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If
you ask owners of
the same radios how
the radio works you
can get a wide range
of answers. We often
find owners don’t
notice a radio
performs poorly
compared to other
radios even when the
radio has known
major defects or
shortcomings.
This is why we have
to be very careful
asking opinions
about radios.
Why the Difference
in Opinion?
Sometimes we become
emotionally attached
to our toys. After
all, we invest time
and money in our
hobby. We have a
right to enjoy what
we worked for.
Sometimes the
attachment or
emotions greatly
affect our opinions.
I
remember the first
brand new radio I ever
bought.
After years of home
brewing or buying
second or third hand
gear I finally was
in a position where
I could afford a
brand new high end
radio. I carefully
asked all the right
questions and heard
all the answers
I was looking for. I
purchased a radio
people I trusted
really liked, and I
took delivery of my very
first brand new
radio. It was an
expensive radio but
I finally was able
to buy my first top
of the line new
radio.
I
loved the large
digital readout. The
receiver sounded
great. People gave
me glowing reports;
they all said the transmitted
audio sounded
wonderful. Then the
second or third day
came along…..
After a few days of
SSB ragchews and
barefoot CW
contacts I finally
listened for some
weak CW DX. My local
noise floor is way
down near S1, even
on 160 meters, so
DXing should be a
real pleasure with
such a fancy radio. I
heard a weak but
easily readable
signal in the area
where DX normally
hangs out, i
expected it to be
European DX. I was
shocked to hear it
was VE1ZZ. I
wondered why Jack
was only S-3 instead
of his normal S-9 +
signal. I tuned
up the band a little
higher in frequency, and there was
Jack VE1ZZ again but this
time his normal S-9
signal strength!
Puzzled by this and
wondering of Jack
had a problem, I
did my customary
crosscheck. I used a
totally different
type of radio to
look for the same
spurious signal. The second weak
signal from Jack
wasn’t there at all
on my old IC-751A!
It wasn’t there on
an old R4C Drake
either. Obviously
the new expensive
receiver had some
spurious responses,
even on a signal
from a few thousand
miles away!
I tried
transmitting using
that rig with my
full-power amplifier. It
was a single 8877
with 4000 volts on
the anode. This
required reducing
the power output of
my 150 watt radio to
about 50 watts. I
reduced the power,
loaded up, and was
all set to transmit.
As soon as I touched
the key the
amplifier tripped
right off. It gave
me a “grid current
overload” fault. How
could that be? I
loaded up to only
25mA of grid
current.
I
advanced the loading
control on the
amplifier and hit
the key again. Now
the amplifier dumped
because of an SWR
fault.
Out to the shop I
went, new radio in
my arms. I quickly
discovered the
receiver would
actually hear
signals on an
unselected VFO when
the unselected VFO
and active VFO were
close in frequency!
While this spurious
response was 50 or
more dB down
(depending on VFO
spacing), it was
enough to cause
spurious signal
responses on a VE1 a
few thousand miles
away on 160 meters!
This was not good.
Making matters even
worse, the
transmitter had the
same spurious
response. I could
generate, with the
right VFO spacing,
weak spurious signals
spaced at the VFO
separation of and
also on
both VFO
frequencies.
I looked at the
transmitter power
and my mood suddenly
worsened. I
discovered the
transmitter, on a
good peak detecting
meter I used for
pulsed transmitter
measurements, had a
leading edge power
spike of 250 watts
or more! Worse yet
it had this same
power spike when the
power control was
reduced to 50 watts.
No wonder it was
tripping the very
fast fault detection
circuits in my
amplifier.
A
call to the
manufacturer
revealed they
actually knew
about these issues.
They said I was
stuck with the power
spike, but the
receiver and
transmitter spurious
responses were
caused by leakage
through a solid
state switch that
selected or
deselected the
unused VCO’s. They
could cure the
spurious signal
problems by making
a factory modification
to completely
turn off unused VCO’s (the
front panel calls
them VFO’s) if I was
willing to give up
QSK operation.
Why didn’t others
notice the problems?
If we
have a noisy
location, work only
strong signals on
SSB, have small
antennas, and run
low power almost any
radio will be good
enough.
