Hello gents,
I built such a CW speaker years many years ago, from plans in an amateur
radio magazine (CQ?, probably published around 1960).
It was tunable, using a hard plastic piston that manually slid up and down
inside a thick cardboard cylinder above (and parallel with) the 3" speaker,
in the much shorter bottom cylinder. The air gap between the two cylinders
was about 1/2".
I never measured the bandwidth curve, but all I can say is that the audio
peak was very sharp indeed.
As sharp as the audio peak was at the resonant frequency of the speaker, I
found that its effectiveness was directly dependent on the bandwidth of the
receiver.
Using an older analog receiver with no IF filter, or just a 2.4 kHz SSB
crystal filter, there was a definite improvement in copyability using the
CW speaker. However, using a good 2:1 200 Hz crystal filter, the speaker
was of little additional value in hearing a very weak Morse signal at or
near the noise level.
An SDR (Software Defined Receiver) employing a good FFT (Fast Fourier
Transform) algorithm beats a CW speaker any day of the week! In such an
advanced receiver, very narrow perfect filters can be created of any
bandwidth, and with no ringing.
73 Mike
W0BTU
On Sat, Feb 7, 2026, 8:07 AM David Raymond <drbp4858@gmail.com> wrote:
>
> 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.
>
> ...
> 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
> _________________
>
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