Topband: CW Speaker - follow up

[David Raymond]

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
>
>