Topband: IC-756pro2 A/B Test Results

[Tom Rauch]

Assuming all of the receivers are limited by external noise and don't have
some major flaw, a weak steady carrier in broadband somewhat smooth noise
would have a S/N ratio established by selectivity. Noise drops 3dB every
time selectivity is halved, while the signal remains the same. Using a 50Hz
filter of any type, it is a given that radio would rank better than a radio
with a wide filter.

This is one of the reasons people claim PSK can "hear" signals much better
than it really can when compared to CW. People listen for CW using a wide
filter (usually over 2kHz) directly to the ear while the PSK is detected on
a narrow filter in the computer. The end results on the air can be quite
different. When the operator uses a narrow CW filter and strong signals or
erratic noise pumps the AGC system in the receiver, the results are actually
the opposite.

> >The IC-756pro2 IMDDR3 and BDR test results from the ARRL lab are not as
> >good as some of the other receivers on the list, but my tests are done
> >when there are no nearby strong signals on the band.  The sole purpose of
> >my tests is to determine how well a receiver can dig weak CW signals from
> >the noise.
> >
> When there are nearby strong signals on the band they can be part of the
> noise. If you were making your comparison with some strong nearby
> signals in the mix, you would likely rank those radios very differently.