The better our
location, the better
our antennas, the
more power we run,
the narrower the
selectivity we use, and the more we
operate congested
bands the more
important radio
performance becomes. When I was in strong
SSB ragchews, when I
wasn’t working split
frequency, and when
I didn’t have the
low-drive amplifier
with fast protection
circuits on,
everything looked
great. I would have
told anyone who
asked to buy that
radio, just as my
friends told me.
My
friends mostly work
SSB and don’t have
particularly quiet
locations or big
antennas, and
those were the
people I relied on
for advice. If I
never worked weak
signal DX from a
quiet location,
never operated close
to other people,
didn’t work much CW,
and didn’t have a
fast protection
system in my
amplifier I probably
would not have
noticed the serious
flaws in that $3000
dollar radio. If i
only worked SSB i
would have thought
anyone finding fault
with that radio was
crazy.
What’s important to
you?
As humans with
emotions, we all make some
pretty stupid
subjective claims
from time to time.
I’ve seen people
claim an $8000
radio with a
close-spaced signal
dynamic range defect
is bothered by other
signals because it
“hears better, and
so it hears the
defective signals
where other lesser
receivers will not”.
Others will claim
they changed
receivers and
suddenly HF noise was
greatly reduced.
Unfortunately these
statements are
actual technical rubbish.
Virtually
any radio today has
plenty of
sensitivity.
Virtually every
radio made in the
last 20-30 years
will “hear” way down
into ambient noise
at the quietest
location when on a
reasonable antenna,
even when the
antenna is just an
ordinary old dipole.
For many years
internal receiver
noise has not set
the limit of hearing
weak signals, the
external noise sets
the weak signal
limit. For
the same general
filter selectivity
on a clear band,
virtually all radios
produce a
signal-to-noise
ratio determined
solely by the
signal-to-noise
ratio at the
antenna.
What sometimes fools
us is AGC
slope at low levels
or the overall
receiver gain. If one
receiver has a bit
less sensitivity
than another and we
listen to fair
signals, the lower
gain receiver (or a
receiver with less
AGC loop gain) will
provide an illusion
that background
noise has decreased. This
illusion occurs
because receiver gain
between signal
amplitude peaks is
not nearly so high.
The receiver does
not reject or remove
noise, the
background noise
between signal peaks
just doesn’t pump up
so high. Years ago
receivers had an RF
gain control that
was used just for
this purpose, to
reduce sensitivity
and make a signal
sound clearer. Today
the receiver RF gain
control virtually
NEVER controls the
RF gain!! In the
modern rig the RF
gain control is
generally a
mislabeled or
incorrectly named IF
gain control. Today,
in nearly all cases,
the only way to
reduce RF gain is to
turn off the
receiver’s
preamp or add an
attenuator pad.
What is the
difference between
rigs?
Other
than bells and
whistles 99% of us
never use and
transmitter power
output, the only
consistent
benchmarks are the
bandwidth
performance of both the
receiver and the
transmitter.
When
we buy a less
expensive “does
everything radio”,
like a compact
portable or mobile
rig, we generally
get the worse end of
modern transmitter
and receiver
bandwidth
performance range.
Strong
close-frequency
stations, even when
they have no
transmitter defects,
will bother the
receiver. The
transmitter will
also bother others
much more than
necessary when we
are strong.
Filtering is also
important. A
few radios totally
omit conventional
analog IF filters,
depending
exclusively on DSP
filters. “DSP
processing only”
receivers, whether
$800 or $8000 rigs,
almost always
provide
significantly poorer
close-spaced
performance than
similar radios using
conventional crystal
or mechanical IF
filters. The best
receivers combine
very narrow
selectable roofing
filters tailored for
each mode with a
good DSP or standard
filtered IF and
detector stages. The
Ten-Tec Orion or
Elecraft K3 have two
of the very best
receivers, far
better than much
more expensive
radios.
It’s important to
keep in mind if
we never operate
close to other
strong signals, if
we have high local
noise, if we use
small antennas
and/or low power,
and if we operate
wide bandwidth modes
we aren’t nearly as
likely to appreciate
good quality.
ARRL reviews have
now improved. The
ARRL now tests and
reports performance
at closer spacing.
It is worth looking
at ARRL reviews,
especially at
close-spaced IM3
dynamic range and
transmitter IM
distortion. ARRL
numbers are more
useful now, although
review text
sometimes has the
same unreliable
emotional hyperbole
we find on the air.
Also look at the
following links on
this site for
receivers
and
transmitters.
since 10 Mar 2007
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