What creates CW key clicks?

What_Causes_Clicks?

Bandwidth
rules Part
97.307 

Clicks
are often a problem
on congested bands,
yet with modern
radios they don’t
need to be a
problem. In the
past, engineers and
designers didn’t
have the easy
ability to generate
filtered waveforms.
Radios lacked wide
2-3 kHz wide SSB
filters, let alone
narrow 250-500Hz
filters. Op-amps
were unheard of, and
L-C filters were
large, bulky and
expensive. Today,
every radio
manufactured has the
ability to be very
clean. 

Modern
Radios

Most
modern radios
include 500Hz and
narrower receiver
filters that operate
at the same IF
frequency as their
transmitter section.
Transmitted signals
are often routed
through the SSB
filters with
intentional TX
switching, when they
could just as easily
be routed through CW
filters! We will see
later in this page
that TX signals
could be routed
through CW filters
to eliminate
sidebands, yet
manufacturers
foolishly use the
SSB filters. If you
examine the
bandwidth of a
FT1000-series radio,
you will find the
clicks disappear at
the BW limits of the
SSB filter. This is
because they run an
essentially unshaped
CW signal through
the SSB filter, and
that filter sets the
bandwidth of clicks.

The
sad thing is once
you listen to that
signal through a
500Hz filter, it
sounds absolutely no
different ON
FREQUENCY
than it would if it
were nearly click
free. The only
people who can
notice the
difference between a
clicking rig and a
clean rig are the
people operating on
adjacent
frequencies! Claims
that certain shapes
produce certain
“bell
sounds” or high
readability are not
correct, they are
certainly not based
on engineering or
actual blind A-B
tests. 

If
you examine the
audio output of your
radio with a 500Hz
filter in use, you
will see ANY
waveshape
transmitter has the
same nearly
raised-sine (Gauss
or Bell curve)
shape output to your
ear! That includes
wide signals and
narrow ones. The
speed limit you can
copy with a 500Hz
filter is the same
limit you can
transmit with. It
makes no difference
what end of the path
the filter is on, or
if there is one at
both ends, so far as
speed is concerned!
(This assumes the
filters have
reasonably good and
easy to achieve
group-delay
characteristics.) We
hear a few mS rise,
no matter if it is a
sine shape or a
square, as a
“tick”.
For demonstration,
listen to the pure
sine wave on WWV
that
“tics”
every
second!       

What
Could Be Done

At
no cost to
manufacturers, they
could build a click
free radio. Every
component is in the
radio, the problem
all centers around
poor or careless
engineering. 

Amplifier
stages are
reasonably linear
(so they can amplify
SSB), and virtually
every radio contains
power control
circuitry that could
be easily modified
to provide
wave-shaping. Even
without
wave-shaping, the
transmitter could
process transmitted
CW though a 250Hz or
500Hz filter. 

Sadly,
most of the commonly
used radios have as
bad or worse keying
characteristics than
old rigs. It’s as if
the manufactures
either don’t
understand CW, or
don’t care. The
result is we are
left with a mess,
because many
top-of-the-line and
very popular rigs
have horrible keying
sidebands. 

On
frequency with
normal CW filters,
we would not be able
to tell any
difference between
the sound of a
clicking radio and
one that is clean!
There is no
justification or
reason for radios to
be 3kHz wide on CW.

How
to Identify Click
Problems             

We
hardly notice
clicks, and we
certainly can not
tell a clean rig
from a dirty rig,
when we are
listening right on
the CW station’s
frequency! Even an
scope won’t tell us
much about signal
bandwidth, or if the
rig has excessive
clicks.

In
order to check
clicks, we must:

1. Be
   sure the
   receiver is not
   overloading

2. Listen
   with the CW
   signal outside
   the receiver
   filter’s
   bandwidth

3. Listen
   when the noise
   is low, and the
   signal
   reasonably
   strong 

If
we do not follow
those three
guidelines, we can’t
tell if a rig is
clean or
not. If you are
testing your own
rig, your second
receiver must have a
narrow filter and be
coupled to the 
rig-under-test
through a proper
attenuator.   

Why
Worry About Clicks?

Clicks
are most problematic
when we try to copy
weak signals next to
moderately strong
signals. If you only
operate on empty
bands, run low
power, and never
operate within four
or five kHz of weak
stations, bandwidth
is probably not a
concern. 

If
we contest, work DX,
or Ragchew near
other QSO’s, and
especially when we
run more than a few
hundred watts and
have large antennas,
we should be mindful
of our bandwidth. If
you listen to a recording
of a clicking radio,
you can hear how
devastating clicks
are to nearby weaker
signals. This
signal is from
Europe on 40 meters,
and it is daylight
over half of the
path!! 

