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
3-S DCARC 2025 .pdf
Description: Adobe PDF document
CW PITCH STYDY paper 0.pdf
Description: Adobe PDF document
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
|