharp peak at the audio frequency of 610 Hz (my desired
listening frequency) as expected with a very narrow response (maybe
about 15 Hz). The speaker was doing exactly what it was supposed to
do. I was stumped as to why no improvement on extremely weak signals
that Adrian was seeing on his end.
In the meantime, another faithful Topbander had procured a CW speaker
from N4IS to be used with his Elecraft K4D. In conversing with him he
confirmed he was having basically identical results with his CW
speaker. . .no copy improvement signals beyond normal narrow filtering
from the rig and nothing from the CW speaker once the signals dropped
below the receiver noise floor. After discussion and comparing notes
further with Adrian we finally concluded that the difference seemed to
be based on the fact that my receiver was an SDR while Adrian's was a
home brew analog receiver (and rather elegant). The other CW speaker
user related an identical experience. Based on the two CW speaker
examples we concluded that the difference in copyability between
Adrian and me (and the other user) occurred when incoming signal
levels slipped below the SDR receiver noise floor making the signals
no longer recoverable while signals below the noise floor on Adrian's
analog receiver _were_ recoverable.
The response to my original post has been a bit overwhelming including
many sent directly to me and some phone calls. I will attempt to
summarize what I've learned from the input I've received as follows:
1. In essence, it seems that once the signal slips below the SDR
noise floor it is essentially "lost." While it may exist in there
somewhere it is unrecoverable with current SDR capability in amateur rigs.
2. The loss of recoverable audio could be attributed to many things
in the A-D/D-A conversion processes. . .sampling rate, dynamic range,
phase noise, quantization errors, etc.
3. All of this could be further compounded by the fact that I'm
operating remote. . . adding in all kinds of unknown processes
occurring in the circuitous digital path on the internet between my
home (with the Maestro and CW speaker) and the remote site (with the
Flex).
4. At least two people suggested the use of a low noise preamp at the
beverage to raise the overall composite RF signal level at the
receiver available for processing (acknowledging that S/N would
remain the same) giving the A-D converter a better chance of
recovering the weak signal bits from the low composite RF signal level
(we have a 20 db low noise switchable preamp at the bev remote
switching point made no change).
5. I will take the CW speaker up to the remote site and hook it up
directly to the Flex removing both the Maestro and the internet path
from the equation to see if that makes any difference.
As I said previously, I could easily be missing something here along
the way. . .I'm an old analog guy and far from a DSP expert. If
anyone has further ideas to share or suggestions for things to try
please feel free to respond directly to me if you wish. I will share
anything significant I learn or any new developments here on the
reflector.
73. . . Dave, W0FLS
Here's a photo of the VK2WF CW speaker:
https://www.dropbox.com/scl/fi/kbddxg0lj1jb260bfr6je/2025-11-04-16.51.11.jpg?rlkey=cya2nnfnljbg3j98lju7bgyto&st=bdpq8qjl&dl=0
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