For
a mathematical
tutorial on clicks,
visit W9CF’s
site. Kevin’s
analysis deals with
bandwidth
requirements related
ONLY to modulation
of the envelope.
I’ll explain the
same thing in verbal
form, as I discuss
sidebands created by
rise and fall times.
CW keying is really
just 100% AM
modulation, as you
will
see!    

There
are several
INCORRECT but
popular
misconceptions. They
are:

What
Causes Clicks?

While
a fast rise and fall
time guarantee
excessive bandwidth,
a long rise
and fall is no
guarantee a radio
will be
“click-free”.
Some radios switch
into transmit while
the synthesizer
(VCO) circuits are
still settling to a
new frequency. An
IC-775DSP I owned
was particularly bad
about this, and also
had VCO leakage
problems. The amount
of garbage varied
with how I used the
radio, including
“VFO”
frequency settings
of unused
VFO’s! 

Radios
with VCO or
synthesizer settling
time problems
generally produce a
loud
“thump” on
key closure on the
second VCO
frequency. That
thump will be right
on the DX station
when the operator is
working split. If
you listen in
pileups, you will
hear a small
percentage of rigs
with this problem.
If the operator uses
QSK,
VCO-switching-thumps
can be particularly
annoying. Thumps
will occur every
time the VCO moves
from the receive
frequency to the
transmit frequency,
sounding like a
leading-edge
click! 

Rise
and fall times are
also important. A
long rise and fall
time does not always
result in narrow CW
transmitter
bandwidth, even
though a
faster-than-needed
rise and fall time
almost certainly
results in excessive
bandwidth.
Many radios have
rise and fall times
that are much too
fast.

How
fast is much too
fast? For now let’s
ignore VCO switching
problems, and
consider envelope
shape. 

Rise
and Fall

The
ARRL recommends a 5
mS rise and 5 mS
fall time for CW,
based on data in
section 2.202 of FCC
rules and CCIR Radio
regulations.
According to
professional
sources, a 5 ms rise
and fall time is not
harmful to
readability at 35
wpm under marginal
(fading) conditions,
and 60 wpm when
signals are
reasonably above
noise floor. This
rise and fall
results in a
occupied bandwidth
of 150 Hz, although
unwanted transient
energy caused by the
shape of the
waveform slope may
appear at wider
bandwidths. 

What
Limits Bandwidth?

When
determining
bandwidth of a
stable signal (no
oscillator
problems), two
things come into
play in.

The
slope (bandwidth)
and the amount of
change in a sloped
area (level) combine
to determine how
offensive the
transmitted signal
is. Very
subtle changes in
envelope shape have
a profound effect on
key click amplitude
and frequency
dispersion. This
makes it nearly
impossible to tell
if our radios are as
clean as they could
be by looking at
envelope
shape. 

We
can be certain sharp
transitions will
cause problems,
especially if we can
actually see them on
a oscilloscope. We
can also be sure
that a rise and fall
faster than 2 or 3
milliseconds will
cause a bandwidth
problem. 
 

Reference
Data for Radio
Engineers, in the
section of Radio
Noise and
Interference,
addresses key clicks
in a manner the ARRL
Handbook does not.
They give an example
of multi-pole
shaping of
waveform. The
ARRL Handbook seems
stuck with the
incorrect notion
that a single-pole
R/C filter provides
proper shaping,
something doubtless
left over from
1940’s technology
when better filters
were expensive,
large, and
complicated.

Here
are the bandwidth
curves of three
basic envelope
shapes, one
rectangular (some
radios are this
bad!), one for a
proper single pole
R/C filter with
slightly rounded
shape (The ARRL
suggests this shape.
Probably because it
was practical in the
early years and
“stuck”
even though it is
not ideal), and one
for a filtered rise
and fall (this would
be a sine-shaped
rise and fall from a
multi-pole filter).
We can clearly see a
large difference in
bandwidth in the
curves
below:      

From
Ref Data for Radio
Engineers 29-10 1977
Edition

Most 
radios, through poor
design, fit in the
rectangular to
slightly-rounded
category!

How
Can I Fix My Radio?

Some
radios are easy to
cure because others
have done the work
for you. If you are
looking for a cure
for a unique radio
you first have to
understand exactly
how the keying
system in your radio
functions. To
have a clean signal,
the following
processes must occur
in exact order:

1. The
   oscillators must
   move to the
   transmit
   frequency and
   become totally
   stable.

2. The
   antenna and
   amplifier have
   to be fully
   connected and
   ready to amplify
   in a perfectly
   linear manner.

3. The
   transmitter’s
   stages must be
   ready to
   amplify, but
   must be held off
   by gain
   reduction.

4. The
   gain or power
   output of the
   entire
   transmitter
   system must
   increase with a
   waveshape that
   has low harmonic
   content (it
   can’t have sharp
   edges). The
   slope or time of
   the rise must
   take enough time
   (3-5
   milliseconds) so
   first order
   sidebands aren’t
   extending out
   too far. It is
   actually an AM
   transmitter at
   this point!!

