here is something I found on the net that will help others to understand better
the performance data tables:
Here a few measurements of receivers, using 500Hz filters.
MDS is a measure of sensitivity. -135dBm is 10dB more sensitive than -125dBm.
This number doesn't matter very much in what you actually hear. The real test
is if you hear a very noticeable noise increase when you connect an antenna to
the receiver. If you hear an obvious noise increase when you connect an
antenna instead of a dummy load, your receiver is sensitive enough! You should
check sensitivity at the quietest time with the narrowest selectivity you use
on every antenna you use.
Contrary to folklore and hyperbole, there isn't a receiver sold today that can
dig into noise more than others on CW based on sensitivity or the use of a DSP
or multiple DSP systems. The exceptions are:
Increased selectivity will reduce noise
Poor AGC design or detector problems can cause mixing of signals and noise
If you read a review that claims a receiver made weak signals appear from
nowhere, you better keep a wary eye on the rest of the review. It is possible
for a receiver to be abnormally bad, but it is not possible for a receiver to
work better than other properly working receivers based on sensitivity.
BDR is blocking dynamic range. This is the point where a strong signal either 2
or 10kHz just starts to make your receiver lose sensitivity. The bigger the
number the better, ESPECIALLY at 2kHz spacing. The number you want here is
probably around 80dB or more if you live in a reasonably quiet location and
work weak signals on crowded bands. If you run two transmitters on the same
band or have a neighbor who operates near your frequency, you almost certainly
need more dynamic range. I'm in a very quiet rural location and have very
directive antennas, and 80dB blocking DR suits my requirements just fine most
of the time.
IMDR is intermodulation dynamic range. This is the single most important number
when comparing receivers. This is where two or more strong close-frequency
signals mix and generate a new phantom signal or multiple tones in a adjacent
frequency SSB signal mix with themselves and make what sounds like splatter.
The measurement is made just at the point where the phantom signal level is
high enough to interfere with the weakest signal your receiver can detect. IMDR
is a measure of how badly your own receiver causes problems you might blame on
other people. Bigger numbers mean better receivers. It is most important the
2kHz number be good. The 10kHz test number doesn't mean nearly as much, because
almost any radio is good enough at 10kHz or wider. Some number above 80dB is
enough to stay out of trouble 99% of the time. If you are in a noisy location,
you obviously need less performance. 85dB keeps my receivers at the point where
poor quality external signals
cause nearly all off-frequency problems. With 85dB IM3DR only a few of the
strongest stations cause my receiver to make its own internal problems.
"If freedom means something,it is the right to tell others what they don't want
to hear" –George Orwell
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