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 < [email protected]> 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 > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > -- --w8lvn-- _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