5. The
   envelope must be
   somewhat stable
   in level until
   the key is
   released.

6. The
   falling edge has
   to be bell
   (gauss curve) or
   raised sine
   shaped with a
   period of 3-5
   mS.

7. After
   RF reaches zero,
   the transmitter
   circuits can be
   shut off.

8. The
   amplifier is
   placed in
   standby.

9. The
   antenna switched
   to the receiver.

Tracking
all this down is
lengthy, and
requires a dual
trace scope and
“dit”
generator.

Things
that can 
prevent this are:

1. ALC
   tends to sharpen
   the leading edge
   and roll it over
   too fast at the
   top.

2. Keying
   control rise
   waveform. Most
   system filter
   only with a
   simple R/C
   filter so
   harmonics are
   rich

3. VCO
   or VFO switching
   time issues.
   Some radios go
   into the
   transmit mode
   before the
   synthesizer or
   VFO is fully
   stable.

4. Amplifiers.
   Some amplifiers
   are still
   switching or are
   not biased on
   when the
   transmitting
   envelope starts.

What
Can Manufacturers
Do?

Radio
manufacturers can
certainly do a great
deal more than they
are. First, they
created the problems
through poor
engineering and
design. Why are we
stuck fixing them?
Did they take our
money and run? 

All
of the parts are
there to make radios
virtually
click-free, yet the
only manufacturer
who has taken an
active interest in
this (and who seems
to care at all about
our signal quality
and frequency usage)
is Ten-Tec! To date
I haven’t found any
other manufacturer
admitting a problem,
or even offering
technical support
for bandwidth
problems. 

Let
me give an example
of what could be
done with current
radios:

Virtually
every radio contains
a CW filter that
operates at the IF
frequency of the
transmitter, yet
nearly every radio
transmits CW through
the SSB filter!
Engineers actually added
circuitry and parts,
in many cases, to
steer the CW through
the wider filter on
transmit! If
you listen to
radios, in
particular the
FT1000-series, you
will notice they
have an ultimate
click-bandwidth of
about the same width
as the SSB filter.
That’s because the
poorly-shaped CW
waveform with
excessively fast
rise-and-fall is
filtered through the
SSB filter.

If
these same radios
immediately turned
on the output
stages, and held
them on for several
mS after the key
line was opened,
they could send
perfect filtered CW
through the CW
filter. A 500Hz
filter would cause a
steep roll-off in
clicks, even if
driven by a
relatively
“square”
and very broad CW
signal. The
resulting waveform
would be a slightly
modified raised-sine
envelope.  

The
listener would not
be able to tell any
difference
between the ON
FREQUENCY sound of a
500Hz CW-filtered
transmitter and an
unfiltered signal
with excessive
bandwidth, if he
used a 500Hz or
narrower filter in
his receiver! As
a matter of fact, I
normally transmit
through a 250Hz
filter in my
FT1000D, rather than
the 2.4kHz SSB
filter Yaesu
selected. No one
listening on
frequency, even DX
stations copying my
signal near noise
level, can tell the
difference when I
select 2.4KHz or
250Hz bandwidth! The
only place
transmitter
filtering makes a
difference is up or
down the band from
my operating
frequency. 

This
is why we can not
tell whether a
signal has a proper
rise and fall time,
sharp level
transitions, or any
other envelope shape
problem when we
listen to the actual
CW tones through a
500Hz filter. 
Even a very fast
rise-time, with a
spiked rise and
fall, sounds good
(and even looks
perfect on a scope
connected after the
receiver’s narrow
filter)! 

 Claim’s
that a certain shape
rise and fall
produce a
“pleasing-sound”
are not true at all.
First, our ears
can’t identify a
sound only 5mS long,
and second…the
receiver’s CW filter
(assuming it is
under several
hundred Hz BW)
reshapes the
waveform to a proper
rise and fall! 

Why
is any of this our
concern? Why do we
have to work on
radios, and suffer
with clicks?
Certainly not
because of a cost
issue! All the parts
are in the radios.
It is a simple lack
of good
design-engineering,
most likely driven
by a lack of concern
by manufacturers for
providing rigs with
good signal quality.

What
Can We Do?

First,
we can let
manufacturers know
it is their
problem.
Let’s ask the ARRL
to publish useful
reviews with
bandwidth pictures
showing a spectral
display of CW (and
SSB) bandwidth.
Let’s ask them to
check for VCO
problems, and
publish any
abnormalities. Let’s
rate radios as poor,
fair, good, or
excellent so readers
don’t have to be
EE’s to understand
what they are buying
(and using).

Radios
are too expensive,
too difficult to
work on, and last
too long for us to
ignore this problem.
We need to stop
these problems at
the design phase,
instead of out in
the field.