Is there a way to build analog audio filters that duplicate the effect of
the cw speaker setup?
w8lvn
On Sat, Feb 7, 2026 at 4:41 PM JC(Jose Carlos) via Topband <
topband@contesting.com> wrote:
> Hi guys
>
> Let me share my experience with CW speakers. My first project was built 10
> years ago; I was lucky enough to observe a huge improvement in the ability
> to copy cw weak signal. The center frequency was 350 Hz and since the
> beginning I was using two CW speakers 3 FT apart m, behind my PC monitors.
> Before the CW speakers, I used to see a light trace on the waterfall, but
> not strong enough to copy the signal, after tunning the CW speakers 1 Hz
> apart and 12 Hz bandwidth, I started to copy weak signals even when the
> trace was very light. The signal to noise ratio was better enough to allow
> a
> QSO, I am in a suburban area and using my Horizontal and Vertica Waller
> Flag.
> The CW speaker was very important, and help me to work the last 10
> countries
> to reach 300 CW countries confirmed on 160m, now I am sitting at #305 CW.
> Last year I upgraded my project to a new level, with Q=50. I am using 4
> pairs of speakers now. Center pitch frequency 200 Hz(BW 4 Hz), 300 Hz ( BW
> 6
> Hz), 400 Hz ( 8 Hz) and 600 Hz ( 17 Hz).
> The way to use these devices is important:
> 1- You can use for comfort if the signal is above noise. You can improve
> the
> SNR reducing the QRM, however is a slow process to peak the audio signal,
> example, using my 300 Hz pitch, if I tune the signal 3 Hz off, the signal
> intensity drops 3 db, and it drops 10 db 10 Hz from the center. It is easy
> to tune the signal when the signal is above the noise level.
> 2- When the signal is bellowing noise is difficult to peak the signal, and
> most importantly you only hear the noise and not the signal. The noise on
> TB
> change during the seasons, Summertime the QRN dominate, using a low pitch
> like 200 Hz, it makes easy to copy CW. Wintertime the noise level is very
> low, and 600 Hz works the best.
> I use a splitter after my WF preamplifier and feed the IC7851 and the DDC
> SDR (QS1R), the SDR software HDSDR audio waterfall with VBW 0.3Hz allow me
> to see weak signal you can not hear using 100 Hz BW on the IC7851 receiver.
> After I know that I am in the right frequency, the CW speaker BW can
> improve
> the signal to noise level 10 to 15 db better than the 100 Hz from the
> radio.
> The CW speaker works with the response of a column of air to the
> disturbance
> caused by the speaker, at this point phase noise is a problem, I keep the
> RF
> BW 300-400Hz and sometimes 600 Hz, to keep the noise from the skirt of the
> filter far from the audio peak sides. Some SDR functions does not help to
> keep the phase of the audio at the speaker, Like NB and NR, using them can
> increase the noise you hear from the CW speaker due constant change in the
> phase of audio the signal.
> A pair of CW speaker provide the ability to selective direction, separating
> the noise from the signal is a special acoustic perception. Check 3D sound
> from NASA, attached.
>
> My conclusion is that the CW speaker is a very specific toll to work weak
> signal. It does help when the signal is above noise level but not necessary
> to copy the signal, it is just confort, and it is hard to use for
> contesting. The learning curve to get used to the tuning is also long.
> Without my CW speaks I would not be above 300 on 160m CW.
>
> About the SDR noise floor I disagree, and here is why, I used to record RF
> using HPSDR. I have hundreds of recordings. I can play back the recording
> tuning on the digital segment , 1840 USB and decode signals -24 db using
> WSJT, the weak signal is there, even if I cannot see it on the waterfall. I
> can play back some recordings, like 9M6NA last spring, and do not copy on
> the regular speaker but Q5 on the CW speaker.
>
> My point is that the cw speaker does not work until it works. You need to
> make all the above to hear the results, it is not a plug and play, it is
> very hard to tune. But is very hard to work a new one on 160m, like 10
> years
> ago I worked Heard Is, using my CW speakers and I am planning to do the
> same
> with Bouvet.
>
> Adrian CW speaker works very, very well; both projects use a 1/2 wave tube.
> I am testing different tubes material, my 200 and 300 Hz use aluminum tune
> 1/8 wall. I am testing brass, and Stainless-steel tube.
>
> 73's
> JC
> N4IS
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