[Elecraft] K3 to IC-7800 Comparison?

[Jim Brown]

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