I was responding to the comment that you "thoughtfully" deleted so you could go
on with your critique.
I know it's hard for some people to believe, but some of us in the unwashed
masses are actually capable of deciding what is "useful" to us in our own
situations.
.
On 9/15/2015 9:50 AM, Jim Brown wrote:
On Tue,9/15/2015 7:10 AM, Wes (N7WS) wrote:
Seems to me that he's just trying to explain himself.
Yes, but in doing so, he's making it clear that his work does not contribute
useful information to a ham trying to evaluate the relative performance of
radios in a strong signal environment, AND that's what the measurement is
designed to show -- IF the same level of test signal is applied to all of the
radios.
For me, primarily a contester, secondarily a DXer, the primary factors in
choosing a radio are performance in a strong signal environment, a clean TX
signal, and a very efficient user interface. After hearing Adam speak, I had
hoped that his work would contribute to that process, but because the level of
his excitation varies depending on the shortcomings of the radio, it fails to
provide useful information.
To clarify -- the strong signal performance and dynamic range of SDRs is
limited by the total voltage at the input to the digital system. If there is
no input filtering (i.e., a preselector, bandpass filter, or hardware
attenuator), the digital system sees the broadband spectrum from whatever
antenna drives it. That's everything from DC to daylight -- AM broadcast, all
the other ham bands, shortwave broadcast, all other users of the spectrum. It
is the SUM of all of those signals that combine to overload the digital
system. When that combined signal level hits digital clip (all bits are
digital zero), the radio stops working.
It is, of course, possible for the user to add bandpass filters outboard to
the radio, and many contesters with SO2R and multi-transmitter stations do so.
This would, indeed, significantly reduce the input to the digital system to
inband signals. BUT -- SO2R and multi-transmitter stations with closely spaced
antennas could still overload the digital system even with that filtering.
And there's still in-band QRM to get you to digital clip -- a ham a block or
two away running power amp, or a mile away with his antenna pointed at you,
and the sum of all the in-band signals during a major contest. In EU and AS,
there are big broadcast signals in parts of the 40M band that are going to
sail right through the world's best preselector or bandpass filter without
attenuation.
My neighbor W6DRX (0.3 miles from me and an active contester) and I both
bought K3s as soon as the radio was announced because we realized that it was
the only way we could coexist and remain friends. :)
73, Jim K9YC
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