Hello Steve:
They are probably not "key clicks". Watch your S-meter as you tune away and
you'll likely notice the tone disappear while the meter still shows the
signal at or near maximum strength!
The K3 has two levels of filtering at two different places in the receiver's
signal path. The first is the so-called "roofing" filter at the first
intermediate frequency (I.F.). That's the crystal filter currently selected
and shown on the display below "X-FIL". Then, after passing through that
filter and being amplified, the signal is converted to the second I.F. where
additional filtering is applied, this time by means of the Digital Signal
Processing (DSP) circuits.
The DSP filtering is continuously variable with the WIDTH control and,
normally, the WIDTH control automatically selects the appropriate X-FIL for
the bandwidth you are using.
Tune off to the side of a signal so the tone disappears but you can still
hear the keying while the S-meter is still displaying a strong signal, now
slowly reduce the WIDTH control for a narrower bandwidth. In almost all
cases you'll hear the clicks stop.
That's a sure sign the clicks were not being transmitted, but are really
just an artifact created by having the signal within one edge of the K3's
first I.F. bandpass while the DSP bandpass was too narrow for you to hear
the tone. If the clicks were coming from the transmitter, you'd still be
able to hear them no matter how narrow the bandwidth because they would be
present over a wide range of frequencies above and below the transmitter's
carrier.
If the clicks are still audible at minimum bandwidth, they are likely being
transmitted.
Of course some "clicks" are inherent in CW. You can't key the carrier
without producing "clicks". They are just sidebands produced by modulating
(keying, in this case) the carrier, like any double-sideband amplitude
modulation. In an advanced rig like the K3, the shape of the keying waveform
is carefully set to minimize them, but they are *always* there if you look
closely enough and their distance from the carrier will vary with the keying
speed.
If your receiver bandwidth is too narrow the effect will be to "soften" the
keying and make it harder to copy. In the extreme a very narrow bandwidth of
a few Hz would make a keyed signal sound like it wasn't keyed at all.
The practical minimum bandwidth for good copy is about 50 Hz (0.05 kHz on
your K3 display) and that's as narrow as you can go with the K3. That will
provide decent copy by passing the essential sidebands (clicks) at typical
CW speeds although very high speed operators will find better copy at wider
bandwidths.
Many older rigs do produce wider sidebands (clicks), much to the vexation of
some of the high-density pileup and contest specialists. How wide is "too
wide" depends on the transmitter since anything newer than a spark
transmitter is perfectly legal on the Amateur bands. Over the years I've
often read that clicks should not be heard beyond 500 Hz or so on either
side of the carrier, even on antique rigs. And, of course, their level is
well down from the signal strength itself.
Nowadays we're seeing more wide band clicks out to several KHz than we did
for a number of decades in the past. That is, as you note, probably to
people over-driving amplifiers thinking they don't need "linear" operation
for CW. Linear operation is essential to preserve the keying waveform. (In
old rigs, we keyed the final amplifier directly so it did not need to be
linear just as we modulated non-linear - Class C typically - amplifiers to
produce clean double-sideband AM phone.)
The "splatter" you hear on SSB is much the same, only in that case it *is*
RF being transmitted some distance from the carrier signal - typically up to
almost 3 kHz from the carrier on the side band being used. If you tune
across it with a narrow filter you'll hear the bursts of RF power
corresponding to the modulation at that frequency that occur in your
bandpass. And we do have those Hams who think more is better ("all knobs to
the right") who push their SSB rigs beyond their specified maximum power or
who drive external amps too hard.
Phase noise is just like the hissing, normal band noise. It, too, is just
modulation on the transmitted signal and will typically fall off rapidly as
you tune away from the carrier. If the signal is CW, you can hear it being
keyed.
73,
Ron AC7AC
-----Original Message-----
From: elecraft-boun...@mailman.qth.net
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Steve Walter WA3A
Sent: Sunday, November 01, 2009 12:59 PM
To: elecraft@mailman.qth.net
Subject: [Elecraft] K3 CW Reception
Now that I have my first receiver that actually hears whats on the band (K3
of course) I am in need of some education on cw reception. I have K3 #3397
with 2.7, 1.8 and 400 hz filters. Latest beta.
When tuning away from a cw signal and the tone disappears I continue to hear
clicking (not quite clicking but more like cw with no tone) for up to
another 500 hz. Usually more like 250-300 hz. I normally use the 400 hz
filter. Reducing rx bandwidth begins to help around 100 hz but its still
noticeable. I believe this is caused by the transmitted cw waveform and the
rise and fall times. My understanding is that this is also what causes key
clicks but I'm not sure if thats what I'm hearing. To me, key clicks would
extend further from the center than what I'm hearing. Is this what also
causes faster cw to use more bandwidth? It is on all cw signals and not
related to strength (although its usually wider with a stronger signal) or
AGC settings (including off). Of course, on steady carriers I dont hear
anything once the tone is gone. When listening to a TS570 its not nearly as
noticeable BUT there are alot of other things going on like AGC pumping and
images and just mushy audio in general. Its amazing to me how bad the 570
sounds after using the K3.
Another part to this question: What does transmitted phase noise sound like
on reception? I have read a lot of posts on phase noise but I have no idea
what people are hearing.
And maybe on a related topic I have also noticed SSB splatter much more with
the K3. Is this also related to the K3 just being a cleaner receiver?
None of these issues seem to be rx overload. I dont use NB, NR and always
use the ATT on the lower bands. As I said before I have tried various AGC
settings including agc off and backing off the rf gain with no real
difference.
Maybe I'm just now realizing what alot of you have been talking about...
Poorly designed and/or improperly operated transmitters/amplifiers. If
thats the case its an eye(ear)-opener for me!
73, Steve WA3A
--
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http://n2.nabble.com/K3-CW-Reception-tp3928524p3928524.html
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