On 7/27/2014 12:54 AM, K8JHR wrote:
I was encouraged by ARRL Lab expert Bob Allison, who reviewed the
same graphs and said,
"THEY HAVE NEARLY THE SAME COMPOSITE NOISE."
Several points. Mr. Allison is probably not a contester. He is looking
as a lab tech, not as a user.
Second, they way the data are plotted with all the data at the bottom of
the graph, it IS hard to see the differences. But when you look at the
data with a reasonable scale, and plot multiple competing radios on the
same graph, the differences jump out at you.
Third, I look at this data from the perspective of someone who must
coexist with all of that noise produced by near neighbors, and others
with strong signals with crummy radios.
My plot of Bob's data clearly shows the Eagle to be, on average, 5-6 dB
cleaner than a TS590, depending on how far off frequency you are
listening. 6 dB is an S-unit, and it corresponds to 4X the transmitted
noise power. That sure matters to me if I'm trying to copy a weak signal
buried by someone else's sideband trash!
James, as part of this discussion, I and others have on several
occasions, observed that the interference between radios consists of
multiple components, most of which are the result of how the radio is
built. They are designed in characteristics, the result design decisions
made by the engineering team to build a product for a defined set of
functions and cost. That's what engineering is! Rick posted an email
from N6KR that addressed some of the design decisions he made in
designing the K3 and KX3 to make both their TX and RX as clean as possible.
Those mechanisms include, but are not limited to, (see, I can get
lawyerly if I wanna) phase noise in the RX, distortion in the RX
(measured as intermod -- IMD), and fundamental overload (the interfering
signal drives the RX to its voltage limits); phase noise and distortion
transmitted by the other station (composite noise in the ARRL tests),
his IMD, his key clicks, and overdrive of his audio. The only one of
these not the fault of the radio's design is the last one -- overdrive
of audio.
What is phase noise? It is a byproduct of the frequency synthesizer
that determines the radio's operating frequency, how much of it is
present depends strongly on its design. Again, see N6KR's email, which
Rick has posted here at least twice. It originally ran on the Elecraft
reflector. Read the ARRL Handbook to learn more.
What is distortion? It is the non-linear behavior of a system (what you
get out of an amplifier is more than a perfect copy of what you put into
it), and the "more" consists of harmonics and sideband trash.
Overdrive of the audio also creates distortion, thus sideband trash.
Overdrive of a power amp also causes its distortion to increase.
ALL amplifiers create SOME distortion (harmonics and sidebands). Study
the ARRL Handbook to understand why. HOW MUCH distortion is produced
depends on the design and how it is driven. How much escapes as
harmonics is determined by bandpass filters, both inside the amplifier
and outside it.
In an earlier post, you made some snide, cheap lawyerly remarks about a
radio that was not clean at rated power and had to be run at lower power
to be clean. The distortion in ALL amplifiers varies with their supply
voltage (close to their design voltage, more supply voltage = cleaner)
and output power. Typical ham amplifiers are cleaner at half power than
at full power. When I use the word "amplifier" here I'm also talking
about the output stage of a ham transceiver.
And don't tell me that we have not tried to teach you. At least a month
ago, I posted a link to an excellent tutorial on the topic by K6XX. It's
still on my website. k9yc.com/publish.htm
73, Jim K9YC
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