Hal Communications CWR6850, Instruction Manual

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CHAPTER 3 PAGE 17
3.4 Receiving Morse Code
Morse Code reception with the CWR6850 requires very little change in switch settings from those
used for RTTY in section 3.2; just change the CW / RTTY to CW from RTTY and retune the receiver
to a CW (Morse code) signal. Refer to the tables in section 3.2 for the rest of the switch settings.
Use USB or LSB for CW reception now and do NOT select the narrow CW filter at this time. Tune
the receiver to the CW segment of the 14 MHz band, 14.000 to 14.080 MHz.
There are two tuning monitors available to indicate correct receiver tuning for Morse reception –
the CW LED on the CWR6850 front panel and audio tone frequency comparison using the internal
audio monitor. The CWR6850 receive circuit is designed to lock onto an 800 Hz tone, so tune your
receiver until the CW LED flashes in sync with the CW signal (key down = tone on = LED on).
When the CWR6850 is receiving CW signals, the filtered and detected Morse data is connected to
both the microprocessor for decoding and to the CW side-tone oscillator. Thus the received CW
signal is regenerated in the CWR6850 and you may listen to the processed signal simply by adjust-
ing the VOLUME slide control. Also, since the CW side-tone is set to 800 Hz, the desired receive
CW tone, you can do a very accurate frequency comparison between the receiver signal and the
regenerated signal by varying the two slide controls INPUT and VOLUME. Try this on a few signals
– you will soon find out that Morse tuning can be very easy.
The CWR6850 includes two internal filtering systems that may be used for reception on Morse
code. The first filter is an active bandpass filter, centered at 800 Hz with a -6 dB bandwidth of 150
Hz. Normally, this is all the filtering you will need to receive Morse code. A second PLL (phase-
locked-loop) filter may be used that has a lock-range of ± 80 Hz, a "bandwidth" similar to that of
the active filter. However, due to the fact the PLL will abruptly cease tracking a signal whose fre-
quency exceeds the tracking range, the effective "skirts" of the CWR6850 with PLL in use are very
steep; the PLL filter will provide any response to a signal frequency beyond its tracking range.
Therefore, tuning a CW signal may be considerably more difficult when the PLL filter is used. The
PLL filter does, however, offer a considerable improvement in received S/N (signal to noise) dis-
crimination and will track the frequency of a drifting CW signal (within the lock range). The PLL fil-
er may give false reproduction in the face of a strong interference since it will lock on the stron-
gest signal within its lock frequency range. On the other hand, the PLL filter may provide a consid-
erable improvement in the "copy" of a weak, noisy signal. The active CW filter stage is always used
for CW reception; the PLL filter may be selected by pressing the SPACE FILTER button in. If a re-
ceiver with a narrow CW filter and passband IF tuning is used, a great number of signal selection
and rejection techniques can be used to isolate your desired receive signal. Tuning indicators that
are used for RTTY are not used in Morse reception; only the CW LED is used for CW tuning,
although you may "match" the incoming signal tone with that of the CWR6850's internal sidetone
monitor as explained above.
After you have mastered tuning of Morse code signal, you may notice that what shows up on the
screen doesn't always make the best of sense at first glance! This is usually due to the fact that
human operators often send imperfect code! When we copy Morse code with our ears and decode
in our brains, we can be adaptive and translate what the sending operator "meant to send" instead
of what actually was sent. The most blatant examples of this are run-together characters and in-
correct spacing between letters an words. It is very easy for the transmitting operator to get in a
hurry and run some letters together - particularly on something he's transmitted often like "CQ" or
his own call. Since we are also good Morse operators who have sent "CQ" and call letters often, we
adapt when receiving by ear and interpret what was intended. The microprocessor, on the other
hand, is looking for some long CW character ( like
–·–·––· – for CQ) that doesn't exist: it therefore
displays the underline character ( _ ) to show that an unintelligible Morse combination has been
received. The CWR6850 SPACE NARROW button may be depressed in such a case to attempt to
recover the run-together code. When SPACE NARROW is used, the basis for judging character and
word space is shorted to 1½ dot units, rather than 3. This feature may improve the "copy" of hand